java.sql.SQLException: Unknown system variable 'tx_isolation'

MySQL数据库连接的时报错：

java.sql.SQLException: Unknown system variable 'tx_isolation'
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1056)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:957)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3376)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3308)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1837)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1961)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2537)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2466)
    at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1383)
    at com.mysql.jdbc.ConnectionImpl.getTransactionIsolation(ConnectionImpl.java:3114)
    at com.mchange.v2.c3p0.impl.NewPooledConnection.(NewPooledConnection.java:104)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:198)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)

mysql-connector-java的版本太低，数据库的版本太高 ；

需要将mysql-connector-java升级到对应版本。

 

 

java.lang.UnsupportedClassVersionError: com/mysql/cj/jdbc/Driver : Unsupported major.minor version 5

原因： 
com/mysql/cj/jdbc/Driver是6.0版本的驱动，兼容JDK8环境，不兼容JDK7环境，在基于jdk7的tomcat中编译运行会出错，在基于jdk8的tomcat中编译运行则不会出错。

解决方案： 
1、jdk7+老版5.0驱动com/mysql/jdbc/Driver 
2、jdk8+新版6.0驱动com/mysql/cj/jdbc/Driver