日志里打印：
10:39:48.962 [Druid-ConnectionPool-Create-1315749361] [] [] ERROR c.alibaba.druid.pool.DruidDataSource - create connection error com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection, message from server: "Too many connections" 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:409) at com.mysql.jdbc.Util.getInstance(Util.java:384) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1013) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:987) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:973) at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1112) at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2506) at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2539) at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2321) at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:832) at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46) at sun.reflect.GeneratedConstructorAccessor31.newInstance(Unknown Source) 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:409) at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:417) at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:344) at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1368) at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1424) at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:1680)
看mysql数据库实际的连接数：
mysql> show variables like ‘%max_connections%‘; +-----------------+-------+ | Variable_name | Value | +-----------------+-------+ | max_connections | 700 | +-----------------+-------+ 1 row in set (0.01 sec)
想看具体都有哪些连接，执行：
mysql> show full processlist;
改连接数，重启失效：
mysql> set GLOBAL max_connections=1000; Query OK, 0 rows affected (0.00 sec) mysql> show variables like ‘%max_connections%‘; +-----------------+-------+ | Variable_name | Value | +-----------------+-------+ | max_connections | 1000 | +-----------------+-------+ 1 row in set (0.01 sec)
真要永久修改，得去my.cnf配置文件里改max_connections属性。