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Q1: What is ActionServlet?
A: The class org.apache.struts.action.ActionServlet is the called the
ActionServlet. In the the Jakarta Struts Framework this class plays the role of
controller. All the requests to the server goes through the controller.
Controller is responsible for handling all the requests.
Q2: How you will make available any Message Resources
Definitions file to the Struts Framework Environment?
A: 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
<message-resources /> tag.
Example:
<message-resources parameter="MessageResources" />
Q3: What is Action Class?
A: The Action is part of the controller. The purpose of Action Class is to
translate the HttpServletRequest to the business logic. To use the Action, we
need to Subclass and overwrite the execute() method. The
ActionServlet (commad) passes the parameterized class to Action Form using the
execute() method. There should be no database interactions in the action. The
action should receive the request, call business objects (which then handle
database, or interface with J2EE, etc) and then determine where to go next. Even
better, the business objects could be handed to the action at runtime (IoC
style) thus removing any dependencies on the model. The return type
of the execute method is ActionForward which is used by the Struts Framework to
forward the request to the file as per the value of the returned ActionForward
object.
Q4: Write code of any Action Class?
A: Here is the code of Action Class that returns the ActionForward
object.
TestAction.java
package roseindia.net;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
public class TestAction extends Action
{
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception{
return mapping.findForward("testAction");
}
}
Q5: What is
ActionForm?
A: An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm. ActionForm maintains the
session state for web application and the ActionForm object is automatically
populated on the server side with data entered from a form on the client side.
Q6: What is Struts Validator Framework?
A: Struts Framework provides the functionality to validate the form data.
It can be use to validate the data on the users browser as well as on the
server side. Struts Framework emits the java scripts and it can be used
validate the form data on the client browser. Server side validation of form
can be accomplished by sub classing your From Bean with
DynaValidatorForm class.
The Validator framework was developed by David Winterfeldt
as third-party add-on to Struts. Now the Validator framework is a part of
Jakarta Commons project and it can be used with or without Struts. The
Validator framework comes integrated with the Struts Framework and can be used
without doing any extra settings.
Q7. Give the Details of XML files used in Validator
Framework?
A: The Validator Framework uses two XML configuration files
validator-rules.xml and validation.xml. The
validator-rules.xml defines the standard validation routines, these are
reusable and used in validation.xml. to define the form specific
validations. The validation.xml defines the validations applied to a
form bean.
Q8. How you will display validation fail errors on jsp
page?
A: Following tag displays all the errors:
<html:errors/>
Q9. How you will enable front-end validation based on the
xml in validation.xml?
A: The <html:javascript> tag to allow front-end validation based on
the xml in validation.xml. For example the code: <html:javascript
formName="logonForm" dynamicJavascript="true" staticJavascript="true" />
generates the client side java script for the form "logonForm" as defined in the
validation.xml file. The <html:javascript> when added in the jsp file
generates the client site validation script.
Question10: What is RequestProcessor and
RequestDispatcher?
Answer: The controller is responsible for intercepting and translating
user input into actions to be performed by the model. The controller is
responsible for selecting the next view based on user input and the outcome of
model operations. The Controller receives the request from the browser, invoke a
business operation and coordinating the view to return to the client.
The controller is implemented by a java servlet, this servlet is centralized
point of control for the web application. In struts framework the controller
responsibilities are implemented by several different components like
The ActionServlet Class
The RequestProcessor Class
The Action Class
The ActionServlet extends the javax.servlet.http.httpServlet class. The
ActionServlet class is not abstract and therefore can be used as a concrete
controller by your application.
The controller is implemented by the ActionServlet class. All incoming requests
are mapped to the central controller in the deployment descriptor as follows.
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
</servlet>
All request URIs with the pattern *.do are mapped to this servlet in the
deployment descriptor as follows.
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
<url-pattern>*.do</url-pattern>
A request URI that matches this pattern will have the following form.
http://www.my_site_name.com/mycontext/actionName.do
The preceding mapping is called extension mapping, however, you can also specify
path mapping where a pattern ends with /* as shown below.
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>/do/*</url-pattern>
<url-pattern>*.do</url-pattern>
A request URI that matches this pattern will have the following form.
http://www.my_site_name.com/mycontext/do/action_Name
The class org.apache.struts.action.requestProcessor process the request
from the controller. You can sublass the RequestProcessor with your own version
and modify how the request is processed.
Once the controller receives a client request, it delegates the handling of the
request to a helper class. This helper knows how to execute the business
operation associated with the requested action. In the Struts framework this
helper class is descended of org.apache.struts.action.Action class. It acts as a
bridge between a client-side user action and business operation. The Action
class decouples the client request from the business model. This decoupling
allows for more than one-to-one mapping between the user request and an action.
The Action class also can perform other functions such as authorization, logging
before invoking business operation. the Struts Action class contains several
methods, but most important method is the execute() method.
public ActionForward execute(ActionMapping mapping,
ActionForm
form, HttpServletRequest request, HttpServletResponse
response) throws
Exception;
The execute() method is called by the controller when a request is received from
a client. The controller creates an instance of the Action class if one doesn?t
already exist. The strut framework will create only a single instance of each
Action class in your application.
Action are mapped in the struts configuration file and this configuration is
loaded into memory at startup and made available to the framework at runtime.
Each Action element is represented in memory by an instance of the
org.apache.struts.action.ActionMapping class . The ActionMapping object contains
a path attribute that is matched against a portion of the URI of the incoming
request.
<action>
path= "/somerequest"
type="com.somepackage.someAction"
scope="request"
name="someForm"
validate="true"
input="somejsp.jsp"
<forward name="Success" path="/action/xys"
redirect="true"/>
<forward name="Failure" path="/somejsp.jsp"
redirect="true"/>
</action>
Once this is done the controller should determine which view to return to the
client. The execute method signature in Action class has a return type
org.apache.struts.action.ActionForward class. The ActionForward class represents
a destination to which the controller may send control once an action has
completed. Instead of specifying an actual JSP page in the code, you can
declaratively associate as action forward through out the application. The
action forward are specified in the configuration file.
<action>
path= "/somerequest"
type="com.somepackage.someAction"
scope="request"
name="someForm"
validate="true"
input="somejsp.jsp"
<forward name="Success" path="/action/xys"
redirect="true"/>
<forward name="Failure" path="/somejsp.jsp"
redirect="true"/>
</action>
The action forward mappings also can be specified in a global section,
independent of any specific action mapping.
<global-forwards>
<forward name="Success" path="/action/somejsp.jsp" />
<forward name="Failure" path="/someotherjsp.jsp" />
</global-forwards>
public interface RequestDispatcher
Defines an object that receives requests from the client and sends them to any
resource (such as a servlet, HTML file, or JSP file) on the server. The servlet
container creates the RequestDispatcher object, which is used as a wrapper
around a server resource located at a particular path or given by a particular
name.
This interface is intended to wrap servlets, but a servlet container can create
RequestDispatcher objects to wrap any type of resource.
getRequestDispatcher
public RequestDispatcher
getRequestDispatcher(java.lang.String path)
Returns a RequestDispatcher object that acts as a wrapper for the resource
located at the given path. A RequestDispatcher object can be used to forward a
request to the resource or to include the resource in a response. The resource
can be dynamic or static.
The pathname must begin with a "/" and is interpreted as relative to the current
context root. Use getContext to obtain a RequestDispatcher for resources in
foreign contexts. This method returns null if the ServletContext cannot return a
RequestDispatcher.
Parameters:
path - a String specifying the pathname to the resource
Returns:
a RequestDispatcher object that acts as a wrapper for the
resource at the specified path
See Also:
RequestDispatcher, getContext(java.lang.String)
getNamedDispatcher
public RequestDispatcher
getNamedDispatcher(java.lang.String name)
Returns a RequestDispatcher object that acts as a wrapper for the named servlet.
Servlets (and JSP pages also) may be given names via server administration or
via a web application deployment descriptor. A servlet instance can determine
its name using ServletConfig.getServletName().
This method returns null if the ServletContext cannot return a RequestDispatcher
for any reason.
Parameters:
name - a String specifying the name of a servlet to
wrap
Returns:
a RequestDispatcher object that acts as a wrapper for the
named servlet
See Also:
RequestDispatcher, getContext(java.lang.String),
ServletConfig.getServletName()
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