解决异常：“The last packet sent successfully to the server was 0 milliseconds ago. ”

问题背景：昨天运行正常的项目，今天突然不能运行了，并且提示一下错误：

java.sql.SQLException: Cannot create PoolableConnectionFactory
(Communications link failure

The last packet sent successfully to the server was 0 milliseconds
ago. The driver has not received any packets from the server.) at
org.apache.commons.dbcp2.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:669)
at
org.apache.commons.dbcp2.BasicDataSource.createDataSource(BasicDataSource.java:544)
at
org.apache.commons.dbcp2.BasicDataSource.getConnection(BasicDataSource.java:753)
at util.DBUtil.getConnection(DBUtil.java:39) at
util.DBUtil.getObject(DBUtil.java:102) at
servlet.StudentServlet.getStuInfo(StudentServlet.java:52) at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498) at
servlet.StudentServlet.doGet(StudentServlet.java:29) at
javax.servlet.http.HttpServlet.service(HttpServlet.java:655) at
javax.servlet.http.HttpServlet.service(HttpServlet.java:764) 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 filter.MyFilter.doFilter(MyFilter.java:23) 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:196)
at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
at
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:698)
at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
at
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:364)
at
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:624)
at
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)atorg.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1673)
at
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at
org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
at
org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)atorg.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748) Caused by:
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications
link failure

The last packet sent successfully to the server was 0 milliseconds
ago. The driver has not received any packets from the server. at
com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
at
com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
at
com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:828)
at com.mysql.cj.jdbc.ConnectionImpl.(ConnectionImpl.java:448)
at
com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:241)
at
com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:198)
at
org.apache.commons.dbcp2.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:55)
at
org.apache.commons.dbcp2.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:355)
at
org.apache.commons.dbcp2.BasicDataSource.validateConnectionFactory(BasicDataSource.java:115)
at
org.apache.commons.dbcp2.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:665)
… 37 more Caused by:
com.mysql.cj.exceptions.CJCommunicationsException: Communications link
failure

The last packet sent successfully to the server was 0 milliseconds
ago. The driver has not received any packets from the server. 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.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
at
com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:105)
at
com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:151)
at
com.mysql.cj.exceptions.ExceptionFactory.createCommunicationsException(ExceptionFactory.java:167)
at
com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:89)
at com.mysql.cj.NativeSession.connect(NativeSession.java:120) at
com.mysql.cj.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:948)
at
com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:818)
… 44 more Caused by: java.net.ConnectException: Connection refused:
connect at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at
java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:75)
at
java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:476)
at
java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:218)
at
java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:200)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:162) at
java.net.SocksSocketImpl.connect(SocksSocketImpl.java:394) at
java.net.Socket.connect(Socket.java:606) at
com.mysql.cj.protocol.StandardSocketFactory.connect(StandardSocketFactory.java:156)
at
com.mysql.cj.protocol.a.NativeSocketConnection.connect(NativeSocketConnection.java:63)
… 47 more java.lang.reflect.InvocationTargetException at
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498) at
servlet.StudentServlet.doGet(StudentServlet.java:29) at
javax.servlet.http.HttpServlet.service(HttpServlet.java:655) at
javax.servlet.http.HttpServlet.service(HttpServlet.java:764) 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 filter.MyFilter.doFilter(MyFilter.java:23) 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:196)
at
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
at
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
at
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135)
at
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at
org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:698)
at
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
at
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:364)
at
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:624)
at
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
at
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:831)atorg.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1673)
at
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at
org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
at
org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)atorg.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748) Caused by:
java.lang.NullPointerException at
util.DBUtil.getObject(DBUtil.java:103) at
servlet.StudentServlet.getStuInfo(StudentServlet.java:52) … 32 more

经过几般尝试，发现竟然是Mysql设置的是手动开启，系统默认在关机的时候给它关了。

这里开启就行了。