我在ubuntu系统上的tomcat servlet正常运行并突然崩溃。我重新启动了tomcat，并且servlet无法再连接到mysql。 我还发现登录时mysql不需要密码。 这是servlet的代码：
Class.forName("com.mysql.jdbc.Driver");
Connection conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/larryxu","root","");
我可以在自己的计算机上使用相同的servlet访问mysql，所以我认为问题出在mysql服务器上。 这是catalina.out中的堆栈跟踪：
java.sql.SQLException: Access denied for user 'root'@'localhost'
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:964)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3973)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3909)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:873)
at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1710)
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1226)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2205)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2236)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2035)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:790)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:330)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at larryxu.MainServlet.recordVisitor(MainServlet.java:82)
at larryxu.MainServlet.doPost(MainServlet.java:49)
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:53)
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:199)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:475)
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:498)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:796)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1368)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)