Java J2EE interview questions

The tag to allow front-end validation based on the xml in validation.xml. For example the code: generates the client side java script for the form "logonForm" as defined in the validation.xml file. The when added in the jsp file generates the client site validation script.

Can I setup Apache Struts to use multiple configuration files?

Yes Struts can use multiple configuration files. Here is the configuration example:
<servlet>
            <servlet-name>banking</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-authentication.xml,
                                           /WEB-INF/struts-help.xml</param-value>
            </init-param>
            <load-on-startup>1</load-on-startup>
</servlet>

How you will make available any Message Resources Definitions file to the Struts Framework Environment?

Message Resources Definitions file are simple .properties files and these files contains the messages that can be used in the struts project. Message Resources Definitions files can be added to the struts-config.xml file through tag.
Example:

What is Struts Flow?

Struts Flow is a port of Cocoon's Control Flow to Struts to allow complex workflow, like multi-form wizards, to be easily implemented using continuations-capable JavaScript. It provides the ability to describe the order of Web pages that have to be sent to the client, at any given point in time in an application. The code is based on a proof-of-concept Dave Johnson put together to show how the Control Flow could be extracted from Cocoon. (Ref: http://struts.sourceforge.net/struts-flow/index.html )

What are the difference between and ?

: This tag is used to output locale-specific text (from the properties files) from a MessageResources bundle.
: This tag is used to output property values from a bean. is a commonly used tag which enables the programmers to easily present the data.

What is LookupDispatchAction?

An abstract Action that dispatches to the subclass mapped execute method. This is useful in cases where an HTML form has multiple submit buttons with the same name. The button name is specified by the parameter property of the corresponding ActionMapping.

What do you understand by DispatchAction?

DispatchAction is an action that comes with Struts 1.1 or later, that lets you combine Struts actions into one class, each with their own method. The org.apache.struts.action.DispatchAction class allows multiple operation to mapped to the different functions in the same Action class.
For example:
A package might include separate RegCreate, RegSave, and RegDelete Actions, which just perform different operations on the same RegBean object. Since all of these operations are usually handled by the same JSP page, it would be handy to also have them handled by the same Struts Action.
A very simple way to do this is to have the submit button modify a field in the form which indicates which operation to perform.

SAVE
SAVE AS NEW
DELETE
Then, in the Action you can setup different methods to handle the different operations, and branch to one or the other depending on which value is passed in the dispatch field.
String dispatch = myForm.getDispatch();
if ("create".equals(dispatch)) { ...
if ("save".equals(dispatch)) { ...
The Struts Dispatch Action [org.apache.struts.actions] is designed to do exactly the same thing, but without messy branching logic. The base perform method will check a dispatch field for you, and invoke the indicated method. The only catch is that the dispatch methods must use the same signature as perform. This is a very modest requirement, since in practice you usually end up doing that anyway.
To convert an Action that was switching on a dispatch field to a DispatchAction, you simply need to create methods like this
public ActionForward create(
    ActionMapping mapping,
    ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response)
throws IOException, ServletException { ...
public ActionForward save(
    ActionMapping mapping,
    ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response)
throws IOException, ServletException { ...
Cool. But do you have to use a property named dispatch? No, you don't. The only other step is to specify the name of of the dispatch property as the "parameter" property of the action-mapping. So a mapping for our example might look like this:

path="/reg/dispatch"
type="app.reg.RegDispatch"
name="regForm"
scope="request"
validate="true"
parameter="dispatch"/>
If you wanted to use the property "o" instead, as in o=create, you would change the mapping to

path="/reg/dispatch"
type="app.reg.RegDispatch"
name="regForm"
scope="request"
validate="true"
parameter="o"/>
Again, very cool. But why use a JavaScript button in the first place? Why not use several buttons named "dispatch" and use a different value for each?
You can, but the value of the button is also its label. This means if the page designers want to label the button something different, they have to coordinate the Action programmer. Localization becomes virtually impossible.

Is struts threadsafe?Give an example?

Struts is not only thread-safe but thread-dependant. The response to a request is handled by a light-weight Action object, rather than an individual servlet. Struts instantiates each Action class once, and allows other requests to be threaded through the original object. This core strategy conserves resources and provides the best possible throughput. A properly-designed application will exploit this further by routing related operations through a single Action

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