How can a RequestDispatcher call a servlet in another web application?

[Yorck Zhou]

in the servlet specification 2.3 there is such a statement:

To illustrate this requirement with an example: if a servlet uses the RequestDispatcher to call a servlet in another web application, any sessions created for and visible to the callee servlet must be different from those visible to the calling servlet.

[Anthony Watson]

Use the code below to get the servlet context reference. From there, you can retrieve an appropriate RequestDispatcher.

this.getServletContext().getContext(uripath)

[Yorck Zhou]

Thanks Anthony!
But when I tried the following fragment code in the Tomcat 4.1. It return a NullpointerException. Is it a bug of Tomcat 4.1?

try{
ServletContext rootContext = getServletContext().getContext("http://localhost:8080/");
System.out.println( ( rootContext.getAttribute("root") ).toString() );
}catch(Exception e){
System.out.println(e);
}

[Nicholas Cheung]

You need to specify the context path of your Web application, not the URL that accessing your website.

Nick

[Yorck Zhou]

Yes, I have also tried a uri as an argument of the getContext() method, but it is still return a NullpointerException!

In the servlet API, I found the following statement about the getContext():

In a security conscious environment, the servlet container may return null for a given URL.

So, should make any change in the Tomcat to make it work?