java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

在使用Jsp+servlet+JavaBean模式实现一个简单登录功能的时候碰见上述错误！

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
	at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1275)
	at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1104)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at com.jerome.db.DbManager.getConnection(DbManager.java:36)
	at com.jerome.db.DbManager.queryMethod(DbManager.java:64)
	at com.jerome.Dao.UserDao.checkUser(UserDao.java:23)
	at com.jerome.service.UserServiceImpl.checkUserService(UserServiceImpl.java:16)
	at com.jerome.servlet.LoginServlet.doPost(LoginServlet.java:55)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:494)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:651)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:407)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:754)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1376)
	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:748)

然后各种调试，发现数据库压根就没有连接上，然后疯狂纳闷，同样使用JDBC，以前连接压根就没有失败过。

本以为是maven的mysql的Jar包问题，然后各种排查，发现压根没有问题。

数据库连接驱动，数据库登陆user,password,需要连接的库名，表名，sql语句等等都没有问题！

那问题出在哪？

检查tomcat！
找到tomcat的配置–>Deployment


原因是没有将所有的Jar包导入到tomcat的lib目录下

Put into Output Root

然后项目完美运行！