Spring FAQs-->4

Spring interview questions and answers

61 What is web module?

Spring comes with a full-featured MVC framework for building web applications. Although Spring can easily be integrated with other MVC frameworks, such as Struts, Spring’s MVC framework uses IoC to provide for a clean separation of controller logic from business objects. It also allows you to declaratively bind request parameters to your business objects. It also can take advantage of any of Spring’s other services, such as I18N messaging and validation.

62 What is a BeanFactory?

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.

63 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.

64 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.

65 .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.

66 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")

67 . 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.

68 . 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.

69 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.

70  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>

71.  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>

72 .  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.

73 . How can you override beans default lifecycle methods?

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

74 .  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.

75. What are the different types of bean injections?

There are two types of bean injections.

• By setter
• By constructor

76. What is Auto wiring?

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 autowire attribute of bean tag to an autowire type.

        <beans>
          <bean id="bar" class="com.act.Foo" Autowire=”autowire type”/>
        </beans>

77 . What are different types of Autowire types?

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

• byName
• byType
• constructor
• autodetect

78. 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.

79. 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.

80 . 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.