为什么我为Class.forName("com.mysql.jdbc.Driver")获取类找不到异常;

Question

我正在开发一个Web应用程序使用:eclipse IDE(Marse),Java 8,Apache tomcat 8,MySQL.我的用户注册代码如下:

System.out.println("Connecting....");
            Class.forName("com.mysql.jdbc.Driver");
            System.out.println("Class found....");
            String url="jdbc:mysql://localhost:3306/db";
            String user="root";
            String password="root";
            System.out.println("success");
            Connection conn = DriverManager.getConnection(url,user,password);
            String query = "insert into login (username,password,emailid,country,city) values (?,?,?,?,?)";
            PreparedStatement ps = conn.prepareStatement(query);
            ps.setString(1,b.getUsername());
            ps.setString(2,b.getPassword());
            ps.setString(3,b.getEmailid());
            ps.setString(4,b.getCountry());
            ps.setString(5,b.getCity());
            int count=ps.executeUpdate();
            ps.close();
            conn.close();

我的代码也是正确的,我在eclipse中使用Build path> add_external_jar选项添加了mysql-connector-java-5.1.36.但仍然为什么它给我这样的例外呢？

连接....抛出java.lang.ClassNotFoundException:com.mysql.jdbc.Driver在org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1332)在org.apache.catalina.loader.WebappClassLoaderBase.loadClass(位于控制器的model.InfoModel.SaveInfo(InfoModel.java:14)的java.lang.Class.forName(未知来源)的java.lang.Class.forName0(本地方法)中的WebappClassLoaderBase.java:1166)(Reg.Register_user.doGet) Register_user.java:35)在javax.servlet.http.HttpServlet.service(HttpServlet.java:622)在javax.servlet.http.HttpServlet.service(HttpServlet.java:729)在org.apache.catalina.core.ApplicationFilterChain .internalDoFilter(ApplicationFilterChain.java:291)位于org.apache的org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206).tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)在org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)在org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.的java:206)在org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)在org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)在org.apache.catalina.authenticator .AuthenticatorBase.invoke(AuthenticatorBase.java:502)在org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)在org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)在在org.apache.catalina.core上的org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616).StandardEngineValve.invoke(StandardEngineValve.java:88)在org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)在org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)在组织位于org.apache.tomcat.util.net的org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1526)的.apache.coyote.AbstractProtocol $ AbstractConnectionHandler.process(AbstractProtocol.java:673) .NioEndpoint $ SocketProcessor.run(NioEndpoint.java:1482)位于org.apache.tomcat的java.util.concurrent.ThreadPoolExecutor $ Worker.run(未知来源)的java.util.concurrent.ThreadPoolExecutor.runWorker(未知来源). util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Unknown Source)java:88)org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)at org.apache.coyote.AbstractProtocol org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1526)位于org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.run的$ AbstractConnectionHandler.process(AbstractProtocol.java:673) (NioEndpoint.java:1482)java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)at java.util.concurrent.ThreadPoolExecutor $ Worker.run(Unknown Source)at org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Unknown Source)java:88)org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)at org.apache.coyote.AbstractProtocol org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1526)位于org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.run的$ AbstractConnectionHandler.process(AbstractProtocol.java:673) (NioEndpoint.java:1482)java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)at java.util.concurrent.ThreadPoolExecutor $ Worker.run(Unknown Source)at org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(Unknown Source)java:518)org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)atg.apache.coyote.AbstractProtocol $ AbstractConnectionHandler.process(AbstractProtocol.java:673)org.apache.tomcat.util .net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1526)atg.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.run(NioEndpoint.java:1482)at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown来自java.util.concurrent.ThreadPoolExecutor $ Worker.run(未知来源)at org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(未知来源)java:518)org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)atg.apache.coyote.AbstractProtocol $ AbstractConnectionHandler.process(AbstractProtocol.java:673)org.apache.tomcat.util .net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1526)atg.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.run(NioEndpoint.java:1482)at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown来自java.util.concurrent.ThreadPoolExecutor $ Worker.run(未知来源)at org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61)at java.lang.Thread.run(未知来源)在Org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1526)的org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor中的AbstractProtocol $ AbstractConnectionHandler.process(AbstractProtocol.java:673).运行(NioEndpoint.java:1482)java.util.concurrent.ThreadPoolExecutor.runWorker(未知来源)java.util.concurrent.ThreadPoolExecutor $ Worker.run(未知来源)org.apache.tomcat.util.threads.TaskThread java.lang.Thread.run上的$ WrappingRunnable.run(TaskThread.java:61)(未知来源)在Org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor.doRun(NioEndpoint.java:1526)的org.apache.tomcat.util.net.NioEndpoint $ SocketProcessor中的AbstractProtocol $ AbstractConnectionHandler.process(AbstractProtocol.java:673).运行(NioEndpoint.java:1482)java.util.concurrent.ThreadPoolExecutor.runWorker(未知来源)java.util.concurrent.ThreadPoolExecutor $ Worker.run(未知来源)org.apache.tomcat.util.threads.TaskThread java.lang.Thread.run上的$ WrappingRunnable.run(TaskThread.java:61)(未知来源)java.util.concurrent.ThreadPoolExecutor中的runWorker(未知源)$ worker.run(未知源)位于java.lang.Thread的org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61) .run(未知来源)java.util.concurrent.ThreadPoolExecutor中的runWorker(未知源)$ worker.run(未知源)位于java.lang.Thread的org.apache.tomcat.util.threads.TaskThread $ WrappingRunnable.run(TaskThread.java:61) .run(未知来源)

Answer 1

右键单击项目,转到Properties.Deployment Assembly从左窗格中选择(如果未找到,请阅读更新部分).检查是否Java Build Path Entries提供.如果没有,请单击Add并包含它.如果已经存在,请单击Add以将连接器jar包括为Archive.执行Project> Clean,重新启动服务器.

更新

如果项目没有多面,您将找不到此选项.您可以单击Project Facets,转换为分面结构并添加Dynamic Web Module相关的依赖项.

更新

Web部署程序集问题.在大多数情况下,这个答案很有用.