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11. 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

12. 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.

13. 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.

14.  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.

15. 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.

16. 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
  • autodirect

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

18. 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.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
   "http://www.springframework.org/dtd/spring-beans.dtd">

<faces-config>
   <application>
      <variable-resolver>
         org.springframework.web.jsf.DelegatingVariableResolver
      </variable-resolver>
   </application>
</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());

19. 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.