java - IntelliJ java.lang.ClassNotFoundException : com. mysql.jdbc.Driver - 连接到 XAMPP MySQL 数据库

Question

尝试使用 IntelliJ 在 Java 中创建基本登录页面。我已使用以下说明将 JAR 添加到 CLASSPATH:Adding Jar files to IntellijIdea classpath .我得到的错误如下。

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1285)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1119)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at main.Validate.checkUser(Validate.java:17)
at main.Login.doPost(Login.java:23)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:341)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1441)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
20-Mar-2017 16:14:19.453 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deploying web application directory D:\Users\MYNAME\apache-tomcat-8.5.12\webapps\manager
20-Mar-2017 16:14:19.523 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployDirectory Deployment of web application directory D:\Users\MYNAME\apache-tomcat-8.5.12\webapps\manager has finished in 70 ms

连接到DB的类叫做Validate；

package main;

import java.sql.*;

public class Validate
{
    public static boolean checkUser(String username,String password)
    {

        boolean st =false;
        try{

            //loading drivers for mysql
            Class.forName("com.mysql.jdbc.Driver");

            //creating connection with the database
            Connection con=DriverManager.getConnection
                    ("jdbc:mysql:/ /localhost:3306/wpdcourseworkdb","root","");
            PreparedStatement ps =con.prepareStatement
                    ("select * from users where username=? and password=?");
            ps.setString(1, username);
            ps.setString(2, password);
            ResultSet rs =ps.executeQuery();
            st = rs.next();

        }catch(Exception e)
        {
            e.printStackTrace();
        }
        return st;
    }
}

Answer 1

将库添加到 IntelliJ 的类路径中不会将它们添加到构建工件中，例如.jar 文件。如果您使用 Maven，您应该将依赖项添加到 POM 文件并使用 maven-assembly-plugin 创建一个包含所有需要的依赖项的胖存档:

https://maven.apache.org/plugins/maven-assembly-plugin/usage.html

编辑:在聊天中讨论后发现用户正试图在 tomcat 上部署一个简单的 .jar，而他认为他正在部署一个网络存档。瘦 .jar 不包含所需的依赖项，tomcat 也没有将它们作为其核心的一部分提供。