Struts: Important Questions with Answer

1. 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. The process() 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

2. What are the different kinds of actions in Struts?

The different kinds of actions in Struts are:

• ForwardAction
• IncludeAction
• DispatchAction
• LookupDispatchAction
• SwitchAction

3. 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:

>actionservlet-name>



org.apache.struts.action.ActionServlet





config



/WEB-INF/struts-config.xml,

/WEB-INF/struts-admin.xml,

/WEB-INF/struts-config-forms.xml





.....

4. What is DispatchAction?

The DispatchAction class is used to group related actions into one class. Using this class, you can have a method for each logical action compared than a single execute method. The DispatchAction dispatches to one of the logical actions represented by the methods. It picks a method to invoke based on an incoming request parameter. The value of the incoming parameter is the name of the method that the DispatchAction will invoke.

22.How to use DispatchAction?

To use the DispatchAction, follow these steps :

• Create a class that extends DispatchAction (instead of Action)
• In a new class, add a method for every function you need to perform on the service – The method has the same signature as the execute() method of an Action class.
• Do not override execute() method – Because DispatchAction class itself provides execute() method.
• Add an entry to struts-config.xml

23.What is the use of ForwardAction?

The ForwardAction class is useful when you’re trying to integrate Struts into an existing application that uses Servlets to perform business logic functions. You can use this class to take advantage of the Struts controller and its functionality, without having to rewrite the existing Servlets. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page. By using this predefined action, you don’t have to write your own Action class. You just have to set up the struts-config file properly to use ForwardAction.

24.What is IncludeAction?

The IncludeAction class is useful when you want to integrate Struts into an application that uses Servlets. Use the IncludeAction class to include another resource in the response to the request being processed.

25.What is the difference between ForwardAction and IncludeAction?

The difference is that you need to use the IncludeAction only if the action is going to be included by another action or jsp. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page.

26.What is LookupDispatchAction?

The LookupDispatchAction is a subclass of DispatchAction. It does a reverse lookup on the resource bundle to get the key and then gets the method whose name is associated with the key into the Resource Bundle.

27.What is the use of LookupDispatchAction?

LookupDispatchAction is useful if the method name in the Action is not driven by its name in the front end, but by the Locale independent key into the resource bundle. Since the key is always the same, the LookupDispatchAction shields your application from the side effects of I18N.

28.What is difference between LookupDispatchAction and DispatchAction?

The difference between LookupDispatchAction and DispatchAction is that the actual method that gets called in LookupDispatchAction is based on a lookup of a key value instead of specifying the method name directly.

29.What is SwitchAction?

The SwitchAction class provides a means to switch from a resource in one module to another resource in a different module. SwitchAction is useful only if you have multiple modules in your Struts application. The SwitchAction class can be used as is, without extending.

30.What if element has declaration with same name as global forward?

In this case the global forward is not used. Instead the element’s takes precendence.

31. What is DynaActionForm?

A specialized subclass of ActionForm that allows the creation of form beans with dynamic sets of properties (configured in configuration file), without requiring the developer to create a Java class for each type of form bean.

32.What are the steps need to use DynaActionForm?

Using a DynaActionForm instead of a custom subclass of ActionForm is relatively straightforward. You need to make changes in two places:

• In struts-config.xml: change your to be an org.apache.struts.action.DynaActionForm instead of some subclass of ActionForm

name="loginForm"type="org.apache.struts.action.DynaActionForm" >

name="userName" type="java.lang.String"/>

name="password" type="java.lang.String" />

import org.apache.struts.action.DynaActionForm;



public class DynaActionFormExample extends Action {

 public ActionForward execute(ActionMapping mapping, ActionForm form,

   HttpServletRequest request, HttpServletResponse response)

            throws Exception {             

  DynaActionForm loginForm = (DynaActionForm) form;

                ActionMessages errors = new ActionMessages();       

        if (((String) loginForm.get("userName")).equals("")) {

            errors.add("userName", new ActionMessage(

                            "error.userName.required"));

        }

        if (((String) loginForm.get("password")).equals("")) {

            errors.add("password", new ActionMessage(

                            "error.password.required"));

        }

33. What is the life cycle of ActionForm?

The lifecycle of ActionForm invoked by the RequestProcessor is as follows:

• Retrieve or Create Form Bean associated with Action
• "Store" FormBean in appropriate scope (request or session)
• Reset the properties of the FormBean
• Populate the properties of the FormBean
• Validate the properties of the FormBean
• Pass FormBean to Action