Java 为什么我找不到 Class.forName("com.mysql.jdbc.Driver") 的异常类；

Why I am getting class not found exception for Class.forName("com.mysql.jdbc.Driver");

提问by Abhijit Kumbhar

I am developing an web app Using : eclipse IDE(Marse), Java 8, Apache tomcat 8, MySQL. My code for user registration is as follows:

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();

My code is also correct and also I added mysql-connector-java-5.1.36by using Build path>add_external_jaroption in eclipse. But still why it gives me such a exception ?

我的代码也是正确的，我还通过在 eclipse 中使用Build path>add_external_jar选项添加了 mysql-connector-java-5.1.36。但是为什么它给了我这样的例外？

Connecting.... java.lang.ClassNotFoundException: com.mysql.jdbc.Driver at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1332) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1166) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Unknown Source) at model.InfoModel.SaveInfo(InfoModel.java:14) at controller.Register_user.doGet(Register_user.java:35) at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1482) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)

正在连接.... java.lang.ClassNotFoundException: com.mysql.jdbc.Driver at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1332) at org.apache.catalina.loader.WebappClassLoaderBase.loadClass( WebappClassLoaderBase.java:1166) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Unknown Source) at model.InfoModel.SaveInfo(InfoModel.java:14) at controller.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) 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) 在 org.apache。tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain. java:206) 在 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) 在 org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) 在 org.apachetic.catalina.authen .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) org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616) 在 org.apache.catalina.core。StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) at .apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) 在 org.apache.tomcat.util.net .NioEndpoint$SocketProcessor.run(NioEndpoint.java:1482) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat。 util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) 在 java.lang.Thread.run（未知来源）java:88) 在 org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518) 在 org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) 在 org.apache.coyote.AbstractProtocol $AbstractConnectionHandler.process(AbstractProtocol.java:673) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run (NioEndpoint.java:1482) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$ WrappingRunnable.run(TaskThread.java:61) 在 java.lang.Thread.run（未知来源）java:88) 在 org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518) 在 org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) 在 org.apache.coyote.AbstractProtocol $AbstractConnectionHandler.process(AbstractProtocol.java:673) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run (NioEndpoint.java:1482) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$ WrappingRunnable.run(TaskThread.java:61) 在 java.lang.Thread.run（未知来源）java:518) 在 org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) 在 org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673) 在 org.apache.tomcat.util .net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1482) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(来源不明）java:518) 在 org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) 在 org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673) 在 org.apache.tomcat.util .net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1482) 在 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(来源不明）AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor。 run(NioEndpoint.java:1482) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread $WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:673) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1526) 在 org.apache.tomcat.util.net.NioEndpoint$SocketProcessor。 run(NioEndpoint.java:1482) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread $WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread .run（未知来源）runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread .run（未知来源）

采纳答案by James Jithin

Right click on the Project, go to Properties. Choose Deployment Assembly(if not found, read the update part) from the left pane. Check if Java Build Path Entriesare provided. If not, click on Addand include it. If it is already present, click Addto include your connector jar as Archive. Do a Project>Clean, restart your Server.

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。如果它已经存在，请单击Add以将您的连接器 jar 包含为Archive. 做一个Project> Clean，重新启动你的服务器。

Update

更新

If the Project is not being Faceted, you will not find this option. You can click on Project Facets, convert to faceted structure and add Dynamic Web Moduleand related dependencies.

如果项目没有被分面，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和相关的依赖项。

Update

更新

Web Deployment Assembly Problem. This answer is helpful in most cases.

Web 部署程序集问题。这个答案在大多数情况下是有帮助的。