——运行项目时遇到 java.lang.ClassNotFoundException: com.mysql.jdbc.Driver 问题，解决方案:
错误如下：
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1358)
at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1180)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:259)
at com.niuyun.dao.BaseDao.getConnection(BaseDao.java:44)
at com.niuyun.service.user.UserServiceImpl.login(UserServiceImpl.java:26)
at com.niuyun.servlet.user.UserServlet.doGet(UserServlet.java:31)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:626)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
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:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at com.niuyun.filter.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:18)
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:543)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:690)
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:615)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:818)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1626)
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)
解决方案如下：
1.首先检查了一下连接数据库的配置信息是否写错？
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306~~~
username=
password=
莫有啊，写的没有毛病~
2.检查了一下pom.xml配置中是否没有导入相对应的依赖？
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.49</version>
</dependency>
莫有啊，导入依赖了~
也有了呀，但是错误依旧~
3.查看Maven仓库中是否有没下载的包？发现也有啊！（以下是我本地的仓库）
4.查看Tomcat中的lib目录下是否有相对应的jar包，发现确实没有（服务器运行所需要的jar包）。
解决：将连接数据库的包导入，可直接复制你的仓库目录中的jar包，将它放置在lib目录下，即可！
5.问题终于找到了，解决后；重新启动服务器，运行项目，成功了；
（有时候导入包，它可能导不进来，需要手动导入一下）。
希望可以帮助到您，解决问题