Thursday, January 1, 2009

Spring Interview Questions

Q)What is Spring's MVC package?

This package provides a Model-View-Controller (MVC) implementation for web-applications. Spring's MVC framework is different from other implementations as it provides a clean separation between model code and web forms, and allows you to use all the other features of the Spring Framework.

Q)What are the benifits of Spring framework?

The features of Spring are as follows:

Spring has layered architecture. Use what you need and leave you don't need now.
Spring Enables POJO Programming. and POJO programming enables continuous integration and testability.
Dependency Injection and Inversion of Control Simplifies JDBC
Open source and no vendor lock-in.

Q)Explain about 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.

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.

Aspect oriented (AOP) - 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.

Framework - Spring provides most of the intra functionality
leaving rest of the coding to the developer.

Q)What is Inversion of Control(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.

Q)What are the features of IOC (Dependency Injection)?

Benefits of IOC (Dependency Injection) are as follows:

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.

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.

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.

Q)What are the different types of Inversion of Control(dependency injection) ?

Constructor Injection:
Constructor-based DI is realized by invoking a constructor with a number of arguments, each representing a collaborator.

Setter Injection:
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.

Q)What are Bean Factory and Application Context?

Bean Factory

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.

Application Context

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.
Events to beans that are registered as listeners.

Q) What are the common implementations of the Application Context ?

The three commonly used implementation of 'Application Context' 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");
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");
XmlWebApplicationContext : It loads context definition from an XML file contained within a web application.

Q)How many major modules are there in Spring? What are they?

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.

Q)What is the difference between Bean Factory and Application Context ?

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

Q)How is a typical spring implementation look like ?

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.

Q)What is the typical Bean life cycle in Spring Bean Factory Container ?

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.

Q)What do you mean by Bean wiring ?

The act of creating associations between application components (beans) within the Spring container is reffered to as Bean wiring.

Q)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.






Q)What is DelegatingVariableResolver?

Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard Java Server Faces managed beans mechanism which lets you use JSF and Spring together. This variable resolver is called as DelegatingVariableResolver

Q)How to integrate Java Server Faces (JSF) with Spring?

JSF and Spring do share some of the same features, most noticeably in the area of IOC services. By declaring JSF managed-beans in the faces-config.xml configuration file, you allow the FacesServlet to instantiate that bean at startup. Your JSF pages have access to these beans and all of their properties.We can integrate JSF and Spring in two ways:

DelegatingVariableResolver: Spring comes with a JSF variable resolver that lets you use JSF and Spring together.

include org.springframework.web.jsf.DelegatingVariableResolver in variable-resolver of faces-config

The DelegatingVariableResolver will first delegate value lookups to the default resolver of the underlying JSF implementation, and then to Spring's 'business context' WebApplicationContext. This allows one to easily inject dependencies into one's JSF-managed beans.

FacesContextUtils:custom VariableResolver works well when mapping one's properties to beans in faces-config.xml, but at times one may need to grab a bean explicitly. The FacesContextUtils class makes this easy. It is similar to WebApplicationContextUtils, except that it takes a FacesContext parameter rather than a ServletContext parameter.

ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());

Q)What are the difference between Spring and EJB ?

have a look at the main important differences between the two:

1) Distributed Computing – If components in your web-container need to access remote components, then EJB provides in-build support for remote method calls. The EJB container manages all RMI-IIOP connections. Spring provides support for proxying remote calls via RMI, JAX-RPC etc.
2) Transaction Support – EJB by default uses the JTA manager provided by the EJB container and hence can support XA or distributed transactions. Spring does not have default support for distributed transactions, but it can plug in a JTA Transaction manager. Both EJB and Spring allows for declarative transaction demarcation. EJB uses deployment descriptor and Spring uses AOP.
3) Persistance – Entity Beans provide CMP and BMP strategies, but my personal experience with these options has been devastating. Entity Beans are too slow!!!.
Spring integrates with Hibernate, IBatis and also has good JDBC wrapper components (JdbcTemplate).
4) Security – EJB provides support for declarative security through the deployment descriptor. But again, this incurs a heavy performance penalty and I have rarely seen projects using EJB-container managed security.

Q)What is Java Server Faces (JSF) - Spring integration mechanism?

Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard JavaServer Faces managed beans mechanism. When asked to resolve a variable name, the following algorithm is performed:

Does a bean with the specified name already exist in some scope (request, session, application)? If so, return it

Is there a standard JavaServer Faces managed bean definition for this variable name? If so, invoke it in the usual way, and return the bean that was created.

Is there configuration information for this variable name in the Spring WebApplicationContext for this application? If so, use it to create and configure an instance, and return that instance to the caller.

If there is no managed bean or Spring definition for this variable name, return null instead.

BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.

As a result of this algorithm, you can transparently use either JavaServer Faces or Spring facilities to create beans on demand.

Q)What is Significance of JSF- Spring integration ?

Spring - JSF integration is useful when an event handler wishes to explicitly invoke the bean factory to create beans on demand, such as a bean that encapsulates the business logic to be performed when a submit button is pressed.

Q)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.

Q) What are ORM’s Spring supports ?

Spring supports the following ORM’s :
JPA (Java Persistence API)
JDO (Java Data Objects)

Q)How to integrate Spring and Hibernate ?

Spring and Hibernate can integrate using Spring’s SessionFactory called LocalSessionFactory. The integration process is of 3 steps.

Configure Hibernate mappings.
Configure Hibernate properties.
Wire dependant object to SessionFactory.

Q)What are the ways to access Hibernate using Spring ?

There are two ways to access Hibernate from Spring:

Through Hibernate Template.
Subclassing HibernateDaoSupport
Extending HibernateDaoSupport and Applying an AOP Interceptor

QWhat 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
Scopes a single bean definition to a single object instance per Spring IoC container.

Scopes a single bean definition to any number of object instances.

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 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.

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.

Q)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.

Q)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.

Q)What are the types of the transaction management Spring supports ?

Spring Framework supports:

Programmatic transaction management.
Declarative transaction management.

Q)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.

Q)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.

Q)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.

Q)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.

Q)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.

Q)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);

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