使用netbeans无法连接mysql 7.4

Question

我想运行一个使用mysql的web应用程序。但每次运行应用程序时，我都会收到错误“通信链接失败”。

和堆栈跟踪是：

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. 
SEVERE: com.mysql.jdbc.exceptions.jdbc4.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 sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) 
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526) 
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) 
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116) 
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:344) 
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2332) 
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2369) 
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2153) 
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:792) 
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) 
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) 
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) 
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) 
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526) 
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) 
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:381) 
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:305) 
    at java.sql.DriverManager.getConnection(DriverManager.java:571) 
    at java.sql.DriverManager.getConnection(DriverManager.java:215) 
    at servlets.login.doPost(login.java:76) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) 
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160) 
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734) 
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673) 
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174) 
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:357) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260) 
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188) 
    at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191) 
    at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168) 
    at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189) 
    at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114) 
    at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77) 
    at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838) 
    at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113) 
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115) 
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55) 
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135) 
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564) 
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) 
    at java.lang.Thread.run(Thread.java:744) 
Caused by: java.net.ConnectException: Connection refused 
    at java.net.PlainSocketImpl.socketConnect(Native Method) 
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339) 
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200) 
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182) 
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392) 
    at java.net.Socket.connect(Socket.java:579) 
    at java.net.Socket.connect(Socket.java:528) 
    at java.net.Socket.<init>(Socket.java:425) 
    at java.net.Socket.<init>(Socket.java:241) 
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:257) 
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:294) 
    ... 44 more 

我使用jdk.1.7更新51，并用它作为默认的java。 请建议我在做什么错

Answer 1

所以，你有一个

CommunicationsException：通信链路故障

我从this answer其中也包含了一步一步的MySQL + JDBC教程引用：

如果你得到的SQLException：连接被拒绝或连接超时或MySQL的具体CommunicationsException：

通信链路故障，那么它的意思s数据库根本无法访问。这可能有以下原因之一或多个：

1. IP address or hostname in JDBC URL is wrong. 

2. Hostname in JDBC URL is not recognized by local DNS server. 

3. Port number is missing or wrong in JDBC URL. 

4. DB server is down. 

5. DB server doesn't accept TCP/IP connections. 

6. DB server has run out of connections. 

7. Something in between Java and DB is blocking connections, e.g. a 
    firewall or proxy. 

为了解决一个或另一个，遵循以下建议：

1. Verify and test them with ping. 

2. Refresh DNS or use IP address in JDBC URL instead. 

3. Verify it based on my.cnf of MySQL DB. 

4. Start the DB. 

5. Verify if mysqld is started without the --skip-networking option. 

6. Restart the DB and fix your code accordingly that it closes 
    connections in finally. 

7. Disable firewall and/or configure firewall/proxy to allow/forward 
    the port.