设置JNDI DataSource时出错

Question

我是从Java开始的。我正在按照使用Tomcat设置JNDI DataSource的教程，但我无法实现它。我总是得到相同的错误，错误500.例外是：java.lang.NullPointerException。

错误是：

HTTP Status 500 - 

type Exception report

message 

description The server encountered an internal error that prevented it from fulfilling this request.

exception
java.lang.NullPointerException
    demo.DatasourceDemo.doGet(DatasourceDemo.java:60)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:618)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

note The full stack trace of the root cause is available in the Apache Tomcat/8.0.15 logs.

Apache Tomcat/8.0.15

我的web.xml看起来像：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:web="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd http://xmlns.jcp.org/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.4">
  <description>MySQL Test App</description>
  <resource-ref>
    <description>DB Connection</description>
    <res-ref-name>jdbc/TestDB</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
  </resource-ref>
</web-app>

My Context.xml如下所示：

<?xml version="1.0" encoding="UTF-8"?>
<!--
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
--><!-- The contents of this file will be loaded for each web application --><Context>

    <!-- Default set of monitored resources. If one of these changes, the    -->
    <!-- web application will be reloaded.                                   -->
    <WatchedResource>WEB-INF/web.xml</WatchedResource>
    <WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>

    <!-- Uncomment this to disable session persistence across Tomcat restarts -->
    <!--
    <Manager pathname="" />
    -->

    <!-- Uncomment this to enable Comet connection tacking (provides events
         on session expiration as well as webapp lifecycle) -->
    <!--
    <Valve className="org.apache.catalina.valves.CometConnectionManagerValve" />
    -->

    <Resource name="jdbc/TestDB" auth="Container" type="javax.sql.DataSource"
               maxTotal="100" maxIdle="30" maxWaitMillis="10000"
               username="javauser" password="javadude" driverClassName="com.mysql.jdbc.Driver"
               url="jdbc:mysql://localhost:3306/javatest"/>

</Context>

我的servlet看起来像：

package demo;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.SQLException;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletConfig;
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.sql.DataSource;

/**
 * Servlet implementation class DatasourceDemo
 */
@WebServlet("/DatasourceDemo")
public class DatasourceDemo extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private DataSource ds;   
    /**
     * @see HttpServlet#HttpServlet()
     */
    public DatasourceDemo() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Servlet#init(ServletConfig)
     */
    public void init(ServletConfig config) throws ServletException {
        try {
            InitialContext initContext = new InitialContext();

            Context env = (Context)initContext.lookup("java:com/env");

            ds = (DataSource) env.lookup("jdbc/TestDB");

        } catch (NamingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();

        Connection conn = null;

        try {
            conn = ds.getConnection();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            //e.printStackTrace();
            out.println("Connection error");
            return;
        }

        out.println("Finally connected");

        /*try {
            conn.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }*/
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}

我正在使用Eclipse Luna。 有人可以帮我吗？ 任何帮助深表感谢 感谢