Struts interview questions (Part-2)

21.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
DispatchAction Example »

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.
UseForwardAction 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 <action> element has <forward> declaration with same name as global forward?
In this case the global forward is not used. Instead the <action> element’s <forward>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 <form-bean> to be an org.apache.struts.action.DynaActionForm instead of some subclass of ActionForm

33.How to display validation errors on jsp page?
<html:errors/> tag displays all the errors. <html:errors/> iterates over ActionErrors request attribute.

34.What are the various Struts tag libraries?
The various Struts tag libraries are:
· HTML Tags
· Bean Tags
· Logic Tags
· Template Tags
· Nested Tags
· Tiles Tags

35.What is the use of <logic:iterate>?
<logic:iterate> repeats the nested body content of this tag over a specified collection.
<table border=1>
<logic:iterate id="customer" name="customers">
<tr>
<td><bean:write name="customer"
property="firstName"/></td>
<td><bean:write name="customer" property="lastName"/></td>
<td><bean:write name="customer" property="address"/></td>
</tr>
</logic:iterate>
</table>

36.What are differences between <bean:message> and <bean:write>
<bean:message>: is used to retrive keyed values from resource bundle. It also supports the ability to include parameters that can be
substituted for defined placeholders in the retrieved string.

<bean:message key="prompt.customer.firstname"/>
<bean:write>: is used to retrieve and print the value of the bean property. <bean:write> has no body.
<bean:write name="customer" property="firstName"/>

37.How the exceptions are handled in struts?
Exceptions in Struts are handled in two ways:
· Programmatic exception handling :
Explicit try/catch blocks in any code that can throw exception. It works well when custom value (i.e., of variable) needed
when error occurs.
· Declarative exception handling :You can either define <global-exceptions> handling tags in your struts-config.xml or define the exception handling tags within <action></action> tag. It works well when custom page needed when error occurs. This approach applies only to exceptions thrown by Actions.
<global-exceptions>
<exception key="some.key"
type="java.lang.NullPointerException"
path="/WEB-INF/errors/null.jsp"/>
</global-exceptions>
or
<exception key="some.key"
type="package.SomeException"
path="/WEB-INF/somepage.jsp"/>

38.What is difference between ActionForm and DynaActionForm?
· An ActionForm represents an HTML form that the user interacts with over one or more pages. You will provide properties to hold the state of the form with getters and setters to access them. Whereas, using DynaActionForm there is no need of providing properties to hold the state. Instead these properties and their type are declared in the struts-config.xml
· The DynaActionForm bloats up the Struts config file with the xml based definition. This gets annoying as the Struts Config file
grow larger.
· The DynaActionForm is not strongly typed as the ActionForm. This means there is no compile time checking for the form fields. Detecting them at runtime is painful and makes you go through redeployment.
· ActionForm can be cleanly organized in packages as against the flat organization in the Struts Config file.
· ActionForm were designed to act as a Firewall between HTTP and the Action classes, i.e. isolate and encapsulate the HTTP request parameters from direct use in Actions. With DynaActionForm, the property access is no different than using request.getParameter.
· DynaActionForm construction at runtime requires a lot of Java Reflection (Introspection) machinery that can be avoided.

39.How can we make message resources definitions file available to the Struts framework environment?
We can make message resources definitions file (properties file) available to Struts framework environment by adding this file to strutsconfig.
xml.
<message-resources
parameter="com.login.struts.ApplicationResources"/>

40.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