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

User · Answer

I think you will understand it through these examples below.

Source code structure:

/src/main/webapp/subdir/sample.jsp
/src/main/webapp/sample.jsp

Context is: TestApp
So the entry point: http://yourhostname-and-port/TestApp

Forward to RELATIVE path:

Using servletRequest.getRequestDispatcher("sample.jsp"):

http://yourhostname-and-port/TestApp/subdir/fwdServlet  ==> \subdir\sample.jsp
http://yourhostname-and-port/TestApp/fwdServlet ==> /sample.jsp

Using servletContext.getRequestDispatcher("sample.jsp"):

http://yourhostname-and-port/TestApp/subdir/fwdServlet ==> java.lang.IllegalArgumentException: Path sample.jsp does not start with a "/" character
http://yourhostname-and-port/TestApp/fwdServlet ==> java.lang.IllegalArgumentException: Path sample.jsp does not start with a "/" character

Forward to ABSOLUTE path:

Using servletRequest.getRequestDispatcher("/sample.jsp"):

http://yourhostname-and-port/TestApp/subdir/fwdServlet  ==> /sample.jsp
http://yourhostname-and-port/TestApp/fwdServlet ==> /sample.jsp

Using servletContext.getRequestDispatcher("/sample.jsp"):

http://yourhostname-and-port/TestApp/subdir/fwdServlet ==> /sample.jsp
http://yourhostname-and-port/TestApp/fwdServlet ==> /sample.jsp

User · Answer

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

User · Answer

If you use an absolute path such as    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

User · Answer

request getRequestDispatcher    url     means the dispatch is relative to the current HTTP request Means this is for chaining two servlets with in the same web application Example  RequestDispatcher reqDispObj   request getRequestDispatcher   home jsp      getServletContext   getRequestDispatcher    url     means the dispatch is relative to the root of the ServletContext Means this is for chaining two web applications with in the same server two different servers  Example  RequestDispatcher reqDispObj   getServletContext   getRequestDispatcher   ContextRoot home jsp

User · Answer

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

User · Answer

The request method getRequestDispatcher   can be used for referring to local servlets within single webapp   Servlet context based getRequestDispatcher   method can used of referring servlets from other web applications deployed on SAME server

[java] ServletContext.getRequestDispatcher() vs ServletRequest.getRequestDispatcher()

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