使用C3p0连接池时，在空闲状态一直DEBUG打印如下日志，好像是一直在创建并销毁连接，要怎样配置才能够不一直创建销毁,创建后就保留起，如果连接不够再创建。
DEBUG c.m.v.resourcepool.BasicResourcePool - Preparing to destroy resource: com.mchange.v2.c3p0.impl.NewPooledConnection@4ae0cd66
DEBUG c.m.v.c.i.C3P0PooledConnectionPool - Preparing to destroy PooledConnection: com.mchange.v2.c3p0.impl.NewPooledConnection@4ae0cd66
DEBUG c.m.v.c.i.C3P0PooledConnectionPool - Successfully destroyed PooledConnection: com.mchange.v2.c3p0.impl.NewPooledConnection@4ae0cd66
DEBUG c.m.v.resourcepool.BasicResourcePool - Successfully destroyed resource: com.mchange.v2.c3p0.impl.NewPooledConnection@4ae0cd66
DEBUG c.m.v.resourcepool.BasicResourcePool - Checking for expired resources - Fri Sep 27 16:18:25 CST 2019 [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - BEGIN check for expired resources. [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - FINISHED check for expired resources. [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - Checking for expired resources - Fri Sep 27 16:18:26 CST 2019 [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - BEGIN check for expired resources. [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - EXPIRED idle resource: com.mchange.v2.c3p0.impl.NewPooledConnection@34b92a30 ---> idle_time: 1966; max_idle_time: 1000 [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - Removing expired resource: com.mchange.v2.c3p0.impl.NewPooledConnection@34b92a30 [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - FINISHED check for expired resources. [com.mchange.v2.resourcepool.BasicResourcePool@2794eab6]
DEBUG c.m.v.resourcepool.BasicResourcePool - Preparing to destroy resource: com.mchange.v2.c3p0.impl.NewPooledConnection@34b92a30
DEBUG c.m.v.c.i.C3P0PooledConnectionPool - Preparing to destroy PooledConnection: com.mchange.v2.c3p0.impl.NewPooledConnection@34b92a30
DEBUG c.m.v.c.i.C3P0PooledConnectionPool - Successfully destroyed PooledConnection: com.mchange.v2.c3p0.impl.NewPooledConnection@34b92a30
DEBUG c.m.v.resourcepool.BasicResourcePool - Successfully destroyed resource: com.mchange.v2.c3p0.impl.NewPooledConnection@34b92a30
