1. What
is IOC (or Dependency Injection)?
The basic concept of the Inversion of Control pattern (also known as dependency injection) is that you do not create your objects but describe how they should be created. You don't directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (in the case of the spring framework, the IOC container) is then responsible for hooking it all up.
i.e., Applying IoC, objects are given their dependencies at creation time by some external entity that coordinates each object in the system. That is, dependencies are injected into objects. So, IoC means an inversion of responsibility with regard to how an object obtains references to collaborating objects.
The basic concept of the Inversion of Control pattern (also known as dependency injection) is that you do not create your objects but describe how they should be created. You don't directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (in the case of the spring framework, the IOC container) is then responsible for hooking it all up.
i.e., Applying IoC, objects are given their dependencies at creation time by some external entity that coordinates each object in the system. That is, dependencies are injected into objects. So, IoC means an inversion of responsibility with regard to how an object obtains references to collaborating objects.
2. What
are the different types of IOC (dependency injection) ?
There are three types of dependency injection:
There are three types of dependency injection:
- Constructor Injection (e.g. Pico container, Spring
etc): Dependencies are provided as constructor parameters.
Constructor-based
DI is realized by invoking a constructor with a number of arguments, each
representing a collaborator.
For constructor injection, we use
constructor with parameters as shown below,
public class namebean {
String name;
public namebean(String a) {
name = a;
}
}
String name;
public namebean(String a) {
name = a;
}
}
We will set the property 'name' while
creating an instance of the bean 'namebean' as namebean bean1 = new
namebean("tom");
Here we use the
<constructor-arg> element to set the the property by constructor
injection as
<bean id="bean1" class="namebean">
<constructor-arg>
<value>My Bean Value</value>
</constructor-arg>
</bean>
<bean id="bean1" class="namebean">
<constructor-arg>
<value>My Bean Value</value>
</constructor-arg>
</bean>
- Setter Injection (e.g. Spring): Dependencies are
assigned through JavaBeans properties (ex: setter methods).
Setter-based
DI is realized by calling setter methods on your beans after invoking a
no-argument constructor or no-argument static factory method to instantiate
your bean.
Normally in all the java beans, we
will use setter and getter method to set and get the value of property as
follows:
public class
namebean {
String name;
public void setName(String a) {
name = a; }
public String getName() {
return name; }
}
String name;
public void setName(String a) {
name = a; }
public String getName() {
return name; }
}
We
will create an instance of the bean 'namebean' (say bean1) and set property as
bean1.setName("tom"); Here in setter injection, we will set the
property 'name' in spring configuration file as showm below:
<bean id="bean1" class="namebean">
<property name="name" >
<value>tom</value>
</property>
</bean>
The subelement <value> sets the 'name' property by calling the set method as setName("tom"); This process is called setter injection.
To set properties that reference other beans <ref>, subelement of <property> is used as shown below,
<bean id="bean1" class="bean1impl">
<property name="game">
<ref bean="bean2"/>
</property>
</bean>
<bean id="bean2" class="bean2impl" />
- Interface Injection (e.g. Avalon): Injection is done
through an interface.
Note: Spring
supports only Constructor and Setter Injection
3. What
are the benefits of IOC (Dependency Injection)?
Benefits of IOC (Dependency Injection) are as follows:
Benefits of IOC (Dependency Injection) are as follows:
- Minimizes the amount of code in
your application. With IOC containers you do not care about how services
are created and how you get references to the ones you need. You can also
easily add additional services by adding a new constructor or a setter
method with little or no extra configuration.
- Make your application more
testable by not requiring any singletons or JNDI lookup mechanisms in your
unit test cases. IOC containers make unit testing and switching
implementations very easy by manually allowing you to inject your own
objects into the object under test.
- Loose coupling is promoted with
minimal effort and least intrusive mechanism. The factory design pattern
is more intrusive because components or services need to be requested
explicitly whereas in IOC the dependency is injected into requesting piece
of code. Also some containers promote the design to interfaces not to
implementations design concept by encouraging managed objects to implement
a well-defined service interface of your own.
- IOC containers support eager
instantiation and lazy loading of services. Containers also provide
support for instantiation of managed objects, cyclical dependencies, life
cycles management, and dependency resolution between managed objects etc.
4.
What is spring?
Spring is an open source framework created to address the complexity of enterprise application development. One of the chief advantages of the spring framework is its layered architecture, which allows you to be selective about which of its components you use while also providing a cohesive framework for J2EE application development.
Spring is an open source framework created to address the complexity of enterprise application development. One of the chief advantages of the spring framework is its layered architecture, which allows you to be selective about which of its components you use while also providing a cohesive framework for J2EE application development.
5. What
are the advantages of Spring framework?
The advantages of spring are as follows:
The advantages of spring are as follows:
- Spring has layered architecture.
Use what you need and leave you don't need now.
- Spring Enables POJO Programming.
There is no behind the scene magic here. POJO programming enables
continuous integration and testability.
- Dependency Injection and
Inversion of Control Simplifies JDBC
- Open source and no vendor
lock-in.
6. What
are features of Spring?
Lightweight:
spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 1MB. And the processing overhead is also very negligible.
spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 1MB. And the processing overhead is also very negligible.
Inversion of
control (IOC):
Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
Loose coupling is achieved in spring using the technique Inversion of Control. The objects give their dependencies instead of creating or looking for dependent objects.
Aspect oriented
(AOP):
Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
Spring supports Aspect oriented programming and enables cohesive development by separating application business logic from system services.
Container:
Spring contains and manages the life cycle and configuration of application objects.
Spring contains and manages the life cycle and configuration of application objects.
MVC Framework:
Spring comes with MVC web application framework, built on core Spring functionality. This framework is highly configurable via strategy interfaces, and accommodates multiple view technologies like JSP, Velocity, Tiles, iText, and POI. But other frameworks can be easily used instead of Spring MVC Framework.
Spring comes with MVC web application framework, built on core Spring functionality. This framework is highly configurable via strategy interfaces, and accommodates multiple view technologies like JSP, Velocity, Tiles, iText, and POI. But other frameworks can be easily used instead of Spring MVC Framework.
Transaction
Management:
Spring framework provides a generic abstraction layer for transaction management. This allowing the developer to add the pluggable transaction managers, and making it easy to demarcate transactions without dealing with low-level issues. Spring's transaction support is not tied to J2EE environments and it can be also used in container less environments.
Spring framework provides a generic abstraction layer for transaction management. This allowing the developer to add the pluggable transaction managers, and making it easy to demarcate transactions without dealing with low-level issues. Spring's transaction support is not tied to J2EE environments and it can be also used in container less environments.
JDBC Exception
Handling:
The JDBC abstraction layer of the Spring offers a meaningful exception hierarchy, which simplifies the error handling strategy. Integration with Hibernate, JDO, and iBATIS: Spring provides best Integration services with Hibernate, JDO and iBATIS
contexts for Web-based applications. As a result, the Spring framework supports integration with Jakarta Struts. The Web module also eases the tasks of handling multi-part requests and binding request parameters to domain objects.
The JDBC abstraction layer of the Spring offers a meaningful exception hierarchy, which simplifies the error handling strategy. Integration with Hibernate, JDO, and iBATIS: Spring provides best Integration services with Hibernate, JDO and iBATIS
contexts for Web-based applications. As a result, the Spring framework supports integration with Jakarta Struts. The Web module also eases the tasks of handling multi-part requests and binding request parameters to domain objects.
7. What
is web module?
This module is
built on the application context module, providing a context that is
appropriate for web-based
applications. This module also contains support for several web-oriented tasks
such as transparently handling multipart requests for file uploads and
programmatic binding of request parameters to your business objects. It also
contains integration support with Jakarta Struts.
8. What
is BeanFactory?
A BeanFactory is like a factory class that contains a collection of beans. The BeanFactory holds Bean Definitions of multiple beans within itself and then instantiates the bean whenever asked for by clients.
A BeanFactory is like a factory class that contains a collection of beans. The BeanFactory holds Bean Definitions of multiple beans within itself and then instantiates the bean whenever asked for by clients.
- BeanFactory is able to create
associations between collaborating objects as they are instantiated. This
removes the burden of configuration from bean itself and the beans client.
- BeanFactory also takes part in
the life cycle of a bean, making calls to custom initialization and
destruction methods.
9. What
is ApplicationContext?
A bean factory is fine to simple applications, but to take advantage of the full power of the Spring framework, you may want to move up to Springs more advanced container, the application context. On the surface, an application context is same as a bean factory. Both load bean definitions, wire beans together, and dispense beans upon request. But it also provides:
A bean factory is fine to simple applications, but to take advantage of the full power of the Spring framework, you may want to move up to Springs more advanced container, the application context. On the surface, an application context is same as a bean factory. Both load bean definitions, wire beans together, and dispense beans upon request. But it also provides:
- A means for resolving text
messages, including support for internationalization.
- A generic way to load file
resources, such as images.
- Events to beans that are
registered as listeners.
10. What
is the difference between BeanFactory and ApplicationContext?
On the surface, an application context is same as a bean factory. But application context offers much more...
On the surface, an application context is same as a bean factory. But application context offers much more...
- Application contexts provide a
means for resolving text messages, including support for i18n of those
messages.
- Application contexts provide a
generic way to load file resources, such as images.
- Application contexts can publish
events to beans that are registered as listeners.
- Certain operations on the
container or beans in the container, which have to be handled in a programmatic
fashion with a bean factory, can be handled declaratively in an
application context.
- ResourceLoader support: Spring’s
Resource interface us a flexible generic abstraction for handling
low-level resources. An application context itself is a ResourceLoader,
Hence provides an application with access to deployment-specific Resource
instances.
- MessageSource support: The
application context implements MessageSource, an interface used to obtain
localized messages, with the actual implementation being pluggable
11. What
are the common implementations of the ApplicationContext?
The three commonly used implementation of 'ApplicationContext' are
The three commonly used implementation of 'ApplicationContext' are
- ClassPathXmlApplicationContext:
It Loads context definition from an XML file located in the classpath,
treating context definitions as classpath resources. The application context is
loaded from the application's classpath by using the code.
ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
- FileSystemXmlApplicationContext:
It loads context definition from
an XML file in the filesystem. The application context is loaded from the file
system by using the code.
ApplicationContext context = new FileSystemXmlApplicationContext("bean.xml");
ApplicationContext context = new FileSystemXmlApplicationContext("bean.xml");
- XmlWebApplicationContext:
It loads context
definition from an XML file contained within a web application.
12. How
is a typical spring implementation look like?
For a typical Spring Application we need the following files:
For a typical Spring Application we need the following files:
- An interface that defines the
functions.
- An Implementation that contains
properties, its setter and getter methods, functions etc.,
- Spring AOP (Aspect Oriented
Programming)
- A XML file called Spring
configuration file.
- Client program that uses the
function.
13.
What is the typical Bean life cycle in Spring BeanFactory Container?
Bean life cycle in Spring Bean Factory Container is as follows:
Bean life cycle in Spring Bean Factory Container is as follows:
- The spring container finds the
bean’s definition from the XML file and instantiates the bean.
- Using the dependency injection,
spring populates all of the properties as specified in the bean definition
- If the bean implements the
BeanNameAware interface, the factory calls setBeanName () passing the
bean’s ID.
- If the bean implements the
BeanFactoryAware interface, the factory calls setBeanFactory (), passing
an instance of itself.
- If there are any
BeanPostProcessors associated with the bean, their post-
ProcessBeforeInitialization() methods will be called.
- If an init-method is specified
for the bean, it will be called.
- Finally, if there are any
BeanPostProcessors associated with the bean, their
postProcessAfterInitialization() methods will be called.
14. What
do you mean by Bean wiring?
The act of creating associations between application components (beans) within the Spring container is referred to as Bean wiring.
The act of creating associations between application components (beans) within the Spring container is referred to as Bean wiring.
15. What
do you mean by Auto Wiring?
The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory. The autowiring functionality has five modes.
The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory. The autowiring functionality has five modes.
|
Autowiring
Mode
|
Description
|
|
no
|
No autowiring
is performed. All references to other beans must be explicitly injected. This
is the default mode.
|
|
byName
|
Based on the
name of a property, a matching bean name in the IoC container will be
injected into this property if it exists.
|
|
byType
|
Based on the
type of class on a setter, if only one instance of the class exists in the
IoC container it will be injected into this property. If there is more than
one instance of the class a fatal exception is thrown.
|
|
constructor
|
Based on a
constructor argument's class types, if only one instance of the class exists
in the IoC container it will be used in the constructor.
|
|
autodetect
|
If there is a
valid constructor, the constructor autowiring mode will be chosen. Otherwise
if there is a default zero argument constructor the byType autowiring mode
will be chosen.
|
16. Inheritance in spring ?
By inheritance we mean a way
of forming new classes using classes that have already been defined. Here we
have created a simple bean and used this bean as a template for creating other
beans.
<bean id="parent" class="mybean" >
<property name="name" value="Roseindia.net"/>
</bean>
<bean id="child" class="mybean" parent="parent">
<property name="address" value="Rohini"/>
</bean>
Parent="parent":-Specify that this bean is inheriting
the properties of some other bean.
17. How
to integrate your Struts application with Spring?
To integrate your Struts application with Spring, we have two options:
To integrate your Struts application with Spring, we have two options:
- Configure Spring to manage your
Actions as beans, using the ContextLoaderPlugin, and set their
dependencies in a Spring context file.
- Subclass Spring's ActionSupport
classes and grab your Spring-managed beans explicitly using a
getWebApplicationContext() method.
18. What
are ORM’s Spring supports?
Spring supports the following ORM’s:
Spring supports the following ORM’s:
- Hibernate
- iBatis
- JPA (Java Persistence API)
- TopLink
- JDO (Java Data Objects)
- OJB
19 .What
are the ways to access Hibernate using Spring?
There are two approaches to Spring’s Hibernate integration:
There are two approaches to Spring’s Hibernate integration:
- Inversion of Control with a
HibernateTemplate and Callback
- Extending HibernateDaoSupport and
Applying an AOP Interceptor
20. How
to integrate Spring and Hibernate using HibernateDaoSupport?
Spring and Hibernate can integrate using Spring’s SessionFactory called LocalSessionFactory. The integration process is of 3 steps.
Spring and Hibernate can integrate using Spring’s SessionFactory called LocalSessionFactory. The integration process is of 3 steps.
- Configure the Hibernate
SessionFactory
- Extend your DAO Implementation
from HibernateDaoSupport
- Wire in Transaction Support with
AOP
21. What
are Bean scopes in Spring Framework ?
The Spring Framework supports exactly five scopes (of which three are available only if you are using a web-aware ApplicationContext). The scopes supported are listed below:
The Spring Framework supports exactly five scopes (of which three are available only if you are using a web-aware ApplicationContext). The scopes supported are listed below:
|
Scope
Singleton
Prototype
Request
Session
global session
ApplicationContext.
26. What is AOP? |
Description
Scopes a single bean definition to a single object instance per
Spring IoC container.
Scopes a single bean definition to any number object instances.
Scopes a single bean definition to the lifecycle of a single
HTTP request; that i
each and every HTTP
request will have its own instance of a bean created off the
back of a single bean definition. Only valid in the context of a
web-aware Spring
ApplicationContext.
Scopes a single bean definition to the lifecycle of a HTTP Session. Only valid in
the context of a
web-aware Spring ApplicationContext.
Scopes a single bean definition to the lifecycle of a global
HTTP Session. Typically
only valid when used in a portlet context. Only
valid in the
context of a web-aware Spring
|
Aspect-oriented
programming, or AOP, is a programming technique that allows programmers to
modularize crosscutting concerns, or behavior that cuts across the typical
divisions of responsibility, such as logging and transaction management. The
core construct of AOP is the aspect, which encapsulates behaviors affecting
multiple classes into reusable modules.
27. How the
AOP used in Spring?
AOP is used in the Spring Framework: To provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management, which builds on the Spring Framework's transaction abstraction. To allow users to implement custom aspects, complementing their use of OOP with AOP.
AOP is used in the Spring Framework: To provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management, which builds on the Spring Framework's transaction abstraction. To allow users to implement custom aspects, complementing their use of OOP with AOP.
28. What do
you mean by Aspect?
A modularization of a concern that cuts across multiple objects. Transaction management is a good example of a crosscutting concern in J2EE applications. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (@AspectJ style).
A modularization of a concern that cuts across multiple objects. Transaction management is a good example of a crosscutting concern in J2EE applications. In Spring AOP, aspects are implemented using regular classes (the schema-based approach) or regular classes annotated with the @Aspect annotation (@AspectJ style).
29. What do
you mean by JointPoint?
A point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.
A point during the execution of a program, such as the execution of a method or the handling of an exception. In Spring AOP, a join point always represents a method execution.
30. What do
you mean by Advice?
Action taken by an aspect at a particular joins point. Different types of advice include "around," "before" and "after" advice. Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors "around" the join point.
Action taken by an aspect at a particular joins point. Different types of advice include "around," "before" and "after" advice. Many AOP frameworks, including Spring, model an advice as an interceptor, maintaining a chain of interceptors "around" the join point.
31. What are
the types of Advice?
Types of advice:
Types of advice:
- Before advice: Advice that executes before a
join point, but which does not have the ability to prevent execution flow
proceeding to the join point (unless it throws an exception).
- After returning advice: Advice to be executed after a
join point completes normally: for example, if a method returns without
throwing an exception.
- After throwing advice: Advice to be executed if a
method exits by throwing an exception.
- After (finally) advice: Advice to be executed
regardless of the means by which a join point exits (normal or exceptional
return).
- Around advice: Advice that surrounds a join
point such as a method invocation. This is the most powerful kind of
advice. Around advice can perform custom behavior before and after the
method invocation. It is also responsible for choosing whether to proceed
to the join point or to shortcut the advised method execution by returning
its own return value or throwing an exception
32. What are
the types of the transaction management Spring supports?
Spring Framework supports:
Spring Framework supports:
- Programmatic transaction
management.
- Declarative transaction
management.
33. What are
the benefits of the Spring Framework transaction management?
The Spring Framework provides a consistent abstraction for transaction management that delivers the following benefits:
The Spring Framework provides a consistent abstraction for transaction management that delivers the following benefits:
- Provides a consistent programming
model across different transaction APIs such as JTA, JDBC, Hibernate, JPA,
and JDO.
- Supports declarative transaction
management.
- Provides a simpler API for
programmatic transaction management than a number of complex transaction
APIs such as JTA.
- Integrates very well with Spring's
various data access abstractions.
34. Why
most users of the Spring Framework choose declarative transaction management?
Most users of the Spring Framework choose declarative transaction management because it is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container.
Most users of the Spring Framework choose declarative transaction management because it is the option with the least impact on application code, and hence is most consistent with the ideals of a non-invasive lightweight container.
35. Explain
the similarities and differences between EJB CMT and the Spring Framework's
declarative transaction management?
The basic approach is similar: it is possible to specify transaction behavior (or lack of it) down to individual method level. It is
possible to make a setRollbackOnly() call within a transaction context if necessary. The differences are:
The basic approach is similar: it is possible to specify transaction behavior (or lack of it) down to individual method level. It is
possible to make a setRollbackOnly() call within a transaction context if necessary. The differences are:
- Unlike EJB CMT, which is tied to
JTA, the Spring Framework’s declarative transaction management works in
any environment? It can work with JDBC, JDO, Hibernate or other
transactions under the covers, with configuration changes only.
- The Spring Framework enables
declarative transaction management to be applied to any class, not merely
special classes such as EJBs.
- The Spring Framework offers
declarative rollback rules: this is a feature with no EJB equivalent. Both
programmatic and declarative support for rollback rules is provided.
- The Spring Framework gives you an
opportunity to customize transactional behavior, using AOP. With EJB CMT,
you have no way to influence the container's transaction management other
than setRollbackOnly().
- The Spring Framework does not
support propagation of transaction contexts across remote calls, as do
high-end application servers.
36. What
are object/relational mapping integration module?
Spring also
supports for using of an object/relational mapping (ORM) tool over straight
JDBC by providing the ORM module. Spring provide support to tie into several
popular ORM frameworks, including Hibernate, JDO, and iBATIS
SQL Maps. Spring’s transaction management supports each of these ORM
frameworks as well as JDBC.
37. When to
use programmatic and declarative transaction management ?
Programmatic transaction management is usually a good idea only if you have a small number of transactional operations.
On the other hand, if your application has numerous transactional operations, declarative transaction management is usually worthwhile. It keeps transaction management out of business logic, and is not difficult to configure.
Programmatic transaction management is usually a good idea only if you have a small number of transactional operations.
On the other hand, if your application has numerous transactional operations, declarative transaction management is usually worthwhile. It keeps transaction management out of business logic, and is not difficult to configure.
38. Explain
about the Spring DAO support?
The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.
39. What are the exceptions thrown by the Spring DAO classes ?
Spring DAO classes throw exceptions which are subclasses of DataAccessException(org.springframework.dao.DataAccessException).Spring provides a convenient translation from technology-specific exceptions like SQLException to its own exception class hierarchy with the DataAccessException as the root exception. These exceptions wrap the original exception.
The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.
39. What are the exceptions thrown by the Spring DAO classes ?
Spring DAO classes throw exceptions which are subclasses of DataAccessException(org.springframework.dao.DataAccessException).Spring provides a convenient translation from technology-specific exceptions like SQLException to its own exception class hierarchy with the DataAccessException as the root exception. These exceptions wrap the original exception.
40. What is
SQLExceptionTranslator ?
SQLExceptionTranslator, is an interface to be implemented by classes that can translate between SQLExceptions and Spring's own data-access-strategy-agnostic org.springframework.dao.DataAccessException.
SQLExceptionTranslator, is an interface to be implemented by classes that can translate between SQLExceptions and Spring's own data-access-strategy-agnostic org.springframework.dao.DataAccessException.
41. What is
Spring's JdbcTemplate ?
Spring's JdbcTemplate is central class to interact with a database through JDBC. JdbcTemplate provides many convenience methods for doing things such as converting database data into primitives or objects, executing prepared and callable statements, and providing custom database error handling.
JdbcTemplate template = new JdbcTemplate(myDataSource);
Spring's JdbcTemplate is central class to interact with a database through JDBC. JdbcTemplate provides many convenience methods for doing things such as converting database data into primitives or objects, executing prepared and callable statements, and providing custom database error handling.
JdbcTemplate template = new JdbcTemplate(myDataSource);
42. What is
PreparedStatementCreator ?
PreparedStatementCreator:
PreparedStatementCreator:
- Is one of the most common used
interfaces for writing data to database.
- Has one method –
createPreparedStatement(Connection)
- Responsible for creating a
PreparedStatement.
- Does not need to handle
SQLExceptions.
43. What is
SQLProvider ?
SQLProvider:
SQLProvider:
- Has one method – getSql()
- Typically implemented by
PreparedStatementCreator implementers.
- Useful for debugging.
44. What is
RowCallbackHandler ?
The RowCallbackHandler interface extracts values from each row of a ResultSet.
The RowCallbackHandler interface extracts values from each row of a ResultSet.
- Has one method –
processRow(ResultSet)
- Called for each row in ResultSet.
- Typically stateful.
45. What are
the differences between EJB and Spring ?
Spring
and EJB feature comparison.
|
Feature |
EJB
|
Spring
|
|
|
Transaction
management
|
|
|
|
|
Declarative
transaction support
|
|
|
|
|
Persistence
|
Supports
programmatic bean-managed persistence and declarative container managed
persistence.
|
Provides a
framework for integrating with several persistence technologies, including
JDBC, Hibernate, JDO, and iBATIS.
|
|
|
Declarative
security
|
|
|
|
|
Distributed
computing
|
Provides
container-managed remote method calls.
|
Provides
proxying for remote calls via RMI, JAX-RPC, and web services.
|
|
46 . Do I need
any other SOAP framework to run Spring Web Services?
You don't need
any other SOAP framework to use Spring Web services, though it can use
some of the
features of Axis 1 and 2.
47 . I get
NAMESPACE_ERR exceptions when using Spring-WS. What can I do about it?
If you get the following Exception:
NAMESPACE_ERR: An attempt is made to create or change an object in a way which is incorrect with regard to namespaces.
Most often, this exception is related to an older version of Xalan being used. Make sure to upgrade to 2.7.0.
If you get the following Exception:
NAMESPACE_ERR: An attempt is made to create or change an object in a way which is incorrect with regard to namespaces.
Most often, this exception is related to an older version of Xalan being used. Make sure to upgrade to 2.7.0.
48 .Does
Spring-WS run under Java 1.3?
Spring Web Services requires Java 1.4 or higher.
Spring Web Services requires Java 1.4 or higher.
49. Does Spring-WS
work under Java 1.4?
Spring Web Services works under Java 1.4, but it requires some effort to make it work. Java 1.4 is bundled with the older XML parser Crimson, which does not handle namespaces correctly. Additionally, it is bundled with an older version of Xalan, which also has problems. Unfortunately, placing newer versions of these on the class path does not override them. .
The only solution that works is to add newer versions of Xerces and Xalan in the lib/endorsed directory of your JDK, as explained in those FAQs (i.e.$JAVA_HOME/lib/endorsed). The following libraries are known to work with Java 1.4.2:
Spring Web Services works under Java 1.4, but it requires some effort to make it work. Java 1.4 is bundled with the older XML parser Crimson, which does not handle namespaces correctly. Additionally, it is bundled with an older version of Xalan, which also has problems. Unfortunately, placing newer versions of these on the class path does not override them. .
The only solution that works is to add newer versions of Xerces and Xalan in the lib/endorsed directory of your JDK, as explained in those FAQs (i.e.$JAVA_HOME/lib/endorsed). The following libraries are known to work with Java 1.4.2:
|
Library |
Version
|
|
2.8.1
|
|
|
2.7.0
|
|
|
1.3.04
|
|
|
1.2
|
If you want to
use WS-Security, note that the XwsSecurityInterceptor requires Java 5, because
an underlying library (XWSS) requires it. Instead, you can use the
Wss4jSecurityInterceptor.
50 .Does
Spring-WS work under Java 1.6?
Java 1.6 ships with SAAJ 1.3, JAXB 2.0, and JAXP 1.4 (a custom version of Xerces and Xalan). Overriding these libraries by putting different version on the classpath will result in various classloading issues, or exceptions in org.apache.xml.serializer.ToXMLSAXHandler. The only option for using more recent versions is to put the newer version in the endorsed directory (see above).
Java 1.6 ships with SAAJ 1.3, JAXB 2.0, and JAXP 1.4 (a custom version of Xerces and Xalan). Overriding these libraries by putting different version on the classpath will result in various classloading issues, or exceptions in org.apache.xml.serializer.ToXMLSAXHandler. The only option for using more recent versions is to put the newer version in the endorsed directory (see above).
51 . Why do the
Spring-WS unit tests fail under Mac OS X?
For some reason, Apple decided to include a Java 1.4 compatibility jar with their JDK 1.5. This jar includes the XML parsers which were included in Java 1.4. No other JDK distribution does this, so it is unclear what the purpose of this compatibility jar is.
The jar can be found at /System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Classes/.compatibility/14compatibility.jar. You can safely remove or rename it, and the tests will run again.
For some reason, Apple decided to include a Java 1.4 compatibility jar with their JDK 1.5. This jar includes the XML parsers which were included in Java 1.4. No other JDK distribution does this, so it is unclear what the purpose of this compatibility jar is.
The jar can be found at /System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Classes/.compatibility/14compatibility.jar. You can safely remove or rename it, and the tests will run again.
52 . What is
SAAJ?
SAAJ is the SOAP with Attachments API for Java. Like most Java EE libraries, it consists of a set of interfaces (saaj-api.jar), and implementations (saaj-impl.jar). When running in a Application Server, the implementation is typically provided by the application server. Previously, SAAJ has been part of JAXM, but it has been released as a seperate API as part of the , and also as part of J2EE 1.4. SAAJ is generally known as the packagejavax.xml.soap.
Spring-WS uses this standard SAAJ library to create representations of SOAP messages. Alternatively, it can use
SAAJ is the SOAP with Attachments API for Java. Like most Java EE libraries, it consists of a set of interfaces (saaj-api.jar), and implementations (saaj-impl.jar). When running in a Application Server, the implementation is typically provided by the application server. Previously, SAAJ has been part of JAXM, but it has been released as a seperate API as part of the , and also as part of J2EE 1.4. SAAJ is generally known as the packagejavax.xml.soap.
Spring-WS uses this standard SAAJ library to create representations of SOAP messages. Alternatively, it can use
53 . What version
of SAAJ does my application server support?
|
Application Server |
SAAJ Version
|
|
|
BEA WebLogic 8
|
1.1
|
|
|
BEA WebLogic 9
|
1.1/1.2*
|
|
|
BEA WebLogic 10
|
1.3**
|
|
|
IBM WebSphere 6
|
1.2
|
|
|
SUN Glassfish 1
|
1.3
|
|
|
JBoss 4.2
|
1.3***
|
|
54 .I get a
NoSuchMethodError when using SAAJ. What can I do about it?
If you get the following stack trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.ws.soap.saaj.SaajSoapMessageFactory' defined in ServletContext resource [/WEB-INF/springws-servlet.xml]:
Invocation of init method failed;
nested exception is java.lang.NoSuchMethodError:
javax.xml.soap.MessageFactory.newInstance(Ljava/lang/String;)Ljavax/xml/soap/MessageFactory;
Caused by:
java.lang.NoSuchMethodError:
javax.xml.soap.MessageFactory.newInstance(Ljava/lang/String;)Ljavax/xml/soap/MessageFactory;
Like most J2EE libraries, SAAJ consists of two parts: the API that consists of interfaces (saaj-api.jar) and the implementation (saaj-impl.jar). The stack trace is due to the fact that you are using a new version of the API (SAAJ 1.3), while your application server provides an earlier version of the implementation (SAAJ 1.2 or even 1.1). Spring-WS supports all three versions of SAAJ (1.1 through 1.3), but things break when it sees the 1.3 API, while there is no 1.3 implementation.
The solution therefore is quite simple: to remove the newer 1.3 version of the API, from the class path, and replace it with the version supported by your application server.
If you get the following stack trace:
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.ws.soap.saaj.SaajSoapMessageFactory' defined in ServletContext resource [/WEB-INF/springws-servlet.xml]:
Invocation of init method failed;
nested exception is java.lang.NoSuchMethodError:
javax.xml.soap.MessageFactory.newInstance(Ljava/lang/String;)Ljavax/xml/soap/MessageFactory;
Caused by:
java.lang.NoSuchMethodError:
javax.xml.soap.MessageFactory.newInstance(Ljava/lang/String;)Ljavax/xml/soap/MessageFactory;
Like most J2EE libraries, SAAJ consists of two parts: the API that consists of interfaces (saaj-api.jar) and the implementation (saaj-impl.jar). The stack trace is due to the fact that you are using a new version of the API (SAAJ 1.3), while your application server provides an earlier version of the implementation (SAAJ 1.2 or even 1.1). Spring-WS supports all three versions of SAAJ (1.1 through 1.3), but things break when it sees the 1.3 API, while there is no 1.3 implementation.
The solution therefore is quite simple: to remove the newer 1.3 version of the API, from the class path, and replace it with the version supported by your application server.
55 . I get an
UnsupportedOperationException "This class does not support SAAJ 1.1"
when I use SAAJ under WebLogic 9. What can I do about it?
WebLogic 9 has a known bug in the SAAJ 1.2 implementation: it implement all the 1.2 interfaces, but throws UnsupportedOperationExceptions when you call them. Confusingly, the exception message is This class does not support SAAJ 1.1, even though it supports SAAJ 1.1 just fine; it just doesn't support SAAJ 1.2. See alsot
Spring-WS has a workaround for this, we basically use SAAJ 1.1 only when dealing with WebLogic 9. Unfortunately, other frameworks which depend on SAAJ, such as XWSS, do not have this workaround. These frameworks happily call SAAJ 1.2 methods, which throw this exception.
The solution is to not use BEA's version of SAAJ, but to use another implementation, like the one from Axis 1, or SUN. In you application context, use the following:
<bean id="messageFactory" class="org.springframework.ws.soap.saaj.SaajSoapMessageFactory">
<property name="messageFactory">
<bean class="com.sun.xml.messaging.saaj.soap.MessageFactoryImpl"/>
</property>
</bean>
WebLogic 9 has a known bug in the SAAJ 1.2 implementation: it implement all the 1.2 interfaces, but throws UnsupportedOperationExceptions when you call them. Confusingly, the exception message is This class does not support SAAJ 1.1, even though it supports SAAJ 1.1 just fine; it just doesn't support SAAJ 1.2. See alsot
Spring-WS has a workaround for this, we basically use SAAJ 1.1 only when dealing with WebLogic 9. Unfortunately, other frameworks which depend on SAAJ, such as XWSS, do not have this workaround. These frameworks happily call SAAJ 1.2 methods, which throw this exception.
The solution is to not use BEA's version of SAAJ, but to use another implementation, like the one from Axis 1, or SUN. In you application context, use the following:
<bean id="messageFactory" class="org.springframework.ws.soap.saaj.SaajSoapMessageFactory">
<property name="messageFactory">
<bean class="com.sun.xml.messaging.saaj.soap.MessageFactoryImpl"/>
</property>
</bean>
56 . I get an
UnsupportedOperationException "This class does not support SAAJ 1.1"
when I use SAAJ under WebLogic 10. What can I do about it?
Weblogic 10 ships with two SAAJ implementations. By default the buggy 9.x implementation is used (which lives in the package weblogic.webservice.core.soap), but there is a new implementation, which supports SAAJ 1.3 (which lives in the package weblogic.xml.saaj). By looking at the DEBUG logging when Spring Web Services starts up, you can see which SAAJ implementation is used.
To use this new version, you have to create a message factory bean like so:
<bean id="messageFactory" class="org.springframework.ws.soap.saaj.SaajSoapMessageFactory">
<property name="messageFactory">
<bean class="weblogic.xml.saaj.MessageFactoryImpl"/>
</property>
</bean>
Weblogic 10 ships with two SAAJ implementations. By default the buggy 9.x implementation is used (which lives in the package weblogic.webservice.core.soap), but there is a new implementation, which supports SAAJ 1.3 (which lives in the package weblogic.xml.saaj). By looking at the DEBUG logging when Spring Web Services starts up, you can see which SAAJ implementation is used.
To use this new version, you have to create a message factory bean like so:
<bean id="messageFactory" class="org.springframework.ws.soap.saaj.SaajSoapMessageFactory">
<property name="messageFactory">
<bean class="weblogic.xml.saaj.MessageFactoryImpl"/>
</property>
</bean>
57 . I get an
IndexOutOfBoundsException when I use SAAJ under JBoss. What can I do about it?
The SAAJ implementation provided by JBoss has some issues. The solution is therefore not to use the JBoss implementation, but to use another implementation. For instance, you can use SUN's reference implementation like so:
<bean id="messageFactory" class="org.springframework.ws.soap.saaj.SaajSoapMessageFactory">
<property name="messageFactory">
<bean class="com.sun.xml.messaging.saaj.soap.ver1_1.SOAPMessageFactory1_1Impl"/>
</property>
</bean>
The SAAJ implementation provided by JBoss has some issues. The solution is therefore not to use the JBoss implementation, but to use another implementation. For instance, you can use SUN's reference implementation like so:
<bean id="messageFactory" class="org.springframework.ws.soap.saaj.SaajSoapMessageFactory">
<property name="messageFactory">
<bean class="com.sun.xml.messaging.saaj.soap.ver1_1.SOAPMessageFactory1_1Impl"/>
</property>
</bean>
58 . Does
Spring-WS run on IBM WebSphere?
WebSphere bundles some libraries which are out-of-date, and need to be upgraded with more recent versions. Specifically, this includes XML-apis, Xerces, Xalan, and WSDL4J.
There are a couple of ways to upgrade these libraries, all using parent-last or application-first classloading.
WebSphere bundles some libraries which are out-of-date, and need to be upgraded with more recent versions. Specifically, this includes XML-apis, Xerces, Xalan, and WSDL4J.
There are a couple of ways to upgrade these libraries, all using parent-last or application-first classloading.
- Package the libraries as part of
the WAR (in WEB-INF/lib), and run the web application with the parent-last
(application-first) classloading.
- Package the libraries as part of
the EAR, add class-path entries to the manifest of the web application,
and run the entire application with the parent-last classloading.
- Create a new classloader in the
WebSphere console, and associate the libraries with. Set this classloader
to parent-last.
The last approach
has the advantage of restricting the parent-last classloading to the
conflicting libraries only, and not to the entire application.
59. Why
does Spring-WS only support contract-first?
Note that Spring-WS only requires you to write the XSD; the WSDL can be generated from that.
Note that Spring-WS only requires you to write the XSD; the WSDL can be generated from that.
60 . How do I
retrieve the WSDL from a Service?
The &WSDL query parameter does not work.
The &WSDL query parameter is a way to get a WSDL of a class. In SWS, a service is generally not implemented as a single class, but as a collection of endpoints.
There are two ways to expose a WSDL:
The &WSDL query parameter does not work.
The &WSDL query parameter is a way to get a WSDL of a class. In SWS, a service is generally not implemented as a single class, but as a collection of endpoints.
There are two ways to expose a WSDL:
- Simply add the WSDL to the root
of the WAR, and the file is served normally. This has the disadvantage
that the "location" attribute in the WSDL is static, i.e. it
does not necessarily reflect the host name of the server. You can
transform locations by using a WsdlDefinitionHandlerAdapter.
- Use theMessageDispatcherServlet,
which is done is the samples. Every WsdlDefinition listed in the
*-servlet.xml will be exposed under the bean name. So if you define a WsdlDefinition
namedecho, it will be exposed as echo.wsdl
(i.e.http://localhost:8080/echo/echo.wsdl).
61 What is web
module?
Spring comes with
a full-featured MVC framework for building web applications. Although Spring
can easily be integrated with other MVC frameworks, such as Struts, Spring’s
MVC framework uses IoC to provide for a clean separation of controller logic
from business objects. It also allows you to declaratively bind request
parameters to your business objects. It also can take advantage of any of
Spring’s other services, such as I18N messaging and validation.
62 What is a
BeanFactory?
A BeanFactory is
an implementation of the factory pattern that applies Inversion of Control to
separate the application’s configuration and dependencies from the actual
application code.
63 What is AOP
Alliance?
AOP Alliance is
an open-source project whose goal is to promote adoption of AOP and
interoperability among different AOP implementations by defining a common set
of interfaces and components.
64 What is Spring
configuration file?
Spring
configuration file is an XML file. This file contains the classes information
and describes how these classes are configured and introduced to each other.
65 .What does a
simple spring application contain?
These applications
are like any Java application. They are made up of several classes, each
performing a specific purpose within the application. But these classes are
configured and introduced to each other through an XML file. This XML file
describes how to configure the classes, known as theSpring configuration file.
66 What is
XMLBeanFactory?
BeanFactory has many implementations in Spring. But one of the most useful one is org.springframework.beans.factory.xml.XmlBeanFactory, which loads its beans based on the definitions contained in an XML file. To create an XmlBeanFactory, pass a java.io.InputStream to the constructor. The InputStream will provide the XML to the factory. For example, the following code snippet uses a java.io.FileInputStream to provide a bean definition XML file to XmlBeanFactory.
BeanFactory has many implementations in Spring. But one of the most useful one is org.springframework.beans.factory.xml.XmlBeanFactory, which loads its beans based on the definitions contained in an XML file. To create an XmlBeanFactory, pass a java.io.InputStream to the constructor. The InputStream will provide the XML to the factory. For example, the following code snippet uses a java.io.FileInputStream to provide a bean definition XML file to XmlBeanFactory.
BeanFactory factory = new XmlBeanFactory(new FileInputStream("beans.xml"));
To retrieve the bean from a BeanFactory, call the getBean() method by passing the name of the bean you want to retrieve.
To retrieve the bean from a BeanFactory, call the getBean() method by passing the name of the bean you want to retrieve.
MyBean myBean = (MyBean) factory.getBean("myBean")
67. What is spring? What are the various parts of spring framework? What are the different persistence frameworks which could be used with spring?
A. Spring is an open source framework created to address the complexity of enterprise application development. One of the chief advantages of the Spring framework is its layered architecture, which allows you to be selective about which of its components you use while also providing a cohesive framework for J2EE application development. The Spring modules are built on top of the core container, which defines how beans are created, configured, and managed, as shown in the following figure. Each of the modules (or components) that comprise the Spring framework can stand on its own or be implemented jointly with one or more of the others. The functionality of each component is as follows:
The core container: The core container provides the essential functionality of the Spring framework. A primary component of the core container is the BeanFactory, an implementation of the Factory pattern. The BeanFactory applies the Inversion of Control (IOC) pattern to separate an application’s configuration and dependency specification from the actual application code.
Spring context: The Spring context is a configuration file that provides context information to the Spring framework. The Spring context includes enterprise services such as JNDI, EJB, e-mail, internalization, validation, and scheduling functionality.
Spring AOP: The Spring AOP module integrates aspect-oriented programming functionality directly into the spring framework, through its configuration management feature. As a result you can easily AOP-enable any object managed by the Spring framework. The Spring AOP module provides transaction management services for objects in any Spring-based application. With Spring AOP you can incorporate declarative transaction management into your applications without relying on EJB components.
Spring DAO: The Spring JDBC DAO abstraction layer offers a meaningful exception hierarchy for managing the exception handling and error messages thrown by different database vendors. The exception hierarchy simplifies error handling and greatly reduces the amount of exception code you need to write, such as opening and closing connections. Spring DAO’s JDBC-oriented exceptions comply to its generic DAO exception hierarchy.
Spring ORM: The Spring framework plugs into several ORM frameworks to provide its Object Relational tool, including JDO, Hibernate, and iBatis SQL Maps. All of these comply to Spring’s generic transaction and DAO exception hierarchies.
Spring Web module: The Web context module builds on top of the application context module, providing contexts for Web-based applications. As a result, the Spring framework supports integration with Jakarta Struts. The Web module also eases the tasks of handling multi-part requests and binding request parameters to domain objects.
Spring MVC framework: The Model-View-Controller (MVC) framework is a full-featured MVC implementation for building Web applications. The MVC framework is highly configurable via strategy interfaces and accommodates numerous view technologies including JSP, Velocity, Tiles, iText, and POI.
68. What
is AOP? How does it relate with IOC? What are different tools to utilize AOP?
Aspect-oriented
programming, or AOP, is a programming technique that allows programmers to
modularize crosscutting concerns, or behavior that cuts across the typical
divisions of responsibility, such as logging and transaction management. The
core construct of AOP is the aspect, which encapsulates behaviors affecting
multiple classes into reusable modules. AOP and IOC are complementary
technologies in that both apply a modular approach to complex problems in
enterprise application development. In a typical object-oriented development
approach you might implement logging functionality by putting logger statements
in all your methods and Java classes. In an AOP approach you would instead
modularize the logging services and apply them declaratively to the components
that required logging. The advantage, of course, is that the Java class doesn't
need to know about the existence of the logging service or concern itself with
any related code. As a result, application code written using Spring AOP is
loosely coupled. The best tool to utilize AOP to its capability is AspectJ.
However AspectJ works at he byte code level and you need to use AspectJ
compiler to get the aop features built into your compiled code. Nevertheless
AOP functionality is fully integrated into the Spring context for transaction
management, logging, and various other features. In general any AOP
framework control aspects in three possible ways:
Joinpoints: Points in a program's execution. For
example, joinpoints could define calls to specific methods in a class
Pointcuts: Program constructs to designate joinpoints and collect specific context at those points
Advices: Code that runs upon meeting certain conditions. For example, an advice could log a message before executing a joinpoint
Pointcuts: Program constructs to designate joinpoints and collect specific context at those points
Advices: Code that runs upon meeting certain conditions. For example, an advice could log a message before executing a joinpoint
69 What
are the advantages of spring framework?
1. Spring has layed architecture. Use
what you need and leave you don't need now.
2. Spring Enables POJO Programming. There
is no behind the scene magic here. POJO programming enables continous
integration and testability.
3. Dependency Injection and Inversion of
Control Simplifies JDBC (Read the first question.)
4. Open source and no vendor lock-in.
70. How do add a bean in spring application?
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
<bean id="foo" class="com.act.Foo"/>
<bean id="bar" class="com.act.Bar"/>
</beans>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
<bean id="foo" class="com.act.Foo"/>
<bean id="bar" class="com.act.Bar"/>
</beans>
71. What
are singleton beans and how can you create prototype beans?
Beans defined in
spring framework are singleton beans. There is an attribute in bean tag named
‘singleton’ if specified true then bean becomes singleton and if set to false
then the bean becomes a prototype bean. By default it is set to true. So, all
the beans in spring framework are by default singleton beans.
<beans>
<bean id="bar" class="com.act.Foo" singleton=”false”/>
</beans>
<bean id="bar" class="com.act.Foo" singleton=”false”/>
</beans>
72 . What
are the important beans lifecycle methods?
There are two
important bean lifecycle methods. The first one is setup which is called when
the bean is loaded in to the container. The second method is the teardown
method which is called when the bean is unloaded from the container.
73 . How can you
override beans default lifecycle methods?
The bean tag has
two more important attributes with which you can define your own custom
initialization and destroy methods. Here I have shown a small demonstration.
Two new methods fooSetup and fooTeardown are to be added to your Foo class.
<beans>
<bean id="bar" class="com.act.Foo" init-method=”fooSetup” destroy=”fooTeardown”/>
</beans>
<bean id="bar" class="com.act.Foo" init-method=”fooSetup” destroy=”fooTeardown”/>
</beans>
74. What
are Inner Beans?
When wiring
beans, if a bean element is embedded to a property tag directly, then that bean
is said to the Inner Bean. The drawback of this bean is that it cannot be
reused anywhere else.
75. What are the
different types of bean injections?
There are two
types of bean injections.
- By setter
- By constructor
76. What is Auto
wiring?
You can wire the
beans as you wish. But spring framework also does this work for you. It can
auto wire the related beans together. All you have to do is just set the
autowire attribute of bean tag to an autowire type.
<beans>
<bean id="bar" class="com.act.Foo" Autowire=”autowire type”/>
</beans>
<bean id="bar" class="com.act.Foo" Autowire=”autowire type”/>
</beans>
77 . What are
different types of Autowire types?
There are four
different types by which autowiring can be done.
- byName
- byType
- constructor
- autodetect
78. What are the
different types of events related to Listeners?
There are a lot
of events related to ApplicationContext of spring framework. All the events are
subclasses of org.springframework.context.Application-Event. They are
- ContextClosedEvent – This is
fired when the context is closed.
- ContextRefreshedEvent – This is
fired when the context is initialized or refreshed.
- RequestHandledEvent – This is
fired when the web context handles any request.
79. What is an
Aspect?
An aspect is the
cross-cutting functionality that you are implementing. It is the aspect of your
application you are modularizing. An example of an aspect is logging. Logging
is something that is required throughout an application. However, because
applications tend to be broken down into layers based on functionality, reusing
a logging module through inheritance does not make sense. However, you can create
a logging aspect and apply it throughout your application using AOP.
80 . What is a
Jointpoint?
A joinpoint is a
point in the execution of the application where an aspect can be plugged in.
This point could be a method being called, an exception being thrown, or even a
field being modified. These are the points where your aspect’s code can be
inserted into the normal flow of your application to add new behavior.
81 What is an
Advice?
Advice is the
implementation of an aspect. It is something like telling your application of a
new behavior. Generally, and advice is inserted into an application at
joinpoints.
82 What is
a Pointcut?
A pointcut is
something that defines at what joinpoints an advice should be applied. Advices
can be applied at any joinpoint that is supported by the AOP framework. These
Pointcuts allow you to specify where theadvice can be applied.
83 What is
an Introduction in AOP?
An introduction
allows the user to add new methods or attributes to an existing class. This can
then be introduced to an existing class without having to change the structure
of the class, but give them the new behavior and state.
84 What is
a Target?
A target is the
class that is being advised. The class can be a third party class or your own
class to which you want to add your own custom behavior. By using the concepts
of AOP, the target class is free to center on its major concern, unaware to any
advice that is being applied.
85 . What is a
Proxy?
A proxy is an
object that is created after applying advice to a target object. When you think
of client objects the target object and the proxy object are the same.
86 .What is meant
by Weaving?
The process of
applying aspects to a target object to create a new proxy object is called as
Weaving. The aspects are woven intothe target object at the specified
joinpoints.
87 What are
the different points where weaving can be applied?
- Compile Time
- Classload Time
- Runtime
88. What are the
different advice types in spring?
- Around : Intercepts the calls to
the target method
- Before : This is called before
the target method is invoked
- After : This is called after the
target method is returned
- Throws : This is called when the
target method throws and exception
- Around :
org.aopalliance.intercept.MethodInterceptor
- Before : org.springframework.aop.BeforeAdvice
- After :
org.springframework.aop.AfterReturningAdvice
- Throws :
org.springframework.aop.ThrowsAdvice
89. What are the different types of AutoProxying?
- BeanNameAutoProxyCreator
- DefaultAdvisorAutoProxyCreator
- Metadata autoproxying
·
90 What kind of exceptions those spring DAO classes throw?
·
The spring’s DAO class does not throw any technology
related exceptions such as SQLException. They throw exceptions which are
subclasses of DataAccessException.
·
91 What is DataAccessException?
·
DataAccessException is a RuntimeException. This is an
Unchecked Exception. The user is not forced to handle these kinds of
exceptions.
·
92 How can you configure a bean to get DataSource from
JNDI?
·
<bean id="dataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
<property name="jndiName">
<value>java:comp/env/jdbc/myDatasource</value>
</property>
</bean>
<property name="jndiName">
<value>java:comp/env/jdbc/myDatasource</value>
</property>
</bean>
90. How can you create a DataSource connection pool?
·
<bean id="dataSource"
class="org.apache.commons.dbcp.BasicDataSource">
<property name="driver">
<value>${db.driver}</value>
</property>
<property name="url">
<value>${db.url}</value>
</property>
<property name="username">
<value>${db.username}</value>
</property>
<property name="password">
<value>${db.password}</value>
</property>
</bean>
<property name="driver">
<value>${db.driver}</value>
</property>
<property name="url">
<value>${db.url}</value>
</property>
<property name="username">
<value>${db.username}</value>
</property>
<property name="password">
<value>${db.password}</value>
</property>
</bean>
91. How JDBC can be used more efficiently in spring
framework?
·
JDBC can be used more efficiently with the help of a template
class provided by spring framework called as JdbcTemplate.
92. How JdbcTemplate
can be used?
·
With use of Spring JDBC framework the burden of resource management
and error handling is reduced a lot. So it leaves developers to write the
statements and queries to get the data to and from the database.
·
JdbcTemplate
template = new JdbcTemplate(myDataSource);
A simple DAO class looks like this.
A simple DAO class looks like this.
·
public class
StudentDaoJdbc implements StudentDao {
private JdbcTemplate jdbcTemplate;
private JdbcTemplate jdbcTemplate;
·
public void
setJdbcTemplate(JdbcTemplate jdbcTemplate) {
this.jdbcTemplate = jdbcTemplate;
}
more..
}
The configuration is shown below.
this.jdbcTemplate = jdbcTemplate;
}
more..
}
The configuration is shown below.
·
<bean
id="jdbcTemplate"
class="org.springframework.jdbc.core.JdbcTemplate">
<property name="dataSource">
<ref bean="dataSource"/>
</property>
</bean>
<bean id="studentDao" class="StudentDaoJdbc">
<property name="jdbcTemplate">
<ref bean="jdbcTemplate"/>
</property>
</bean>
<bean id="courseDao" class="CourseDaoJdbc">
<property name="jdbcTemplate">
<ref bean="jdbcTemplate"/>
</property>
</bean>
<property name="dataSource">
<ref bean="dataSource"/>
</property>
</bean>
<bean id="studentDao" class="StudentDaoJdbc">
<property name="jdbcTemplate">
<ref bean="jdbcTemplate"/>
</property>
</bean>
<bean id="courseDao" class="CourseDaoJdbc">
<property name="jdbcTemplate">
<ref bean="jdbcTemplate"/>
</property>
</bean>
93. How do you write data to backend in spring using
JdbcTemplate?
·
The JdbcTemplate uses several of these callbacks when writing
data to the database. The usefulness you will find in each of these interfaces
will vary. There are two simple interfaces. One is PreparedStatementCreator and
the other interface is BatchPreparedStatementSetter.
94. Explain about PreparedStatementCreator?
·
PreparedStatementCreator is one of the most common used interfaces
for writing data to database. The interface has one method
createPreparedStatement().
·
PreparedStatement
createPreparedStatement(Connection conn)
throws SQLException;
When this interface is implemented, we should create and return a PreparedStatement from the Connection argument, and the exception handling is automatically taken care off. When this interface is implemented, another interface SqlProvider is also implemented which has a method called getSql() which is used to provide sql strings to JdbcTemplate.
throws SQLException;
When this interface is implemented, we should create and return a PreparedStatement from the Connection argument, and the exception handling is automatically taken care off. When this interface is implemented, another interface SqlProvider is also implemented which has a method called getSql() which is used to provide sql strings to JdbcTemplate.
95. Explain about
BatchPreparedStatementSetter?
·
If the user what to update more than one row at a shot then
he can go for BatchPreparedStatementSetter. This interface provides two methods
·
setValues(PreparedStatement ps, int i) throws SQLException;
int getBatchSize();
The getBatchSize() tells the JdbcTemplate class how many statements to create. And this also determines how many times setValues() will be called.
int getBatchSize();
The getBatchSize() tells the JdbcTemplate class how many statements to create. And this also determines how many times setValues() will be called.
96. Explain about RowCallbackHandler and why it is used?
·
In order to navigate through the records we generally go for
ResultSet. But spring provides an interface that handles this entire burden and
leaves the user to decide what to do with each row. The interface provided by
spring is RowCallbackHandler. There is a method processRow() which needs to be
implemented so that it is applicable for each and everyrow.
·
void
processRow(java.sql.ResultSet rs);
·
97. What is JDBC
abstraction and DAO module?
·
Using this module we can keep up the database code clean and
simple, and prevent problems that result from a failure to close database
resources. A new layer of meaningful exceptions on top of the error messages
given by several database servers is bought in this module. In addition, this
module uses Spring’s AOP module to provide transaction management services for
objects in a Spring application.
98. How
does Spring supports DAO in hibernate?
A. Spring’s HibernateDaoSupport class is a convenient super class for Hibernate DAOs. It has handy methods you can call to get a Hibernate Session, or a SessionFactory. The most convenient method is getHibernateTemplate(), which returns a HibernateTemplate. This template wraps Hibernate checked exceptions with runtime exceptions, allowing your DAO interfaces to be Hibernate exception-free.
Example:
A. Spring’s HibernateDaoSupport class is a convenient super class for Hibernate DAOs. It has handy methods you can call to get a Hibernate Session, or a SessionFactory. The most convenient method is getHibernateTemplate(), which returns a HibernateTemplate. This template wraps Hibernate checked exceptions with runtime exceptions, allowing your DAO interfaces to be Hibernate exception-free.
Example:
public class
UserDAOHibernate extends HibernateDaoSupport {
public User
getUser(Long id) {
return (User) getHibernateTemplate().get(User.class, id);
}
public void saveUser(User user) {
getHibernateTemplate().saveOrUpdate(user);
if (log.isDebugEnabled()) {
log.debug(“userId set to: “ + user.getID());
}
}
public void removeUser(Long id) {
Object user = getHibernateTemplate().load(User.class, id);
getHibernateTemplate().delete(user);
}
return (User) getHibernateTemplate().get(User.class, id);
}
public void saveUser(User user) {
getHibernateTemplate().saveOrUpdate(user);
if (log.isDebugEnabled()) {
log.debug(“userId set to: “ + user.getID());
}
}
public void removeUser(Long id) {
Object user = getHibernateTemplate().load(User.class, id);
getHibernateTemplate().delete(user);
}
}
99. What are the id generator classes in hibernate?
A: increment: It generates identifiers of type long, short or int that are unique only when no other process is inserting data into the same table. It should not the used in the clustered environment.
identity: It supports identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL. The returned identifier is of type long, short or int.
sequence: The sequence generator uses a sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi or a generator in Interbase. The returned identifier is of type long, short or int
hilo: The hilo generator uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a table and column (by default hibernate_unique_key and next_hi respectively) as a source of hi values. The hi/lo algorithm generates identifiers that are unique only for a particular database. Do not use this generator with connections enlisted with JTA or with a user-supplied connection.
seqhilo: The seqhilo generator uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a named database sequence.
uuid: The uuid generator uses a 128-bit UUID algorithm to generate identifiers of type string, unique within a network (the IP address is used). The UUID is encoded as a string of hexadecimal digits of length 32.
guid: It uses a database-generated GUID string on MS SQL Server and MySQL.
native: It picks identity, sequence or hilo depending upon the capabilities of the underlying database.
assigned: lets the application to assign an identifier to the object before save() is called. This is the default strategy if no <generator> element is specified.
select: retrieves a primary key assigned by a database trigger by selecting the row by some unique key and retrieving the primary key value.
foreign: uses the identifier of another associated object. Usually used in conjunction with a <one-to-one> primary key association.
100. How do you define hibernate mapping file in
spring?
A. Add the hibernate mapping file entry in mapping resource inside Spring’s applicationContext.xml file in the web/WEB-INF directory.
A. Add the hibernate mapping file entry in mapping resource inside Spring’s applicationContext.xml file in the web/WEB-INF directory.
<property
name="mappingResources">
<list>
<value>org/appfuse/model/User.hbm.xml</value>
</list>
</property>
<list>
<value>org/appfuse/model/User.hbm.xml</value>
</list>
</property>
101. How do you configure spring in a web
application?
A. It is very easy to configure any J2EE-based web application to use Spring. At the very least, you can simply add Spring’s ContextLoaderListener to your web.xml file:
A. It is very easy to configure any J2EE-based web application to use Spring. At the very least, you can simply add Spring’s ContextLoaderListener to your web.xml file:
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
102. Can you have xyz.xml file instead of
applicationcontext.xml?
A. ContextLoaderListener is a ServletContextListener that initializes when your webapp starts up. By default, it looks for Spring’s configuration file at WEB-INF/applicationContext.xml. You can change this default value by specifying a <context-param> element named “contextConfigLocation.” Example:
A. ContextLoaderListener is a ServletContextListener that initializes when your webapp starts up. By default, it looks for Spring’s configuration file at WEB-INF/applicationContext.xml. You can change this default value by specifying a <context-param> element named “contextConfigLocation.” Example:
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener
<listener-class>org.springframework.web.context.ContextLoaderListener
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/xyz.xml</param-value>
</context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/xyz.xml</param-value>
</context-param>
</listener-class>
</listener>
</listener>
103. How do you configure your database driver in
spring?
A. Using datasource "org.springframework.jdbc.datasource.DriverManagerDataSource". Example:
A. Using datasource "org.springframework.jdbc.datasource.DriverManagerDataSource". Example:
<bean
id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName">
<value>org.hsqldb.jdbcDriver</value>
</property>
<property name="url">
<value>jdbc:hsqldb:db/appfuse</value>
</property>
<property name="username"><value>sa</value></property>
<property name="password"><value></value></property>
</bean>
<property name="driverClassName">
<value>org.hsqldb.jdbcDriver</value>
</property>
<property name="url">
<value>jdbc:hsqldb:db/appfuse</value>
</property>
<property name="username"><value>sa</value></property>
<property name="password"><value></value></property>
</bean>
104. How can you configure JNDI instead of datasource in spring applicationcontext.xml?
A. Using "org.springframework.jndi.JndiObjectFactoryBean". Example:
<bean
id="dataSource"
class="org.springframework.jndi.JndiObjectFactoryBean">
<property name="jndiName">
<value>java:comp/env/jdbc/appfuse</value>
</property>
</bean>
<property name="jndiName">
<value>java:comp/env/jdbc/appfuse</value>
</property>
</bean>
Q.
What are the key benifits of Hibernate?
A: These are the key benifits of Hibernate:
A: These are the key benifits of Hibernate:
·
Transparent
persistence based on POJOs without byte code processing
·
Powerful
object-oriented hibernate query language
·
Descriptive
O/R Mapping through mapping file.
·
Automatic
primary key generation
·
Hibernate
cache : Session Level, Query and Second level cache.
·
Performance:
Lazy initialization, Outer join fetching, Batch fetching
105. What is hibernate session and session factory?
How do you configure sessionfactory in spring configuration file?
A. Hibernate Session is the main runtime interface between a Java application and Hibernate. SessionFactory allows applications to create hibernate session by reading hibernate configurations file hibernate.cfg.xml.
A. Hibernate Session is the main runtime interface between a Java application and Hibernate. SessionFactory allows applications to create hibernate session by reading hibernate configurations file hibernate.cfg.xml.
// Initialize the
Hibernate environment
Configuration cfg = new Configuration().configure();
// Create the session factory
SessionFactory factory = cfg.buildSessionFactory();
// Obtain the new session object
Session session = factory.openSession();
Configuration cfg = new Configuration().configure();
// Create the session factory
SessionFactory factory = cfg.buildSessionFactory();
// Obtain the new session object
Session session = factory.openSession();
The
call to Configuration().configure() loads the hibernate.cfg.xml configuration
file and initializes the Hibernate environment. Once the configuration is
initialized, you can make any additional modifications you desire
programmatically. However, you must make these modifications prior to creating
the SessionFactory instance. An instance of SessionFactory is typically created
once and used to create all sessions related to a given context.
The main function of the Session is to offer create, read and delete operations for instances of mapped entity classes. Instances may exist in one of three states:
The main function of the Session is to offer create, read and delete operations for instances of mapped entity classes. Instances may exist in one of three states:
transient: never persistent, not associated
with any Session
persistent: associated with a unique Session
detached: previously persistent, not associated with any Session
persistent: associated with a unique Session
detached: previously persistent, not associated with any Session
A
Hibernate Session object represents a single unit-of-work for a given data
store and is opened by a SessionFactory instance. You must close Sessions when
all work for a transaction is completed. The following illustrates a typical
Hibernate session:
Session session = null;
UserInfo user = null;
Transaction tx = null;
try {
session = factory.openSession();
tx = session.beginTransaction();
user = (UserInfo)session.load(UserInfo.class, id);
tx.commit();
} catch(Exception e) {
if (tx != null) {
try {
tx.rollback();
} catch (HibernateException e1) {
throw new DAOException(e1.toString()); }
} throw new DAOException(e.toString());
} finally {
if (session != null) {
try {
session.close();
} catch (HibernateException e) { }
}
}
106. What the difference is between hibernate get and load methods?
A. The load() method is older; get() was added to Hibernates API due to user request. The difference is trivial:
The following Hibernate code snippet retrieves a User object from the database: User user = (User) session.get(User.class, userID);
The get() method is special because the identifier uniquely identifies a single instance of a class. Hence it’s common for applications to use the identifier as a convenient handle to a persistent object. Retrieval by identifier can use the cache when retrieving an object, avoiding a database hit if the object is already cached.
Hibernate also provides a load() method: User user = (User) session.load(User.class, userID);
If load() can’t find the object in the cache or database, an exception is thrown. The load() method never returns null. The get() method returns
null if the object can’t be found. The load() method may return a proxy instead of a real persistent instance. A proxy is a placeholder instance of a runtime-generated subclass (through cglib or Javassist) of a mapped persistent class, it can initialize itself if any method is called that is not the mapped database identifier getter-method. On the other hand, get() never returns a proxy. Choosing between get() and load() is easy: If you’re certain the persistent object exists, and nonexistence would be considered exceptional, load() is a good option. If you aren’t certain there is a persistent instance with the given
identifier, use get() and test the return value to see if it’s null. Using load() has a further implication: The application may retrieve a valid reference (a proxy) to a
persistent instance without hitting the database to retrieve its persistent state. So load() might not throw an exception when it doesn’t find the persistent object
in the cache or database; the exception would be thrown later, when the proxy is accessed.
107. What type of transaction management is supported in hibernate?
A. Hibernate communicates with the database via a JDBC Connection; hence it must support both managed and non-managed transactions.
non-managed in web containers:
Session session = null;
UserInfo user = null;
Transaction tx = null;
try {
session = factory.openSession();
tx = session.beginTransaction();
user = (UserInfo)session.load(UserInfo.class, id);
tx.commit();
} catch(Exception e) {
if (tx != null) {
try {
tx.rollback();
} catch (HibernateException e1) {
throw new DAOException(e1.toString()); }
} throw new DAOException(e.toString());
} finally {
if (session != null) {
try {
session.close();
} catch (HibernateException e) { }
}
}
106. What the difference is between hibernate get and load methods?
A. The load() method is older; get() was added to Hibernates API due to user request. The difference is trivial:
The following Hibernate code snippet retrieves a User object from the database: User user = (User) session.get(User.class, userID);
The get() method is special because the identifier uniquely identifies a single instance of a class. Hence it’s common for applications to use the identifier as a convenient handle to a persistent object. Retrieval by identifier can use the cache when retrieving an object, avoiding a database hit if the object is already cached.
Hibernate also provides a load() method: User user = (User) session.load(User.class, userID);
If load() can’t find the object in the cache or database, an exception is thrown. The load() method never returns null. The get() method returns
null if the object can’t be found. The load() method may return a proxy instead of a real persistent instance. A proxy is a placeholder instance of a runtime-generated subclass (through cglib or Javassist) of a mapped persistent class, it can initialize itself if any method is called that is not the mapped database identifier getter-method. On the other hand, get() never returns a proxy. Choosing between get() and load() is easy: If you’re certain the persistent object exists, and nonexistence would be considered exceptional, load() is a good option. If you aren’t certain there is a persistent instance with the given
identifier, use get() and test the return value to see if it’s null. Using load() has a further implication: The application may retrieve a valid reference (a proxy) to a
persistent instance without hitting the database to retrieve its persistent state. So load() might not throw an exception when it doesn’t find the persistent object
in the cache or database; the exception would be thrown later, when the proxy is accessed.
107. What type of transaction management is supported in hibernate?
A. Hibernate communicates with the database via a JDBC Connection; hence it must support both managed and non-managed transactions.
non-managed in web containers:
<bean
id="transactionManager"
class="org.springframework.orm.hibernate.HibernateTransactionManager">
<property name="sessionFactory">
<ref local="sessionFactory"/>
</property>
</bean>
<property name="sessionFactory">
<ref local="sessionFactory"/>
</property>
</bean>
managed in application server using JTA:
<bean
id="transactionManager"
class="org.springframework.transaction.jta.JtaTransactionManager.">
<property name="sessionFactory">
<ref local="sessionFactory"/>
</property>
</bean>
<property name="sessionFactory">
<ref local="sessionFactory"/>
</property>
</bean>
108. What is lazy loading and how do you achieve that in hibernate?
A. Lazy setting decides whether to load child objects while loading the Parent Object. You need to specify parent class. Lazy = true in hibernate mapping file. By default the lazy loading of the child objects is true. This make sure that the child objects are not loaded unless they are explicitly invoked in the application by calling getChild() method on parent. In this case hibernate issues a fresh database call to load the child when getChild() is actually called on the Parent object. But in some cases you do need to load the child objects when parent is loaded. Just make the lazy=false and hibernate will load the child when parent is loaded from the database. Examples: Address child of User class can be made lazy if it is not required frequently. But you may need to load the Author object for Book parent whenever you deal with the book for online bookshop.
Hibernate does not support lazy initialization for detached objects. Access to a lazy association outside of the context of an open Hibernate session will result in an exception.
109. What is the different fetching strategy in Hibernate?
A. Hibernate3 defines the following fetching strategies:
Join
fetching - Hibernate
retrieves the associated instance or collection in the same SELECT, using an
OUTER JOIN.
Select fetching - a second SELECT is used to retrieve the associated entity or collection. Unless you explicitly disable lazy fetching by specifying lazy="false", this second select will only be executed when you actually access the association.
Subselect fetching - a second SELECT is used to retrieve the associated collections for all entities retrieved in a previous query or fetch. Unless you explicitly disable lazy fetching by specifying lazy="false", this second select will only be executed when you actually access the association. Batch fetching - an optimization strategy for select fetching - Hibernate retrieves a batch of entity instances or collections in a single SELECT, by specifying a list of primary keys or foreign keys.
For more details read short primer on fetching strategy at http://www.hibernate.org/315.html
Select fetching - a second SELECT is used to retrieve the associated entity or collection. Unless you explicitly disable lazy fetching by specifying lazy="false", this second select will only be executed when you actually access the association.
Subselect fetching - a second SELECT is used to retrieve the associated collections for all entities retrieved in a previous query or fetch. Unless you explicitly disable lazy fetching by specifying lazy="false", this second select will only be executed when you actually access the association. Batch fetching - an optimization strategy for select fetching - Hibernate retrieves a batch of entity instances or collections in a single SELECT, by specifying a list of primary keys or foreign keys.
For more details read short primer on fetching strategy at http://www.hibernate.org/315.html
110. What are different types of cache hibernate
supports ?
A. Caching is widely used for optimizing database applications. Hibernate uses two different caches for objects: first-level cache and second-level cache. First-level cache is associated with the Session object, while second-level cache is associated with the Session Factory object. By default, Hibernate uses first-level cache on a per-transaction basis. Hibernate uses this cache mainly to reduce the number of SQL queries it needs to generate within a given transaction. For example, if an object is modified several times within the same transaction, Hibernate will generate only one SQL UPDATE statement at the end of the transaction, containing all the modifications. To reduce database traffic, second-level cache keeps loaded objects at the Session Factory level between transactions. These objects are available to the whole application, not just to the user running the query. This way, each time a query returns an object that is already loaded in the cache, one or more database transactions potentially are avoided. In addition, you can use a query-level cache if you need to cache actual query results, rather than just persistent objects. The query cache should always be used in conjunction with the second-level cache. Hibernate supports the following open-source cache implementations out-of-the-box:
A. Caching is widely used for optimizing database applications. Hibernate uses two different caches for objects: first-level cache and second-level cache. First-level cache is associated with the Session object, while second-level cache is associated with the Session Factory object. By default, Hibernate uses first-level cache on a per-transaction basis. Hibernate uses this cache mainly to reduce the number of SQL queries it needs to generate within a given transaction. For example, if an object is modified several times within the same transaction, Hibernate will generate only one SQL UPDATE statement at the end of the transaction, containing all the modifications. To reduce database traffic, second-level cache keeps loaded objects at the Session Factory level between transactions. These objects are available to the whole application, not just to the user running the query. This way, each time a query returns an object that is already loaded in the cache, one or more database transactions potentially are avoided. In addition, you can use a query-level cache if you need to cache actual query results, rather than just persistent objects. The query cache should always be used in conjunction with the second-level cache. Hibernate supports the following open-source cache implementations out-of-the-box:
·
EHCache
is a fast, lightweight, and easy-to-use in-process cache. It supports read-only
and read/write caching, and memory- and disk-based caching. However, it does
not support clustering.
·
OSCache
is another open-source caching solution. It is part of a larger package, which
also provides caching functionalities for JSP pages or arbitrary objects. It is
a powerful and flexible package, which, like EHCache, supports read-only and
read/write caching, and memory- and disk-based caching. It also provides basic
support for clustering via either JavaGroups or JMS.
·
SwarmCache is a simple cluster-based caching solution
based on JavaGroups. It supports read-only or nonstrict read/write caching (the
next section explains this term). This type of cache is appropriate for
applications that typically have many more read operations than write
operations.
·
JBoss TreeCache is a powerful replicated (synchronous
or asynchronous) and transactional cache. Use this solution if you really need
a true transaction-capable caching architecture.
111. What are the different caching strategies?
A. The following four caching strategies are available:
A. The following four caching strategies are available:
·
Read-only:
This strategy is useful for data that is read frequently but never updated.
This is by far the simplest and best-performing cache strategy.
·
Read/write:
Read/write caches may be appropriate if your data needs to be updated. They
carry more overhead than read-only caches. In non-JTA environments, each
transaction should be completed when Session.close() or Session.disconnect() is
called.
·
Nonstrict
read/write: This strategy does not guarantee that two transactions won't
simultaneously modify the same data. Therefore, it may be most appropriate for
data that is read often but only occasionally modified.
·
Transactional:
This is a fully transactional cache that may be used only in a JTA environment.
112. How do you configure 2nd level cach in
hibernate?
A. To activate second-level caching, you need to define the hibernate.cache.provider_class property in the hibernate.cfg.xml file as follows: <hibernate-configuration>
<session-factory>
<property name="hibernate.cache.provider_class">org.hibernate.cache.EHCacheProvider</property>
</session-factory>
</hibernate-configuration>
By default, the second-level cache is activated and uses the EHCache provider.
To use the query cache you must first enable it by setting the property hibernate.cache.use_query_cache to true in hibernate. properties.
A. To activate second-level caching, you need to define the hibernate.cache.provider_class property in the hibernate.cfg.xml file as follows: <hibernate-configuration>
<session-factory>
<property name="hibernate.cache.provider_class">org.hibernate.cache.EHCacheProvider</property>
</session-factory>
</hibernate-configuration>
By default, the second-level cache is activated and uses the EHCache provider.
To use the query cache you must first enable it by setting the property hibernate.cache.use_query_cache to true in hibernate. properties.
113. What is the difference between sorted and
ordered collection in hibernate?
A. A sorted collection is sorted in-memory using java comparator, while order collection is ordered at the database level using order by clause.
A. A sorted collection is sorted in-memory using java comparator, while order collection is ordered at the database level using order by clause.
114. What are the types of
inheritence models and describe how they work like vertical inheritance and
horizontal?
A. There is three types of inheritance mapping in hibernate:
A. There is three types of inheritance mapping in hibernate:
Example: Let us
take the simple example of 3 java classes. Class Manager and Worker are
inherited from Employee Abstract class.
1. Table per concrete class with unions: In this case there will be 2 tables. Tables: Manager, Worker [all common attributes will be duplicated]
2. Table per class hierarchy: Single Table can be mapped to a class hierarchy. There will be only one table in database called 'Employee' that will represent all the attributes required for all 3 classes. But it needs some discriminating column to differentiate between Manager and worker;
3. Table per subclass: In this case there will be 3 tables represent Employee, Manager and Worker
1. Table per concrete class with unions: In this case there will be 2 tables. Tables: Manager, Worker [all common attributes will be duplicated]
2. Table per class hierarchy: Single Table can be mapped to a class hierarchy. There will be only one table in database called 'Employee' that will represent all the attributes required for all 3 classes. But it needs some discriminating column to differentiate between Manager and worker;
3. Table per subclass: In this case there will be 3 tables represent Employee, Manager and Worker
115. What is the
Query Cache?
The
Query Cache
The
other cache that is available is the query cache. The query cache effectively
holds on to the identifiers for an individual query. As described in the
documentation:
Note
that the query cache does not cache the state of the actual entities in the
result set; it caches only identifier values and results of value type. So the
query cache should always be used in conjunction with the second-level cache.
Once
enabled via the configuration of Hibernate, it is simply a matter of calling
setCacheable(true) on
your Query or Criteria object. 
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