java - Tomcat6 和 MySQL 问题

Question

我新安装了带有 Tomcat6 的 Ubuntu 11.10 服务器。我正在使用 Eclipse Indigo 制作一个从我的 MySQL 服务器中提取数据的 Java Servlet。我已将最新的 Connector/J (mysql-connector-java-5.1.18-bin.jar) 放在我的服务器 CATALINA_HOME/lib 目录中。在 Eclipse 中，我创建了一个动态 Web 项目，然后为其创建了一个 servlet。 servlet 的 Java 代码是:

import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

/**
 * Servlet implementation class TestServlet
 */
public class TestServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

/**
 * @see HttpServlet#HttpServlet()
 */
public TestServlet() {
    super();
    // TODO Auto-generated constructor stub
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    Context initCtx = null;
    try {
        initCtx = new InitialContext();
    } catch (NamingException e2) {
        // TODO Auto-generated catch block
        e2.printStackTrace();
    }
    Context envCtx = null;
    try {
        envCtx = (Context) initCtx.lookup("java:comp/env");
    } catch (NamingException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    DataSource ds = null;
    try {
        ds = (DataSource) envCtx.lookup("jdbc/TestDB");
    } catch (NamingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } 
    Connection conn = null;
    try {
        conn = ds.getConnection();
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    Statement stat = null;
    try {
        stat = conn.createStatement();
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    ResultSet rs = null;
    try {
        rs = stat.executeQuery("SELECT * FROM users");
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {
        while(rs.next()) {
            System.out.println("in");
        }
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

}

我的 WEB-INF/web.xml 中有以下内容:

<?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/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>TestServlet</display-name>
  <resource-ref>
    <description>TestDB</description>
    <res-ref-name>jdbc/TestDB</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
  </resource-ref>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <description></description>
    <display-name>TestServlet</display-name>
    <servlet-name>TestServlet</servlet-name>
    <servlet-class>TestServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServlet</servlet-name>
    <url-pattern>/TestServlet</url-pattern>
  </servlet-mapping>
</web-app>

我必须在 META-INF 中创建 context.xml，但这里是我的 META-INF/context.xml 的上下文

<?xml version="1.0" encoding="UTF-8"?>
<Context>
  <Resource name="jdbc/TestDB" auth="Container" type="javax.sql.DataSource"
               maxActive="100" maxIdle="30" maxWait="10000"
               username="myuser" password="mypass" driverClassName="com.mysql.jdbc.Driver"
               url="jdbc:mysql://localhost:3306/test1"/>
</Context>

我导出到一个 war ，部署到我的 tomcat 服务器。当我浏览到 servlet 时，出现以下错误:

java.lang.NullPointerException
TestServlet.doGet(TestServlet.java:67)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

TestServlet.java 的第 67 行是 conn.createStatement();线。抱歉，我的代码很乱，我使用了单独的 try catch block ，因为当我进行一次大的 try catch 时我没有收到此错误，尽管它仍然没有连接到 MySQL 数据库。我确定我在这里错过了一个相当简单的步骤，但我似乎无法在任何地方找到它，我对 Tomcat 和 Servlet 有点陌生。非常感谢。

Answer 1

根据 Tomcat 6 context docs :

Context elements may be explicitly defined:

• Only if a context file does not exist for the application in the $CATALINA_BASE/conf/[enginename]/[hostname]/, in an individual file at /META-INF/context.xml inside the application files. If the web application is packaged as a WAR then /META-INF/context.xml will be copied to $CATALINA_BASE/conf/[enginename]/[hostname]/ and renamed to match the application's context path. Once this file exists, it will not be replaced if a new WAR with a newer /META-INF/context.xml is placed in the host's appBase.

尝试删除 Tomcat 的 conf 目录中的副本，然后查看您的 context.xml 文件是否被拾取。