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

代码明明正确，数据库信息 等配置都正确，但偏偏抛如下异常

2017-04-22 15:12:04.772 ERROR 13496 --- [           main] o.a.tomcat.jdbc.pool.ConnectionPool      : Unable to create initial connections of pool.com.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) ~[na:1.8.0_31]at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at java.lang.reflect.Constructor.newInstance(Unknown Source) ~[na:1.8.0_31]at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1117) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:350) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2393) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2430) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2215) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:813) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) ~[mysql-connector-java-5.1.21.jar:na]at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_31]at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at java.lang.reflect.Constructor.newInstance(Unknown Source) ~[na:1.8.0_31]at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:399) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:334) ~[mysql-connector-java-5.1.21.jar:na]at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:307) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:200) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:708) [tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:642) [tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:464) [tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:141) [tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:115) [tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:102) [tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.DataSourceProxy.getConnection(DataSourceProxy.java:126) [tomcat-jdbc-8.0.30.jar:na]at org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:204) [spring-jdbc-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:373) [spring-tx-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.transaction.TransactionContext.startTransaction(TransactionContext.java:98) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.transaction.TransactionalTestExecutionListener.beforeTestMethod(TransactionalTestExecutionListener.java:194) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.TestContextManager.beforeTestMethod(TestContextManager.java:265) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) [junit-4.12.jar:4.12]at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:254) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) [junit-4.12.jar:4.12]at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.junit.runners.ParentRunner.run(ParentRunner.java:363) [junit-4.12.jar:4.12]at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:193) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) [.cp/:na]Caused by: java.net.ConnectException: Connection timed out: connectat java.net.DualStackPlainSocketImpl.connect0(Native Method) ~[na:1.8.0_31]at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source) ~[na:1.8.0_31]at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source) ~[na:1.8.0_31]at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source) ~[na:1.8.0_31]at java.net.AbstractPlainSocketImpl.connect(Unknown Source) ~[na:1.8.0_31]at java.net.PlainSocketImpl.connect(Unknown Source) ~[na:1.8.0_31]at java.net.SocksSocketImpl.connect(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.connect(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.connect(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.<init>(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.<init>(Unknown Source) ~[na:1.8.0_31]at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:257) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300) ~[mysql-connector-java-5.1.21.jar:na]... 47 common frames omitted2017-04-22 15:12:04.774  WARN 13496 --- [           main] o.s.test.context.TestContextManager      : Caught exception while allowing TestExecutionListener [org.springframework.test.context.transaction.TransactionalTestExecutionListener@52a86356] to process 'before' execution of test method [public void com.didispace.ApplicationTests.findByName() throws java.lang.Exception] for test instance [com.didispace.ApplicationTests@5bc79255]org.springframework.transaction.CannotCreateTransactionException: Could not open JDBC Connection for transaction; nested exception is com.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 org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:245) ~[spring-jdbc-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:373) ~[spring-tx-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.transaction.TransactionContext.startTransaction(TransactionContext.java:98) ~[spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.transaction.TransactionalTestExecutionListener.beforeTestMethod(TransactionalTestExecutionListener.java:194) ~[spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.TestContextManager.beforeTestMethod(TestContextManager.java:265) ~[spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) [junit-4.12.jar:4.12]at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:254) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) [junit-4.12.jar:4.12]at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) [junit-4.12.jar:4.12]at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.junit.runners.ParentRunner.run(ParentRunner.java:363) [junit-4.12.jar:4.12]at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:193) [spring-test-4.2.4.RELEASE.jar:4.2.4.RELEASE]at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382) [.cp/:na]at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192) [.cp/:na]Caused by: com.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) ~[na:1.8.0_31]at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at java.lang.reflect.Constructor.newInstance(Unknown Source) ~[na:1.8.0_31]at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1117) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:350) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2393) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2430) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2215) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:813) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) ~[mysql-connector-java-5.1.21.jar:na]at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_31]at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) ~[na:1.8.0_31]at java.lang.reflect.Constructor.newInstance(Unknown Source) ~[na:1.8.0_31]at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:399) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:334) ~[mysql-connector-java-5.1.21.jar:na]at org.apache.tomcat.jdbc.pool.PooledConnection.connectUsingDriver(PooledConnection.java:307) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.PooledConnection.connect(PooledConnection.java:200) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.createConnection(ConnectionPool.java:708) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:642) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.init(ConnectionPool.java:464) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.ConnectionPool.<init>(ConnectionPool.java:141) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.DataSourceProxy.pCreatePool(DataSourceProxy.java:115) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.DataSourceProxy.createPool(DataSourceProxy.java:102) ~[tomcat-jdbc-8.0.30.jar:na]at org.apache.tomcat.jdbc.pool.DataSourceProxy.getConnection(DataSourceProxy.java:126) ~[tomcat-jdbc-8.0.30.jar:na]at org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:204) ~[spring-jdbc-4.2.4.RELEASE.jar:4.2.4.RELEASE]... 25 common frames omittedCaused by: java.net.ConnectException: Connection timed out: connectat java.net.DualStackPlainSocketImpl.connect0(Native Method) ~[na:1.8.0_31]at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source) ~[na:1.8.0_31]at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source) ~[na:1.8.0_31]at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source) ~[na:1.8.0_31]at java.net.AbstractPlainSocketImpl.connect(Unknown Source) ~[na:1.8.0_31]at java.net.PlainSocketImpl.connect(Unknown Source) ~[na:1.8.0_31]at java.net.SocksSocketImpl.connect(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.connect(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.connect(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.<init>(Unknown Source) ~[na:1.8.0_31]at java.net.Socket.<init>(Unknown Source) ~[na:1.8.0_31]at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:257) ~[mysql-connector-java-5.1.21.jar:na]at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300) ~[mysql-connector-java-5.1.21.jar:na]... 47 common frames omitted2017-04-22 15:12:04.794  INFO 13496 --- [       Thread-1] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@1b1473ab: startup date [Sat Apr 22 15:11:41 CST 2017]; root of context hierarchy

解决方法如下：

spring.datasource.url=jdbc:mysql://localhost:3306/david  改成 spring.datasource.url=jdbc:mysql://127.0.0.1:3306/david