Task overview: Assembling applications using remote request dispatcher

Remote request dispatcher (RRD) is a pluggable extension to the web container which allows application frameworks, servlets and JavaServer Pages (JSP) to include content from outside the currently executing resource's Java™ Virtual Machine (JVM) as part of the response sent to the client.

Before you begin

You must have WebSphere® Application Server Network Deployment installed to use remote request dispatcher function. You should also familiarize yourself the limitations of remote request dispatcher. See article, Remote request dispatcher considerations for details.

Procedure

Install enterprise application files with the console.
Configure the sending of include requests between the application and remote resources.
- Configure web applications to dispatch remote includes.
- Configure web applications to service remote includes.

Optional: Modify your application to locate resources located in two different contexts using the servlet programming model.

The Servlet Programming Model for including resources remotely does not require you to use any non-Java Platform, Enterprise Edition (Java EE) Servlet Application Programming Interfaces (APIs). The remote request dispatcher (RRD) component follows the same rules to obtain a ServletContext and a remote resource. By using JavaServer Pages standard tag library (JSTL), your application is further removed from obtaining a ServletContext object or RequestDispatcher that is required in the framework example in the following step because the JSTL custom tag does this implicitly. Study the following example of a sample JavaServer Pages application to learn how to locate resources that are in two different contexts, investments and banking.

<HEAD>
<%@ page
language="java"
contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8059-1"
isELIgnored="false"
%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" $>
</HEAD>
<BODY>

<%--

Programming example using JavaServer Pages and JavaSever Pages
Standard Tag Library (JSTL).
JSTL provides a custom tag to import contents (in servlet and JSP
terms include) in the scope of the same request from outside of
the current web module context by specifying a context parameter.

JSTL restriction: The web module that is imported 
must run inside of the same JVM as the calling resource
if imported URL is not fully qualified.

RRD extends this functionality by permitting the web module to 
be located within the scope of the current WebSphere Application Server
core group versus the scope of the JVM.
--%>


<hr size="5"/>
<%--		Include resource investmentSummary.jsp located in the 
		web application with context root of /investments. --%>

<c:import url="investmentSummary.jsp" context="/investments"/>

<hr size="5"/>
<%--		Include resource accountSummary.jsp located in the 
		web application	with context root of /banking. --%>

<c:import url="accountSummary.jsp" context="/banking"/>

<hr size="5"/>

</BODY>
</HTML>

Optional: Modify your application to locate resources located in two different contexts using the framework programming model.

The Framework Programming Model for including resources remotely does not require you to use any non- Java Platform, Enterprise Edition (Java EE) Servlet Application Programming Interfaces (APIs). When a request is initiated for a ServletContext name that is not presently running inside of the current web container, the remote request dispatcher (RRD) component returns a ServletContext object that can locate a resource that exists anywhere inside a WebSphere Application Sever WebSphere Application Server Network Deployment environment provided that the resource exists and RRD is enabled for that ServletContext object. Study the following sample framework snippet that demonstrates how to locate resources located in two different contexts, investments and banking.

/*
Programming example using a generic framework.
Servlet Specification provides an API to obtain 
a servlet context in the scope of the same request
different from the current web module context by
specifying a context parameter.

Servlet Specification restriction: The web module that obtain
must run inside of the same JVM as the calling resource.

RRD extends this functionality by permitting the web module to be located
within the scope of the current WebSphere Application Server core group 
versus the scope of the JVM.

*/

protected void frameworkCall (ServletContext context, HttpServletRequest request, HttpServletResponse response) 
							throws ServletException, IOException(

			PrintWriter writer = response.getWriter();

			writer.write("<HTML>");
			writer.write("<HEAD>");
			writer.write("</HEAD>");
			writer.write("<BODY>");
			writer.write("<hr size=\"5/">);

			//Include resource investmentSummary.jsp located in web application
			//with context root of /investments.
			RequestDispatcher rd = getRequestDispatcher ( context, "/investments", "/investmentSummary.jsp");
			rd.include(request, response);

			writer.write("<hr size=\"5/">);

			//Include resource accountSummary.jsp located in web application
			//with context root of /banking.
			rd = getRequestDispatcher ( context, "/banking", "/accountSummary.jsp");
			rd.include(request, response);

			writer.write("</BODY>");
			writer.write("</HTML>");
}
private RequestDispatcher getRequestDispatcher (ServletContext context, String contextName, String resource) {
			return context.getContext(contexName).getRequestDispatcher(resource);
}

Results

After enabling at least one enterprise application to dispatch remote includes and at least one enterprise application to service remote includes, RRD is now enabled.

What to do next

Restart the modified applications if already installed or start newly installed applications to enable RRD on each application.