ServletContext.getRequestDispatcher() vs ServletRequest.getRequestDispatcher()

Question

why

getRequestDispatcher(String path) of the ServletRequest interface cannot extend outside the current servlet context

where as

getRequestDispatcher(String path) of the ServletContext can use the getContext(String uripath) method to obtain RequestDispatcher for resources in foreign contexts.

and how??

Please help

Answer 1

I would think that your first question is simply a matter of scope. The ServletContext is a much more broad scoped object (the whole servlet context) than a ServletRequest, which is simply a single request. You might look to the Servlet specification itself for more detailed information.

As to how, I am sorry but I will have to leave that for others to answer at this time.

Answer 2

If you use absolute path ("/index.jsp"), there is no difference.

If you use relative path, you must use HttpServletRequest.getRequestDispatcher(). ServletContext.getRequestDispatcher() doesn't allow it.

For example, if you receive your request on http://example.com/myapp/subdir,

    RequestDispatcher dispatcher = 
        request.getRequestDispatcher("index.jsp);
    dispatcher.forward( request, response );

Will forward the request to the page http://example.com/myapp/subdir/index.jsp.

In any case, you can't forward request to a resource outside of the context.

Answer 3

Context is stored at the application level scope where as request is stored at page level i.e to say

Web Container brings up the applications one by one and run them inside its JVM. It stores a singleton object in its jvm where it registers anyobject that is put inside it.This singleton is shared across all applications running inside it as it is stored inside the JVM of the container itself.

However for requests, the container creates a request object that is filled with data from request and is passed along from one thread to the other (each thread is a new request that is coming to the server), also request is passed to the threads of same application.