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
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-
个人对建模比较关注排查思路：NoClassDefError主要是因为有class文件，但是classLoader中找不到。这种一般出现在类初始化过程中报错，导致class初始化失败，导致没有加载到classLoader中。所以有更上层的错误原因。可以去看对应class的构造器与父类，以及静态类的过程中是否有其他报错。
2020-03-25 16:38:39赞同 展开评论 打赏 -
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();
}
}
2020-03-22 16:09:58赞同 展开评论 打赏 -
我将mysql-connector-java-8.0.19.jar添加到Tomcat 7.0 / Lib中，现在可以正常工作了。我从图书馆以及所有地方将其删除，并且可以正常工作。我用相同的代码创建了新项目，并且没有将mysql-connector-java-8.0.19.jar添加到任何库或构建路径中，它运行良好。我在YouTube上的某处找到了添加到tomcat的说明。
回答来源：Stack Overflow
2020-03-23 09:43:21赞同 展开评论 打赏
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