Interview Questions and Answers

Ques 1. 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.

Ques 2. 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.
• 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.
• 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.
• JDBC Exception Handling: The JDBC abstraction layer of the Spring offers a meaningful exception hierarchy, which simplifies the error handling.

Ques 3. What are the advantages of Spring framework?

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.

Ques 4. What is 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:

Ques 5. What is 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.

Ques 6. 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.

• no
• byName
• byType
• constructor
• autodetect

Ques 7. What is IOC or inversion of control?

As the name implies Inversion of control means now we have inverted the control of creating the object from our own using new operator to container or framework. Now it's the responsibility of container to create object as required.

Ques 8. Explain Bean-LifeCycle.

Spring framework is based on IOC so we call it as IOC container also So Spring beans reside inside the IOC container. Spring beans are nothing but Plain old java object (POJO).

Ques 9. What are the different modules in Spring framework?

• The Core container module
• Application context module
• AOP module (Aspect Oriented Programming)
• JDBC abstraction and DAO module
• O/R mapping integration module (Object/Relational)
• Web module
• MVC framework module

Ques 10. what is Bean Factory, have you used XMLBeanFactory?

BeanFactory is factory Pattern which is based on IOC design principles. It is used to make a clear separation between application configuration and dependency from actual code.

Ques 11. Please describe the basic modules of Spring Framework.

Spring comprises of seven modules. They are..

► 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.

Ques 12. What are the types of Dependency Injection Spring supports?

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

Ques 13. What is the difference between Bean Factory and Application Context?

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.

Ques 14. 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.

Ques 15. 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.

Ques 16. 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.

Ques 17. 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.

Ques 18. What is the Core container module?

This module is provides the fundamental functionality of the spring framework. In this module BeanFactory is the heart of any spring-based application. The entire framework was built on the top of this module. This module makes the Spring container.

Ques 19. What is Application context module?

The Application context module makes spring a framework. This module extends the concept of BeanFactory, providing support for internationalization (I18N) messages, application lifecycle events, and validation. This module also supplies many enterprise services such JNDI access, EJB integration, remoting, and scheduling. It also provides support to other framework.

Ques 20. What is AOP module?

The AOP module is used for developing aspects for our Spring-enabled application. Much of the support has been provided by the AOP Alliance in order to ensure the interoperability between Spring and other AOP frameworks. This module also introduces metadata programming to Spring. Using Spring's metadata support, we will be able to add annotations to our source code that instruct Spring on where and how to apply aspects.

Ques 21. 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.

Ques 22. 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.

Ques 23. 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.

Ques 24. 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.

Ques 25. 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.

Ques 26. 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.

Ques 27. 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.

Ques 28. Explain Bean lifecycle in Spring framework?

1. The spring container finds the bean�s definition from the XML file and instantiates the bean.
2. Using the dependency injection, spring populates all of the properties as specified in the bean definition.
3. If the bean implements the BeanNameAware interface, the factory calls setBeanName() passing the bean�s ID.
4. If the bean implements the BeanFactoryAware interface, the factory calls setBeanFactory(), passing an instance of itself.
5. If there are any BeanPostProcessors associated with the bean, their post- ProcessBeforeInitialization() methods will be called.
6. If an init-method is specified for the bean, it will be called.
7. Finally, if there are any BeanPostProcessors associated with the bean, their postProcessAfterInitialization() methods will be called.

Ques 29. 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.

Ques 30. 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.

Ques 31. 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.

Ques 32. 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.

Ques 33. What are the different types of bean injections?

There are two types of bean injections.

1. By setter
2. By constructor

Ques 34. What are different types of Autowire types?

There are four different types by which autowiring can be done.

► byName
► byType
► constructor
► autodetect

Ques 35. 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.

Ques 36. 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.

Ques 37. 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.

Ques 38. 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.

Ques 39. 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.

Ques 40. 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 anyadvice that is being applied.

Ques 41. 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.

Ques 42. 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 into the target object at the specified joinpoints.

Ques 43. What are the different points where weaving can be applied?

► Compile Time
► Classload Time
► Runtime

Ques 44. 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

Ques 45. What are the different types of AutoProxying?

► BeanNameAutoProxyCreator
► DefaultAdvisorAutoProxyCreator
► Metadata autoproxying

Ques 46. What are different modules in spring?

spring have seven core modules
1. The Core container module
2. Application context module
3. AOP module (Aspect Oriented Programming)
4. JDBC abstraction and DAO module
5. O/R mapping integration module (Object/Relational)
6. Web module
7. MVC framework module

Ques 47. What is difference between singleton and prototype bean?

Basically a bean has scopes which defines their existence on the application

Singleton: means single bean definition to a single object instance per Spring IOC container.

Prototype: means a single bean definition to any number of object instances.

Whatever beans we 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.

<bean id="createNewStock" class="springexample.stockMarket.CreateNewStockAccont" singleton="false">
<property name="newBid"/>
</bean>

Ques 48. What is AOP?

The core construct of AOP is the aspect, which encapsulates behaviors affecting multiple classes into reusable modules. AOP is a programming technique that allows developer to modularize crosscutting concerns, that cuts across the typical divisions of responsibility, such as logging and transaction management. Spring AOP, aspects are implemented using regular classes or regular classes annotated with the @Aspect annotation.

Ques 49. Explain Advice?

It�s an implementation of aspect; advice is inserted into an application at join points. Different types of advice include �around,� �before� and �after� advice.

Ques 50. How do you setup LDAP Authentication using Spring Security?

Spring provides out of the box support to connect Windows Active directory for LDAP authentication and with few configuration in Spring config file you can have this feature enable.

Ques 51. What type of transaction Management Spring support?

transaction management is a complex concept and not every developer familiar with it. Transaction management is critical in any applications that will interact with the database. The application has to ensure that the data is consistent and the integrity of the data is maintained. Two type of transaction management is supported by spring

1. Programmatic transaction management
2. Declarative transaction management.

Ques 52. How do you control concurrent Active session using Spring Security?

You can easily control How many active session a user can have with a Java application by using Spring Security.

In fact is all declarative and no code is require to enable concurrent session disable functionality. You will need to include following xml snippet in your Spring Security Configuration file mostly named as applicaContext-security.xml. Here is sample spring security Example of limiting user session in Java web application:

<session-management invalid-session-url="/logout.html">
<concurrency-control max-sessions="1" error-if-maximum-exceeded="true" />
</session-management>

As you see you can specify how many concurrent session per user is allowed, most secure system like online banking portals allow just one authenticate session per user. You can even specify a URL where user will be taken if they submit an invalid session identifier can be used to detect session timeout. Session-management element is used to capture session related stuff. Max-session specify how many concurrent authenticated session is allowed and if error-if-maximum-exceeded set to true it will flag error if user tries to login into another session.

Ques 53. What is layered architecture in spring?

Spring is one-stop shop for all your enterprise applications, however, Spring is modular, layered, allowing you to pick and choose which modules are applicable to you, without having to bring in the rest.