JNDI 无法在 Tomcat 6 上创建 JDBC 连接

Question

当我尝试查看该页面时，出现此错误：

SQLException: Cannot create JDBC driver of class '' for connect URL 'null'

我有以下 /WEB-INF/web.xml：

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
    <display-name>WSwartzendruber.net</display-name>
    <description>Personal Website</description>
    <!-- Servlet stuff -->
    <servlet>
        <servlet-name>PostgresTest</servlet-name>
        <servlet-class>PostgresTest</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>PostgresTest</servlet-name>
        <url-pattern>/servlets/postgrestest</url-pattern>
    </servlet-mapping>
    <!-- JNDI -->
    <resource-ref>
        <description>PostgreSQL Data Source</description>
        <res-ref-name>jdbc/db_website</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
    </resource-ref>
</web-app>

我在 /META-INF/context.xml 中有此内容：

<?xml version="1.0" encoding="UTF-8"?>
<Context reloadable="true">
    <Resource name="jdbc/db_website" auth="Container" type="javax.sql.DataSource" driverClassName="org.postgresql.Driver" url="jdbc:postgresql://localhost:5432/db_website" username="website"/>
</Context>

这是测试代码：

import java.io.*;
import java.sql.*;
import javax.naming.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.sql.*;
import org.wswartzendruber.website.access.*;

public class PostgresTest extends HttpServlet
{
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException
    {
        response.setContentType("text/plain");

        try
        {
            Context initialContext = new InitialContext();
            Context context = (Context)initialContext.lookup("java:comp/env");
            DataSource dataSource = (DataSource)context.lookup("jdbc/db_website");
            Connection connection = dataSource.getConnection();
            NewsCategory[] newsCategory = NewsCategory.getNewsCategories(connection);

            connection.close();
        }
        catch (NamingException e)
        {
            response.getWriter().println("ERROR: We have naming problems!");
        }
        catch (SQLException se)
        {
            response.getWriter().println("ERROR: SQLException: " + se.getMessage());
        }
        catch (AccessException ae)
        {
            response.getWriter().println("ERROR: AccessException: " + ae.getMessage());
        }
    }
}

我是不知道问题是什么。我已经有 /usr/share/tomcat-6/lib/postgresql-8.4-702.jdbc4.jar 。将其移动到 /WEB-INF/lib 没有什么区别。在我看来，它可以看到 WEB-INF/web.xml 中的资源条目，但无法从 META-INF/context.xml 中提取详细信息。在那里分配密码似乎也没有什么区别。

我愿意接受你们所拥有的一切。

---

更新：这是完整的堆栈跟踪：

Sep 19, 2010 7:01:36 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet PostgresTest threw exception
java.io.IOException: org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null'
    at PostgresTest.doGet(PostgresTest.java:23)
    at javax.servlet.http.HttpServlet.service(Unknown Source)
    at javax.servlet.http.HttpServlet.service(Unknown Source)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Unknown Source)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(Unknown Source)
    at org.apache.catalina.core.StandardWrapperValve.invoke(Unknown Source)
    at org.apache.catalina.core.StandardContextValve.invoke(Unknown Source)
    at org.apache.catalina.core.StandardHostValve.invoke(Unknown Source)
    at org.apache.catalina.valves.ErrorReportValve.invoke(Unknown Source)
    at org.apache.catalina.core.StandardEngineValve.invoke(Unknown Source)
    at org.apache.catalina.connector.CoyoteAdapter.service(Unknown Source)
    at org.apache.jk.server.JkCoyoteHandler.invoke(Unknown Source)
    at org.apache.jk.common.HandlerRequest.invoke(Unknown Source)
    at org.apache.jk.common.ChannelSocket.invoke(Unknown Source)
    at org.apache.jk.common.ChannelSocket.processConnection(Unknown Source)
    at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(Unknown Source)
    at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:636)
Caused by: org.apache.tomcat.dbcp.dbcp.SQLNestedException: Cannot create JDBC driver of class '' for connect URL 'null'
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1452)
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1371)
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
    at PostgresTest.doGet(PostgresTest.java:17)
    ... 17 more
Caused by: java.lang.NullPointerException
    at org.postgresql.Driver.parseURL(Driver.java:567)
    at org.postgresql.Driver.acceptsURL(Driver.java:412)
    at java.sql.DriverManager.getDriver(DriverManager.java:268)
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1437)
    ... 20 more

Answer 1

异常的“由”/“根本原因”部分包含有关其失败原因的信息。您不应仅打印异常消息而忽略异常详细信息的剩余部分。您应该抛出整个异常或至少打印整个堆栈跟踪。

快速修复：将 try 替换为

try {
    Context initialContext = new InitialContext();
    Context context = (Context)initialContext.lookup("java:comp/env");
    DataSource dataSource = (DataSource)context.lookup("jdbc/db_website");
    Connection connection = dataSource.getConnection();
    NewsCategory[] newsCategory = NewsCategory.getNewsCategories(connection);
    connection.close();
} catch (Exception e) {
    throw new ServletException(e);
}

And retry。整个堆栈跟踪应该显示在服务器的默认错误页面中。或者，如果您自定义了错误页面，使其不显示跟踪，那么查看服务器日志，它也在那里。

---

根据评论更新：您只需将 ServletException 添加到 throws 子句即可。根据堆栈跟踪，context.xml 中的资源已正确定位，驱动程序已正确加载，但 URL 尚未传入，就好像未在 中指定一样;。

您确定正在提供您认为正在提供的吗？您在 Tomcat/conf/context.xml 中是否有另一个具有相同名称但没有 url 的 ？

Answer 2

是的，我也遇到了这个问题。如果我将段放入 tomcat/conf/context.xml 中，它就可以工作。我不知道为什么

Answer 3

在 WebRoot/META-INF 文件夹中添加 context.xml 并放入

<!-- Default set of monitored resources -->
<WatchedResource>WEB-INF/web.xml</WatchedResource>
<Resource name="jdbc/ecms" auth="Container" type="javax.sql.DataSource"
    maxActive="100" maxIdle="30" maxWait="10000"
    username="root" password="root123#" driverClassName="com.mysql.jdbc.Driver"
    url="jdbc:mysql://localhost:3306/ecms"/>

在 web.xml 页面中编写

<resource-ref>
        <description>DB Connection</description>
        <res-ref-name>jdbc/ecms</res-ref-name>
        <res-type>javax.sql.DataSource</res-type>
        <res-auth>Container</res-auth>
    </resource-ref>

形成一个新的 java 类并编写

package com.common;

import java.sql.Connection;
import java.sql.SQLException;

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

public class DataSourceq {

    public Connection dbc() throws NamingException, SQLException, ServletException{
        try {
            InitialContext initialContext = new InitialContext();
            Context context = (Context)initialContext.lookup("java:comp/env");
            //The JDBC Data source that we just created
            DataSource ds = (DataSource) context.lookup("jdbc/ecms");
            Connection connection = ds.getConnection();
            return connection;
        }

        catch (Exception e) {
            throw new ServletException(e);
        }
    }
}

为您的数据源类创建对象并调用

DataSourceq dq = new DataSourceq();
Connection con =  dq.dbc(); 

并执行您的查询它将成功工作