java.lang.NoClassDefFoundError：mysql数据库连接驱动

我试图运行简单的代码与mysql连接。我正在使用eclipse和tomcat。我在库中添加了mysql-connector-java-8.0.1.9.jar：

库-> mysql-> mysql-connector-java-8.0.1.9.jar

我已经花了几个小时来添加和删除mysql-connector-java-8.0.1.9.jar来构建路径，但它无法运行。请帮忙。我需要在运行配置中添加任何东西吗？

这是Eclipse浏览器上的错误：

HTTP Status 500 – Internal Server Error


Type Exception Report

Message javax.servlet.ServletException: java.lang.NoClassDefFoundError: com/mysql/jdbc/Driver

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception 
org.apache.jasper.JasperException: javax.servlet.ServletException: java.lang.NoClassDefFoundError: com/mysql/jdbc/Driver
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:599)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:500)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)



Root Cause 
javax.servlet.ServletException: java.lang.NoClassDefFoundError: com/mysql/jdbc/Driver
    org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:917)
    org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:846)
    org.apache.jsp.regCheck_jsp._jspService(regCheck_jsp.java:129)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:71)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)



Root Cause 
java.lang.NoClassDefFoundError: com/mysql/jdbc/Driver
    compute.DB.con(DB.java:21)
    org.apache.jsp.regCheck_jsp._jspService(regCheck_jsp.java:100)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:71)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)



Root Cause 
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1951)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1794)
    compute.DB.con(DB.java:21)
    org.apache.jsp.regCheck_jsp._jspService(regCheck_jsp.java:100)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:71)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)



Note The full stack trace of the root cause is available in the server logs.

这是控制台中的输出：

> Mar 16, 2020 4:57:27 PM org.apache.catalina.core.StandardContext reload
INFO: Reloading Context with name [/Mysql] has started
Mar 16, 2020 4:57:27 PM org.apache.catalina.core.StandardContext reload
INFO: Reloading Context with name [/Mysql] is completed
Mar 16, 2020 4:57:41 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [/Mysql] threw exception [javax.servlet.ServletException: java.lang.NoClassDefFoundError: com/mysql/jdbc/Driver] with root cause
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1951)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1794)
    at compute.DB.con(DB.java:21)
    at org.apache.jsp.regCheck_jsp._jspService(regCheck_jsp.java:100)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:71)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:477)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:492)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:165)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:1025)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:452)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1195)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:654)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:319)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.base/java.lang.Thread.run(Thread.java:834)

Try - 05 Trying to establish con in regCheck.jsp
Con method called Try 5A
Try 05a - Trying to connect

这是DB.java：

package compute;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
import java.sql.*;

public class DB {


    final static String DB_URL = "jdbc:mysql://localhost:3306/new";
    final static String USER = "admin";
    final static String PASS = "admin";

    public static Connection con() {
        System.out.println("Con method called Try 5A");
        Connection con;
        try {
            System.out.println("Try 05a - Trying to connect");
            DriverManager.registerDriver(new com.mysql.jdbc.Driver());
            con = DriverManager.getConnection(DB_URL, USER, PASS);
            System.out.println("Try 05a- con established ");
            return con;
        }catch(Exception e) {
            System.out.println(e);
            return null;
        }
    }

    public static Statement st() {
        Statement stmt;
        try {
            stmt=DB.con().createStatement();
            return null;
        }catch(Exception e) {
            System.out.println(e);
            return null;
        }
    }
}

这是regCheck.jsp：

<%@page import="java.sql.Connection" %>
<%@page import="compute.DB" %>
<%@page import="java.sql.PreparedStatement" %>

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="ISO-8859-1">
        <title>Insert title here</title>
    </head>
    <body>
        <%
        String user = request.getParameter("username");
        System.out.println("Try - 05 Trying to establish con in regCheck.jsp");
        Connection con = DB.con();
        System.out.println("Preparing Statement in regCheck.jsp");
        PreparedStatement p = con.prepareStatement("Insert into register(username)values(?)");

        p.setString(1,user);
        System.out.println("user::" +user);

        int R = p.executeUpdate();
        if(R!=0)
            response.sendRedirect("index.html");
        else
            response.sendRedirect("register.jsp");

        %>

    </body>
</html>

问题来源：Stack Overflow

1，检查下跑是否成功被ref，如果是POM配置看下依赖中是否引入正确。参考：在mysql的官网可以得到想要的版本。

选择要引入驱动的项目右键->建立路径->配置路径在打开的包含的四个选项卡的窗口中选择库这个选项卡选择添加外部JAR包->ok 在你驱动JAR包存放的地方选择好你的JAR包->打开测试连接代码：

public class Dao {

// 公用的数据库连接类

public static Connection getConnection() throws Exception {

String driverName = "com.mysql.jdbc.Driver"; // 加载JDBC驱动

String dbURL = "jdbc:mysql://localhost:3306/test_scheme?auotReconnect=true&useUnicode=true&characterEncoding=utf8"; // 连接服务器和数据login

// System.out.print(dbURL);

String userName = "root"; // 用户名

String userPwd = ""; // 密码

Class.forName(driverName);

return DriverManager.getConnection(dbURL, userName, userPwd);

}

public static void main(String []s){

try {

String sql="select * from test_table";

PreparedStatement psmt=getConnection().prepareStatement(sql);

ResultSet rs=psmt.executeQuery();

while(rs.next()){

System.out.println(rs.getString(1));

}

} catch (Exception e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

java.lang.NoClassDefFoundError：mysql数据库连接驱动

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