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Spring Interview Questions

1 . What is Spring Framework?

  • Spring is a lightweight inversion of control and aspect-oriented container framework.
    Spring is an open source framework created to address the complexity of enterprise application development.
    One of the main 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.

2 . 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.

3 . 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 strategy. Integration with Hibernate, JDO, and iBATIS: Spring provides best Integration services with Hibernate, JDO and iBATIS

4 . What is Inversion of Control (IOC)?

  • IoC provides services through which a component can access its dependencies and services for interacting with the dependencies throughout their life. In general, IoC can be decomposed into two subtypes:
    • Dependency Injection : With Dependency Lookup–style IoC, a component must acquire a reference to a dependency, Dependency Lookup comes in two types:
      • Dependency Pull
      • Contextualized Dependency Lookup (CDL)
    • Dependency Lookup : With Dependency Injection, the dependencies are injected into the component by the IoC container. Dependency Injection also has two common flavors in springs
      • Constructor Dependency Injection
      • Setter Dependency Injection
    From this definition, you can clearly see that when we are talking about DI, we are always talking about IoC, but when we are talking about IoC, we are not always talking about DI

5 . What Dependency Injection ?

  •     The basic concept of 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., 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, DI means an inversion of responsibility with regard to how an object obtains references to collaborating objects.

6 . What is Dependency Pull?

  • Dependency Pull is the most familiar type of IoC. In Dependency Pull, dependencies are pulled from a registry as required. For ex: code to access an EJB (2.1 or prior versions) has used Dependency Pull (i.e., via the JNDI API to look up an EJB component).

7 . What is Contextualized Dependency Lookup?

  • Contextualized Dependency Lookup (CDL) is similar, in some respects, to Dependency Pull, but in CDL, lookup is performed against the container that is managing the resource, not from some central registry, and it is usually performed at some set point.

8 . Injection vs. Lookup?

    • Using injection, you are free to use your classes completely decoupled from the IoC container that is supplying dependent objects with their collaborators manually, whereas with lookup, your classes are always dependent on the classes and interfaces defined by the container.
    • Another drawback with lookup is that it becomes very difficult to test your classes in isolation from the container. Using injection, testing your components is trivial, because you can simply provide the dependencies yourself using the appropriate constructor or setter

9 . What are the different 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.
    • Setter Injection (e.g. Spring): Dependencies are assigned through JavaBeans properties (ex: setter methods).
    • Interface Injection (e.g. Avalon): Injection is done through an interface.
    • Annotation based Injection

10 . What are the types of Dependency Injection Spring supports?

    • Setter Dependency Injection: In Setter Dependency Injection, the IoC container injects a component’s dependencies into the component via JavaBean-style setter methods. A component’s setters expose the set of dependencies the IoC container can manage.
    • Constructor Dependency Injection: Constructor Dependency Injection is Dependency Injection where a component’s dependencies are provided to it in its constructor(s). The component declares a constructor or a set of constructors taking as arguments its dependencies, and the IoC container passes the dependencies to the component when it instantiates it,

11 . Setter Injection vs. Constructor Injection

    • Constructor Injection is particularly useful when you absolutely must have an instance of the dependency class before your component is used. Many containers, Spring included, provide a mechanism for ensuring that all dependencies are defined when you use Setter Injection, but by using Constructor Injection, you assert the requirement for the dependency in a container-agnostic manner.
    • Setter Injection is useful in a variety of cases. If the component is exposing its dependencies to the container but is happy to provide its own defaults, then Setter Injection is usually the best way to accomplish this. Another benefit of Setter Injection is that it allows dependencies to be declared on an interface, although this is not as useful as you might first think. Setter injection also allows you to swap dependencies for a different implementation on the fly without creating a new instance of the parent component.
    • In general, setter-based injection is the best choice, because it has the least effect on your code’s usability in non-IoC settings. Constructor injection is a good choice when you want to ensure that dependencies are being passed to a component, but bear in mind that many containers provide their own mechanism for doing this with Setter Injection.

12 . What are the benefits of IOC (Dependency Injection)?

  • 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.

13 . How many modules are there in Spring? What are they?

  • Spring comprises of seven modules.
    • 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.

14 . 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.

15 . 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:
    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.

16 . 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

17 . Which is more used BeanFactory or ApplicationContext? Or Which one you prefer BeanFactory or ApplicationContext?

  • ApplicationContext. It covers almost all features which are there in BeanFactory and in addition also provides enterprise related features, which your application might require in future.

18 . 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 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.
    MyBean myBean = (MyBean) factory.getBean("myBean");

19 . What are important ApplicationContext implementations in spring framework?

    • ClassPathXmlApplicationContext - This context loads a context definition from an XML file located in the class path, treating context definition files as class path resources.
    • FileSystemXmlApplicationContext - This context loads a context definition from an XML file in the filesystem.
    • XmlWebApplicationContext - This context loads the context definitions from an XML file contained within a web application.

20 . Explain Bean lifecycle in Spring framework?

    • 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.

21 . What is bean wiring?

  • Combining together beans within the Spring container is known as bean wiring or wiring. When wiring beans, you should tell the container what beans are needed and how the container should use dependency injection to tie them together.

22 . 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>

    In the bean tag the id attribute specifies the bean name and the class attribute specifies the fully qualified class name.

23 . 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>

24 . 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.

25 . How can you override beans default lifecycle methods?

  • The bean tag has two more important attributes with which you can define your own custom initialisation 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>

26 . 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.

27 . What are the different types of bean injections?

  • There are two types of bean injections.
    By setter
    By constructor

28 . 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.

29 . 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.

30 . What do you mean by Auto Wiring?

  • The Spring container is able to auto wire 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 auto wiring functionality has five modes.
    byName
    byType
    constructor
    autodirect
    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 auto wire attribute of bean tag to an auto wire type.
    <beans>
    <bean id="bar" class="com.act.Foo" Autowire="autowire type"/>
    </beans>

31 . 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

32 . 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.

33 . 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.

34 . 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.

35 . 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.

36 . 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

37 . 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 the advice can be applied.

38 . 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.

39 . 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.

40 . 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.

41 . 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.

42 . What are ORM's Spring supports ?

  • Spring supports the following ORM's :
    • Hibernate
    • iBatis
    • JPA (Java Persistence API)
    • TopLink
    • JDO (Java Data Objects)
    • OJB

43 . 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

44 . 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

45 . 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:
    • 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 created 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.

46 . 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.

47 . 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.

48 . 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.

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

    • Compile Time
    • Classload Time
    • Runtime

50 . What are the different types of AutoProxying?

    • BeanNameAutoProxyCreator
    • DefaultAdvisorAutoProxyCreator
    • Metadata autoproxying