jdbc报错 :com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

报错详细：

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.jdbc.Util.handleNewInstance(Util.java:425)    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990)    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2186)    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2219)    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2014)    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:776)    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:386)    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 sqg.designfn.db.DataConnection.<init>(DataConnection.java:22)    at sqg.designfn.dao.proxy.MovieDAOProxy.<init>(MovieDAOProxy.java:24)    at sqg.designfn.factory.MovieFactory.getIMovieDAOInstance(MovieFactory.java:11)    at sqg.designfn.servlet.ShowMovieServlet.doGet(ShowMovieServlet.java:30)    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)    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:475)    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)    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:342)    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:500)    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: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)Caused by: java.net.ConnectException: Connection refused: connect    at java.net.DualStackPlainSocketImpl.connect0(Native Method)    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)    at java.net.Socket.connect(Socket.java:589)    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300)    ... 42 morecom.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failureThe 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.jdbc.Util.handleNewInstance(Util.java:425)    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:990)    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2186)    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2219)    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2014)    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:776)    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:386)    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 sqg.designfn.db.DataConnection.<init>(DataConnection.java:22)    at sqg.designfn.dao.proxy.MovieDAOProxy.<init>(MovieDAOProxy.java:24)    at sqg.designfn.factory.MovieFactory.getIMovieDAOInstance(MovieFactory.java:11)    at sqg.designfn.servlet.ShowMovieServlet.doGet(ShowMovieServlet.java:30)    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)    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:475)    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)    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:342)    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:500)    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: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)Caused by: java.net.ConnectException: Connection refused: connect    at java.net.DualStackPlainSocketImpl.connect0(Native Method)    at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)    at java.net.Socket.connect(Socket.java:589)    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300)    ... 42 more

原因：MySQL服务没启。

解决：选中“计算机”，右键“管理”，选中“服务和应用程序”，“服务”，找到MySQL服务，启动。可以设置MySQL服务为自动启动，避免每次启动的麻烦（操作附图2张）。

图一 启动MySQL服务

图二 设置为自启动