Struts FAQs-->1

Struts Interview Questions and Answers

1.What is MVC?

Model-View-Controller (MVC) is a design pattern put together to help control change. MVC decouples interface from business logic and data.

·         Model : The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller.

·         View: The view provides the presentation of the model. It is the look of the application. The view can access the model getters, but it has no knowledge of the setters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur.

·         Controller:The controller reacts to the user input. It creates and sets the model.

2.What is a framework?

A framework is made up of the set of classes which allow us to use a library in a best possible way for a specific requirement.

3.What is Struts framework?

Struts framework is an open-source framework for developing the web applications in Java EE, based on MVC-2 architecture. It uses and extends the Java Servlet API. Struts is robust architecture and can be used for the development of application of any size. Struts framework makes it much easier to design scalable, reliable Web applications with Java.

4.What are the components of Struts?

Struts components can be categorize into Model, View and Controller:

• Model: Components like business logic /business processes and data are the part of model.
• View: HTML, JSP are the view components.
• Controller: Action Servlet of Struts is part of Controller components which works as front controller to handle all the requests.

5.What are the core classes of the Struts Framework?

Struts is a set of cooperating classes, servlets, and JSP tags that make up a reusable MVC 2 design.

• JavaBeans components for managing application state and behavior.
• Event-driven development (via listeners as in traditional GUI development).
• Pages that represent MVC-style views; pages reference view roots via the JSF component tree.

6.What is ActionServlet?

ActionServlet is a simple servlet which is the backbone of all Struts applications. It is the main Controller component that handles client requests and determines which Action will process each received request. It serves as an Action factory – creating specific Action classes based on user’s request.

7.What is role of ActionServlet?

ActionServlet performs the role of Controller:

• Process user requests
• Determine what the user is trying to achieve according to the request
• Pull data from the model (if necessary) to be given to the appropriate view,
• Select the proper view to respond to the user
• Delegates most of this grunt work to Action classes
• Is responsible for initialization and clean-up of resources

8.What is the ActionForm?

ActionForm is javabean which represents the form inputs containing the request parameters from the View referencing the Action bean.

9.What are the important methods of ActionForm?

The important methods of ActionForm are : validate() & reset().

10.Describe validate() and reset() methods ?

validate() : Used to validate properties after they have been populated; Called before FormBean is handed to Action. Returns a collection of ActionError as ActionErrors. Following is the method signature for the validate() method.

public ActionErrors validate(ActionMapping mapping,HttpServletRequest request)

reset(): reset() method is called by Struts Framework with each request that uses the defined ActionForm. The purpose of this method is to reset all of the ActionForm's data members prior to the new request values being set. 

public void reset() {}

11.What is ActionMapping?

Action mapping contains all the deployment information for a particular Action bean. This class is to determine where the results of the Action will be sent once its processing is complete.

12.How is the Action Mapping specified ?

We can specify the action mapping in the configuration file called struts-config.xml. Struts framework creates ActionMappingobject from <ActionMapping> configuration element of struts-config.xml file

<action-mappings>
 <action path="/submit"
        type="submit.SubmitAction"
         name="submitForm"
         input="/submit.jsp"
         scope="request"
         validate="true">
  <forward name="success" path="/success.jsp"/>
  <forward name="failure" path="/error.jsp"/>
 </action>
</action-mappings>

13.What is role of Action Class?

An Action Class performs a role of an adapter between the contents of an incoming HTTP request and the corresponding business logic that should be executed to process this request.

14.In which method of Action class the business logic is executed ?

In the execute() method of Action class the business logic is executed.

public ActionForward execute( 

            ActionMapping mapping,
             ActionForm form,
             HttpServletRequest request,
             HttpServletResponse response)
          throws Exception ;

execute() method of Action class:

• Perform the processing required to deal with this request
• Update the server-side objects (Scope variables) that will be used to create the next page of the user interface
• Return an appropriate ActionForward object

15.What design patterns are used in Struts?

Struts is based on model 2 MVC (Model-View-Controller) architecture. Struts controller uses the command design pattern and the action classes use the adapter design pattern. Theprocess() method of the RequestProcessor uses the template method design pattern. Struts also implement the following J2EE design patterns.

• Service to Worker
• Dispatcher View
• Composite View (Struts Tiles)
• Front Controller
• View Helper
• Synchronizer Token

16.Can we have more than one struts-config.xml file for a single Struts application?

Yes, we can have more than one struts-config.xml for a single Struts application. They can be configured as follows:

<servlet>
<servlet-name>action</servlet-name>   
  <servlet-class>
        org.apache.struts.action.ActionServlet
  </servlet-class>
<init-param>
  <param-name>config</param-name>
  <param-value>
     /WEB-INF/struts-config.xml,              
     /WEB-INF/struts-admin.xml,
     /WEB-INF/struts-config-forms.xml      
  </param-value>
</init-param>
.....
<servlet>

17.What is the directory structure of Struts application?

The directory structure of Struts application :

18.What is the difference between session scope and request scope when saving formbean ?

when the scope is request,the values of formbean would be available for the current request.
when the scope is session,the values of formbean would be available throughout the session.