postMan上调用合同服务，后台运行错误，如下：
{ "timestamp": 1536203887641, "status": 500, "error": "Internal Server Error", "exception": "org.mybatis.spring.MyBatisSystemException", "message": "nested exception is org.apache.ibatis.exceptions.PersistenceException: \n### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Communications link failure\n\nThe last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.)\n### The error may exist in file [/Users/lizhao/Documents/code/retail-seal/seal-server/target/classes/mappers/ContractTemplateDetailMapper.xml]\n### The error may involve tech.fullink.stone.seal.server.dao.mappers.ContractTemplateDetailMapper.selectByContractCode\n### The error occurred while executing a query\n### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Communications link failure\n\nThe last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.)", "path": "/retail-seal/api/v1/seal" }
网上针对“jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection”关键字搜索一番之后，发现并不匹配目前的情况。仔细检查了下数据库连接的各种配置，发现准确无误。
实在无解的情况下，针对查询语句写单元测试，发现了不同的错误提示：
### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: 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.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:150) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77) 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 org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433) ... 40 more Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Communications link failure The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.) at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80) at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:82) at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:68) at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:338) at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:84) at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62) at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:326) at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49) at com.github.pagehelper.SqlUtil._processPage(SqlUtil.java:401) at com.github.pagehelper.SqlUtil.processPage(SqlUtil.java:374) at com.github.pagehelper.PageHelper.intercept(PageHelper.java:254) at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:61) at com.sun.proxy.$Proxy140.query(Unknown Source) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148) ... 47 more Caused by: org.apache.commons.dbcp.SQLNestedException: 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.dbcp.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:1549) at org.apache.commons.dbcp.BasicDataSource.createDataSource(BasicDataSource.java:1388) at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044) at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111) at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77) ... 67 more Caused by: 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: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:408) at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1137) at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:356) at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2504) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2541) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2323) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:832) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46) 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:408) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:417) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:344) at org.apache.commons.dbcp.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:38) at org.apache.commons.dbcp.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:582) at org.apache.commons.dbcp.BasicDataSource.validateConnectionFactory(BasicDataSource.java:1556) at org.apache.commons.dbcp.BasicDataSource.createPoolableConnectionFactory(BasicDataSource.java:1545) ... 71 more Caused by: java.net.UnknownHostException: saas.database: nodename nor servname provided, or not known at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method) at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:928) at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1323) at java.net.InetAddress.getAllByName0(InetAddress.java:1276) at java.net.InetAddress.getAllByName(InetAddress.java:1192) at java.net.InetAddress.getAllByName(InetAddress.java:1126) at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:250) at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:306) ... 87 more
看到提示瞬间明白，因为本服务是其他服务改造的，本地配置没有起作用，删掉云配置ok。
总结：单元测试很重要。现有服务改造的服务注意云配置。
