SPRING Interview Questions Part 3

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21. How to integrate your Struts application with Spring?

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.

22. What are ORM’s Spring supports ?

Spring supports the following ORM’s :

· Hibernate

· iBatis

· JPA (Java Persistence API)

· TopLink

· JDO (Java Data Objects)

· OJB

23. What are the ways to access Hibernate using Spring ?

There are two approaches to Spring’s Hibernate integration:

· Inversion of Control with a HibernateTemplate and Callback

· Extending HibernateDaoSupport and Applying an AOP Interceptor

24. 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.

· Configure the Hibernate SessionFactory

· Extend your DAO Implementation from HibernateDaoSupport

· Wire in Transaction Support with AOP

25. 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:

Scope	Description
singleton	Scopes a single bean definition to a single object instance per Spring IoC container.
prototype	Scopes a single bean definition to any number of object instances.
request	Scopes a single bean definition to the lifecycle of a single HTTP request; that is each and every HTTP request will have its own instance of a bean made off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
session	Scopes a single bean definition to the lifecycle of a HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
global session	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 ApplicationContext.

26. What is 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.

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 vital 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 excellent 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.

30. What do you mean by Advice?

Action taken by an aspect at a particular join 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:

· 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:

· 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:

· 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.

35. Clarify 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: 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.

37. When to use programmatic and declarative transaction management ?

Programmatic transaction management is usually a excellent thought 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 hard to configure.

38. Clarify about the Spring DAO support ?

The Data Access Object (DAO) support in Spring is aimed at making it simple to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the persistence technologies honestly 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

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.

42. What is PreparedStatementCreator ?

PreparedStatementCreator:

· Is one of the most common used interfaces for writing data to database.

· Has one method – createPreparedStatement(Connection)

· Responsible for making a PreparedStatement.

· Does not need to handle SQLExceptions.

43. What is 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.

· 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	Must use a JTA transaction manager. Supports transactions that span remote method calls.	Supports multiple transaction environments through its PlatformTransactionManager interface, including JTA, Hibernate, JDO, and JDBC. Does not natively support distributed transactions—it must be used with a JTA transaction manager.
Declarative transaction support	Can define transactions declaratively through the deployment descriptor. Can define transaction behavior per method or per class by using the wildcard character *. Cannot declaratively define rollback behavior—this must be done programmatically.	Can define transactions declaratively through the Spring configuration file or through class metadata. Can define which methods to apply transaction behavior explicitly or by using regular expressions. Can declaratively define rollback behavior per method and per exception type.
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	Supports declarative security through users and roles. The management and implementation of users and roles is container specific. Declarative security is configured in the deployment descriptor.	No security implementation out-of-the box. Acegi, an open source security framework built on top of Spring, provides declarative security through the Spring configuration file or class metadata.
Distributed computing	Provides container-managed remote method calls.	Provides proxying for remote calls via RMI, JAX-RPC

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