CODEWITHSUNDEEP
javajsp
Kramer786
Kramer786

Reputation: 1298

Why is the forward slash mandatory when forwarding from servlet to JSP?

When using a request dispatcher in a servlet to forward to a JSP why must the JSP be denoted with a forward slash like the following-:

    getServletContext().getRequestDispatcher("/foo.jsp").forward(request, response);

If I use it without the forward slash I get an exception in Tomcat.

But when I use request dispatcher for redirecting to servlets then I can omit the forward slash. The below code fragment works fine provided there is a servlet mapped to the url pattern-:

getServletContext().getRequestDispatcher("bar").forward(request, response);

I know that the / means the root of the web-app but why isn't it required for servlets but only for JSPs ? Servlets also belong to a particular web-app.

Upvotes: 6

Views: 1275

Answers (2)

IqbalHamid
IqbalHamid

Reputation: 2532

Your are mistaken to believe that the forward slash means root of the web app. It can sometimes mean that, but not always.

The forward slash '/' character is used in JSPs within links eg:

<a href="/foo/stuff.htm">Stuff page</a>

and in servlets by the RequestDispatcher.forward() and HTTPResponse.sendRedirect() methods for URL redirections.

It only has an effect when applied at the beginning of your redirection URL.

Here are the rules for how it is interpreted behind the scenes by the your application server:

  1. First of all: Please be aware that the redirection address is always CASE SENSITIVE -even in the domain segment of your redirection-URL. See my comments in example code below to see an illustration of this through examples of what will work and what will fail.

  2. If the redirection commences with 'http://', the ABSOLUTE path as specified, will be used in the redirection.

    Otherwise your redirection URL will be applied as a relative URL.

  3. If the redirection URL commences with a forward slash character '/', your application server is instructed to construct a URL RELATIVE to the web container!

    For example: relative to localhost:8080

    So the command...

    response.sendRedirect("/foo/stuff.htm")

    from inside a servlet, or

    <a href="/foo/stuff.htm">Stuff page</a>

    from inside a JSP, will take you to

    localhost:8080/foo/stuff.htm.

  4. The ABSENCE of a forward slash at the beginning of your redirection-url (together with the absence of a protocol signature) will instruct the app server to construct its url relative to the ORIGINAL REQUESTED URL! That is, the URL typed into the browser by a user at the client-side.

    It is important to be aware that this constructed URL is neither

    • relative to the domain

      nor

    • relative to the web container!

    Once again: the url constructed by the application server will be relative to the original url requested by the client!

    So for example: if a client provides the URL

    http://www.example.com/level1/level2/stuff.htm

    then the command...

    response.sendRedirect("foo/stuff.htm")

    from within a servlet or,

    <a href="foo/stuff.htm">Stuff page</a>

    from within a JSP, will redirect you to

    http://www.example.com/level1/level2/foo/stuff.htm

    


    // WILL NOT WORK!  Reason: Case sensitivity.
response.sendRedirect("/teluskolearnings/login.jsp");
    


    // WILL WORK!  Reason: Case sensitivity.
response.sendRedirect("/TeluskoLearnings/login.jsp");
    


    // Will redirect to localhost:8080/login.jsp as the forward slash tells app
// server to build the url RELATIVE TO THE APP SERVER.
// So you will be pointed to 'http://localhost:8080/login.jsp'.
// This is not what we want.
response.sendRedirect("/login.jsp");
    


    // Will redirect to localhost:8080/TeluskoLearnings/login.jsp
// as the ABSENCE of forward slash tells app server to build the url
// RELATIVE TO THE URL!
// So you will be pointed to
// 'http://localhost:8080/TeluskoLearnings/login.jsp'.
// This IS what we want.
response.sendRedirect("login.jsp");
    


    // Will redirect to localhost:8080/TeluskoLearnings/foo/login.jsp 
// (you can see the redirection in the address bar, even if you get a
// 404 - page not found) as the ABSENCE of forward slash (at the start) tells
// app server to build the URL RELATIVE TO THE REQUESTED URL!
// This also means that if the user entered
// 'http://localhost:8080/TeluskoLearnings/level1/level2/stuff"'
// he will be pointed to
// 'http://localhost:8080/TeluskoLearnings/level1/level2/foo/login.jsp'
// (provided of course, that "/level1/level2/stuff" is captured inside the
// urlPatterns parameter of the @WebServlet() annotation).
response.sendRedirect("foo/login.jsp");

SEE: https://www.safaribooksonline.com/library/view/head-first-servlets/9780596516680/ch04s27.html

Upvotes: 2

Ravi Thapa
Ravi Thapa

Reputation: 97

All the servlet objects are running at the same place in container but jsp goes to different place.

SERVLET LOCATION AFTER DEPLOYEMENT You will find all the servlets here apache-tomcat-7.0.55\webapps\Test\WEB-INF\classes\com\it\servlet

MainController.class

ABC.class

JSP LOCATION AFTER DEPLOYEMENT

apache-tomcat-7.0.55\work\Catalina\localhost\Test\org\apache\jsp

apiTester_jsp.class

Upvotes: 0

Related Questions