今天在进行本机的数据库连接的时候出现了一个问题：

Caused by: java.sql.SQLException: Unknown system variable ‘tx_isolation’

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1055)

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423)

at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2536)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2465)

at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1383)

at com.mysql.jdbc.ConnectionImpl.getTransactionIsolation(ConnectionImpl.java:3117)

at com.mchange.v2.c3p0.impl.NewPooledConnection.<init>(NewPooledConnection.java:120)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:240)

at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:206)

at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:203)

at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1138)

at com.mchange.v2.resourcepool.BasicResourcePool.doAcquireAndDecrementPendingAcquiresWithinLockOnSuccess(BasicResourcePool.java:1125)

at com.mchange.v2.resourcepool.BasicResourcePool.access$700(BasicResourcePool.java:44)

at com.mchange.v2.resourcepool.BasicResourcePool$ScatteredAcquireTask.run(BasicResourcePool.java:1870)

at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:696)

一开始以为是隔离级别的问题，但是最终排查出来了问题是mysql-connector-java的版本太低，数据库的版本太高 因此将mysql-connector-java升级到最新版本就解决了问题.