Java Spring Interview

1. What is Spring?

Spring is an open source development framework for Enterprise Java. The core features of the Spring Framework can be used in developing any Java application, but there are extensions for building web applications on top of the Java EE platform. Spring framework targets to make Java EE development easier to use and promote good programming practice

2. What are benefits of Spring Framework?

·         Lightweight: Spring is lightweight when it comes to size and transparency. The basic version of spring framework is around 2MB.

·         Inversion of control (IOC): Loose coupling is achieved in Spring, with the Inversion of Control technique. The objects give their dependencies instead of creating or looking for dependent objects.

·         Aspect oriented (AOP): Spring supports Aspect oriented programming and separates application business logic from system services.

·         Container: Spring contains and manages the life cycle and configuration of application objects.

·         MVC Framework: Spring’s web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks.

·         Transaction Management: Spring provides a consistent transaction management interface that can scale down to a local transaction and scale up to global transactions (JTA).

·         Exception Handling: Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO) into consistent, unchecked exceptions.

3. Which are the Spring framework modules?

The basic modules of the Spring framework are :

·         Core module

·         Bean module

·         Context module

·         Expression Language module

·         JDBC module

·         ORM module

·         OXM module

·         Java Messaging Service(JMS) module

·         Transaction module

·         Web module

·         Web-Servlet module

·         Web-Struts module

·         Web-Portlet modul

4. Explain the Core Container (Application context) module

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

5. BeanFactory – BeanFactory implementation example

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.

The most commonly used BeanFactory implementation is the XmlBeanFactory class.

6. XMLBeanFactory

The most useful one is org.springframework.beans.factory.xml.XmlBeanFactory, which loads its beans based on the definitions contained in an XML file. This container reads the configuration metadata from an XML file and uses it to create a fully configured system or application.

7. Explain the 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.

8. Explain the JDBC abstraction and DAO module

With the JDBC abstraction and DAO module we can be sure that we keep up the database code clean and simple, and prevent problems that result from a failure to close database resources. It provides a layer of meaningful exceptions on top of the error messages given by several database servers. It also makes use of Spring’s AOP module to provide transaction management services for objects in a Spring application.

9. Explain the 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 provides 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.

10. Explain the web module

The Spring web 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.

11. Explain the Spring MVC module

MVC framework is provided by Spring for building web applications. Spring can easily be integrated with other MVC frameworks, but Spring’s MVC framework is a better choice, since it uses IoC to provide for a clean separation of controller logic from business objects. With Spring MVC you can declaratively bind request parameters to your business objects.

12. 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.

13. What is Spring IoC container?

The Spring IoC is responsible for creating the objects,managing them (with dependency injection (DI)), wiring them together, configuring them, as also managing their complete lifecycle.

14. What are the benefits of IOC?

IOC or dependency injection minimizes the amount of code in an application. It makes easy to test applications, since no singletons or JNDI lookup mechanisms are required in unit tests. Loose coupling is promoted with minimal effort and least intrusive mechanism. IOC containers support eager instantiation and lazy loading of services.

15. What are the common implementations of the ApplicationContext?

The FileSystemXmlApplicationContext container loads the definitions of the beans from an XML file. The full path of the XML bean configuration file must be provided to the constructor.
The ClassPathXmlApplicationContext container also loads the definitions of the beans from an XML file. Here, you need to set CLASSPATH properly because this container will look bean configuration XML file in CLASSPATH.
The WebXmlApplicationContext: container loads the XML file with definitions of all beans from within a web application.

16. What is the difference between Bean Factory and ApplicationContext?

Application contexts provide a means for resolving text messages, a generic way to load file resources (such as images), they can publish events to beans that are registered as listeners. In addition, 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. The application context implements MessageSource, an interface used to obtain localized messages, with the actual implementation being pluggable.

17. What does a Spring application look like?

·         An interface that defines the functions.

·         The implementation that contains properties, its setter and getter methods, functions etc.,

·         Spring AOP

·         The Spring configuration XML file.

·         Client program that uses the function

18. What is Dependency Injection in Spring?

Dependency Injection, an aspect of Inversion of Control (IoC), is a general concept, and it can be expressed in many different ways.This concept says 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 (the IOC container) is then responsible for hooking it all up.

19. What are the different types of IoC (dependency injection)?

·         Constructor-based dependency injection: Constructor-based DI is accomplished when the container invokes a class constructor with a number of arguments, each representing a dependency on other class.

·         Setter-based dependency injection: Setter-based DI is accomplished by the container calling setter methods on your beans after invoking a no-argument constructor or no-argument static factory method to instantiate your bean.

20. Which DI would you suggest Constructor-based or setter-based DI?

You can use both Constructor-based and Setter-based Dependency Injection. The best solution is using constructor arguments for mandatory dependencies and setters for optional dependencies.

21. What are Spring beans?

The Spring Beans are Java Objects that form the backbone of a Spring application. They are instantiated, assembled, and managed by the Spring IoC container. These beans are created with the configuration metadata that is supplied to the container, for example, in the form of XML <bean/> definitions.

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.

22. What does a Spring Bean definition contain?

A Spring Bean definition contains all configuration metadata which is needed for the container to know how to create a bean, its lifecycle details and its dependencies.

23. How do you provide configuration metadata to the Spring Container?

There are three important methods to provide configuration metadata to the Spring Container:

·         XML based configuration file.

·         Annotation-based configuration

·         Java-based configuration

24. How do you define the scope of a bean?

When defining a <bean> in Spring, we can also declare a scope for the bean. It can be defined through the scope attribute in the bean definition. For example, when Spring has to produce a new bean instance each time one is needed, the bean’sscope attribute to be prototype. On the other hand, when the same instance of a bean must be returned by Spring every time it is needed, the the bean scope attribute must be set to singleton.

25. Explain the bean scopes supported by Spring

There are five scoped provided by the Spring Framework supports following five scopes:

·         In singleton scope, Spring scopes the bean definition to a single instance per Spring IoC container.

·         In prototype scope, a single bean definition has any number of object instances.

·         In request scope, a bean is defined to an HTTP request. This scope is valid only in a web-aware Spring ApplicationContext.

·         In session scope, a bean definition is scoped to an HTTP session. This scope is also valid only in a web-aware Spring ApplicationContext.

·         In global-session scope, a bean definition is scoped to a global HTTP session. This is also a case used in a web-aware Spring ApplicationContext.

The default scope of a Spring Bean is Singleton