Cannot get a RequestDispatcher

Question

I've read lots of similar questions and tryed all suggested methods for fixing the problem, however it's unsuccessfully. Now I really don't have any ideas what to do with this (localhost:8080/testWebApp/home):

HTTP Status 500 -
...    
exception

java.lang.NullPointerException
    test.web.servlet.TestServlet.doGet(TestServlet.java:37)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

I use maven 3.3.9 and tomcat7 7.0.70-1. My project directory has the following hierarchy:

webApp/
   pom.xml
      src/
         main/
            java/
               test/web/servlet/
                        TestServlet.java
         webapp/
            index.html
            WEB-INF/
               views/
                  home.jsp
               web.xml

Here is the TestServlet code:

package test.web.servlet;


import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletOutputStream;


@WebServlet(urlPatterns = { "/home"})

public class TestServlet extends HttpServlet {

    @Override    
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
    }

    public TestServlet() {
        super();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/WEB-INF/views/home.jsp");
        //The following attempts are unsuccessful too:
        //RequestDispatcher dispatcher = request.getRequestDispatcher("/home.jsp");
        //RequestDispatcher dispatcher = request.getRequestDispatcher("/WEB-INF/views/home.jsp");
        dispatcher.forward(request, response); // error (37 line)
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
}

Here is web.xml code:

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_4.dtd">

<web-app>

    <welcome-file-list>  
        <welcome-file>home</welcome-file>
        <welcome-file>index.html</welcome-file>
    </welcome-file-list>  

</web-app>

home.jsp code:

<%@ page language="java" contentType="text/html; charset=UTF-8"
  pageEncoding="UTF-8"%>
<!DOCTYPE html>    
<html>
    <head>
        <meta charset="UTF-8">
        <title>Home Page</title>
    </head>

    <body>    
<%--         <jsp:include page="main.jsp"></jsp:include> --%>

        <h3>Home</h3>
        <br><br>
        <b>You have the following options:</b>
        <ul>
            <li>Login</li>
        </ul>    
    </body>    
</html>

Some useful lines from pom.xml:

    <plugin>
        <groupId>org.apache.tomcat.maven</groupId> 
        <artifactId>tomcat7-maven-plugin</artifactId>
        <version>2.2</version>
        <configuration>
            <server>tomcat-7.0.70-1</server>
            <url>http://localhost:8080/manager/text</url>
            <path>/testWebApp</path>
        </configuration>
    </plugin>

Thank you for help!

If you're just asking about the `NullPointerException`, this is a [duplicate](/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it). What you should be asking is why the `RequestDispatcher` is null. — user207421, Sep 16 '16 at 00:43

score 3 · Answer 1 · answered Sep 15 '16 at 13:38

You cannot get a RequestDispatcher for arbitrary files in your application. The argument to getRequestDispatcher() must be a valid URL path for your application, not a relative file system Location. This is why the dispatcher is null.

If you want to have your JSPs residing under WEB-INF (which is a good idea), then you must create appropriate <servlet-mapping> elements for them.

score 0 · Answer 2 · edited May 23 '17 at 11:51

After deeper investigation of servlet documentation (especially mapping topic) I made some modifications of web.xml and TestServlet.java. It's important that:

The WEB-INF directory is not part of the public document tree of the application. No file contained in the WEB-INF directory can be served directly to a client by the container. In my case views folder is inside WEB-INF (for user access limitation from the outside).

So, it's need to add the following lines (web.xml):

...
<servlet>
    <servlet-name>home</servlet-name>
    <jsp-file>/WEB-INF/views/home.jsp</jsp-file>
    <init-param>
        <param-name>home</param-name>
        <param-value>Home Page</param-value>
    </init-param>
</servlet>

<servlet-mapping>
    <servlet-name>home</servlet-name>
    <url-pattern>/homepg</url-pattern>
</servlet-mapping>
...

And corrected TestServlet.java:

RequestDispatcher dispatcher = getServletContext().getRequestDispatcher("/homepg");

P.S. Thanks gsl for pointing in the proper direction!

Yeah, thx! :-) One more: Have a look at `ServletContext.getNamedDispatcher(name)`: This one gives a dispatcher based on the servlet **name**. You get the servlet by refering to its name "home"; then there is no need to defined a servlet-mapping, which is not needed anyway since you do not really want to create a URL space entry for it. — gsl, Sep 16 '16 at 06:54

Rohit Gaikwad · Answer 3 · 2016-09-16T05:50:10.977

0

You are dispatching the request to /WEB-INF/views/home.jsp url, but in your WEB-INF/views folder you have Home.jsp.

Just change the file name from Home.jsp to home.jsp and re-deploy the application, it should work fine.

Note: You are dispatching the request to a valid path i.e, /WEB-INF/views/home.jsp

edited Sep 16 '16 at 05:50

answered Sep 16 '16 at 05:36

Rohit Gaikwad

3,677
3
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Hm, when I got the error the first thing I tryed - was checking all the paths. Also in my case it was not the problem and I had views/home.jsp, not views/Home.jsp. Anyway, thank you for answer! – user3856196 Sep 16 '16 at 06:59
Sorry, it's somthing like a capital letter at the beginning of the line and then it really looks like a mistake. I'll edit this. – user3856196 Sep 16 '16 at 07:47

Cannot get a RequestDispatcher

3 Answers3