DBCP2 配置

官方文档：https://commons.apache.org/proper/commons-dbcp/configuration.html

下面讲的配置通常不会使用，采用默认值即可

1. maxConnLifetimeMillis，默认值为-1。当该值大于0就会判断当前时间与该PooledObject创建时间差是否大于该值，是的话会抛出异常。用于commons-dbcp的validateObject、passivateObject、activateObject，这三个方法的调用者会使用cache或finally将回收PooledObject。官方说明：The maximum lifetime in milliseconds of a connection. After this time is exceeded the connection will fail the next activation, passivation or validation test. A value of zero or less means the connection has an infinite lifetime.

//在commons-dbcp包PoolableConnectionFactoryprivate void validateLifetime(final PooledObject<PoolableConnection> p)            throws Exception {        if (maxConnLifetimeMillis > 0) {            final long lifetime = System.currentTimeMillis() - p.getCreateTime();            if (lifetime > maxConnLifetimeMillis) {                throw new LifetimeExceededException(Utils.getMessage(                        "connectionFactory.lifetimeExceeded",                        Long.valueOf(lifetime),                        Long.valueOf(maxConnLifetimeMillis)));            }        }    }public boolean validateObject(final PooledObject<PoolableConnection> p) {        try {            validateLifetime(p);            validateConnection(p.getObject());            return true;        } catch (final Exception e) {            if (log.isDebugEnabled()) {                log.debug(Utils.getMessage(                        "poolableConnectionFactory.validateObject.fail"), e);            }            return false;        }    }//在commons-pool包GenericObjectPoolpublic void returnObject(final T obj) {    ......if (getTestOnReturn()) {            if (!factory.validateObject(p)) {                try {                    destroy(p);                } catch (final Exception e) {                    swallowException(e);                }                ......            }        }}

上面代码想说明在使用完连接返回连接池时，如果有设置testOnReturn为true，则会检查，其中会检查该连接的生命时长，如果超出maxConnLifetimeMillis则回收

1. fastFailValidation，默认为false。设置为true，如果之前连接发生过某些错误（这个在下个配置说明），则再次进行验证时直接抛出异常，不再进行验证

//在commons-dbpc包PoolableConnectionpublic void validate(final String sql, int timeout) throws SQLException {        if (_fastFailValidation && _fatalSqlExceptionThrown) {            throw new SQLException(Utils.getMessage("poolableConnection.validate.fastFail"));        }    .....    //下面代码是关于验证是否可以连接上数据库，有两个方式}

1. disconnectionSqlCodes，默认为空，多个值默认采用逗号隔开。直接官方说明：Indicate that unrecoverable SQLException was thrown when using this connection.
   Such a connection should be considered broken and not pass validation in the future.

//在commons-dbcp包PoolableConnection private boolean isDisconnectionSqlException(final SQLException e) {        boolean fatalException = false;        final String sqlState = e.getSQLState();        if (sqlState != null) {            fatalException = _disconnectionSqlCodes == null ? sqlState.startsWith(Utils.DISCONNECTION_SQL_CODE_PREFIX)                    || Utils.DISCONNECTION_SQL_CODES.contains(sqlState) : _disconnectionSqlCodes.contains(sqlState);            if (!fatalException) {                final SQLException nextException = e.getNextException();                if (nextException != null && nextException != e) {                    fatalException = isDisconnectionSqlException(e.getNextException());                }            }        }        return fatalException;    }

1. 关于removeAbandonedOnBorrow、removeAbandonedOnMaintenance、removeAbandonedTimeout
   这三个配置通常不使用
   
   • removeAbandonedOnMaintenance和removeAbandonedTimeout用在evict后台线程中是否触发抛弃方法（removeAbandoned），关闭PooledObject上次使用时间超过removeAbandonedTimeout
   • removeAbandonedOnBorrow用在用池中获取连接时判断是否触发抛弃方法（removeAbandoned）

//在commons-poolGenericObjectPoolpublic T borrowObject(final long borrowMaxWaitMillis) throws Exception {        assertOpen();        final AbandonedConfig ac = this.abandonedConfig;        if (ac != null && ac.getRemoveAbandonedOnBorrow() &&                (getNumIdle() < 2) &&                (getNumActive() > getMaxTotal() - 3) ) {            removeAbandoned(ac);        }}

下星期写篇关于GenericObjectPool对池的管理