Question

我使用Spring，学习servlet和所有webstuff，我试图创建一个简单的servlet来连接到mysql服务器..这是我的代码：

AccesoDB：

package es.prueba.servlet;

import java.io.IOException;
import java.io.PrintWriter;
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.ServletConfig;
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 AccesoDB
 */
public class AccesoDB extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private DataSource ds = null;
    ResultSet rs;
    Context ctx;

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

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

        try {
            ctx = new InitialContext();
            ds = (DataSource) ctx.lookup("java:comp/env/jdbc/AccesoBD");
        } catch ( NamingException e) {
            e.printStackTrace();
        }

    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");

        Connection connection = null;

        synchronized(ds) {
            try{
                connection = ds.getConnection();

                PrintWriter out = response.getWriter();
                String query = null;
                Statement stmt;
                query = "SELECT * FROM test";
                stmt = connection.createStatement();

                rs = stmt.executeQuery(query);
                out.println(rs.toString());

                connection.close();
            }catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }

}

context.xml中：

 <Context path="/AccesoDB" docBase=" AccesoBD "
    debug="5" reloadable="true" crossContext="true">
    <Resource name="jdbc/ AccessoBD " auth="Container"
        type="javax.sql.DataSource" maxActive="100"
        maxIdle="30" maxWait="10000" username="test"
        password="test"
        driverClassName="com.mysql.jdbc.Driver"
        url="jdbc:mysql://localhost:3306/dbaplicacion"/>
</Context>

的web.xml：

    <?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" 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>elTiempo</display-name>
  <servlet>
    <display-name>AjaxExample</display-name>
    <servlet-name>AjaxExample</servlet-name>
    <servlet-class>es.prueba.servlet.AjaxExample</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>AjaxExample</servlet-name>
    <url-pattern>/AjaxExample</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>holaMundo.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>
  <resource-ref>
    <res-ref-name>jdbc/AccesoBD</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
  </resource-ref>
  <servlet>
    <description></description>
    <display-name>AccesoDB</display-name>
    <servlet-name>AccesoDB</servlet-name>
    <servlet-class>es.prueba.servlet.AccesoDB</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>AccesoDB</servlet-name>
    <url-pattern>/AccesoDB</url-pattern>
  </servlet-mapping>
</web-app>

以下是错误的痕迹：

    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 es.prueba.servlet.AccesoDB.doGet(AccesoDB.java:62)
    at es.prueba.servlet.AccesoDB.doPost(AccesoDB.java:83)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:643)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:744)
Caused by: java.lang.NullPointerException
    at sun.jdbc.odbc.JdbcOdbcDriver.getProtocol(JdbcOdbcDriver.java:524)
    at sun.jdbc.odbc.JdbcOdbcDriver.knownURL(JdbcOdbcDriver.java:493)
    at sun.jdbc.odbc.JdbcOdbcDriver.acceptsURL(JdbcOdbcDriver.java:307)
    at java.sql.DriverManager.getDriver(DriverManager.java:262)
    at org.apache.tomcat.dbcp.dbcp.BasicDataSource.createConnectionFactory(BasicDataSource.java:1437)
    ... 18 more

错误在于：

connection = ds.getConnection();

但我无法弄清楚，正如我之前所说，我正在学习而其他线程并没有帮助我。

编辑：启动Tomcat时我也遇到此错误，如果重要则不知道：

java.lang.IllegalArgumentException: El Documento base C:\Program Files\Apache Software Foundation\Tomcat 6.0\webapps\context no existe o no es un directorio legible
    at org.apache.naming.resources.FileDirContext.setDocBase(FileDirContext.java:142)
    at org.apache.catalina.core.StandardContext.resourcesStart(StandardContext.java:4320)
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:4489)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:799)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:779)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:601)
    at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:675)
    at org.apache.catalina.startup.HostConfig.deployDescriptors(HostConfig.java:601)
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:502)
    at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1317)
    at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:324)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:142)
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1065)
    at org.apache.catalina.core.StandardHost.start(StandardHost.java:840)
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057)
    at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:463)
    at org.apache.catalina.core.StandardService.start(StandardService.java:525)
    at org.apache.catalina.core.StandardServer.start(StandardServer.java:754)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:595)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)

Answer 1

解决了..问题是..我正在以这种方式访问数据源：

ds = (DataSource) ctx.lookup("java:comp/env/jdbc/AccesoBD");

并且是：

ds = (DataSource) ctx.lookup("java:comp/env/jdbc/AccesoDB");

我用BD换了DB :)无论如何都是^ ^

Answer 2

将MySQL JDBC驱动程序JAR放在Tomcat server / lib目录中，而不是上下文WEB-INF / lib文件夹中。

资源名称中还有一个额外的空格：

<Resource name="jdbc/ AccessoBD " auth="Container"

删除它，看看是否有帮助。

无法为连接URL“null”和NullPointerException创建类''的JDBC驱动程序

2 个答案: