在工程中使用了druid连接池，运行一段时间后系统出现异常：
- Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is com.alibaba.druid.pool.GetConnectionTimeoutException: wait millis 60009, active 50
- at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:80)
- at org.springframework.jdbc.support.JdbcUtils.extractDatabaseMetaData(JdbcUtils.java:280)
- ... 64 more
- Caused by: com.alibaba.druid.pool.GetConnectionTimeoutException: wait millis 60000, active 50
- at com.alibaba.druid.pool.DruidDataSource.getConnectionInternal(DruidDataSource.java:1071)
- at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:898)
- at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4544)
mysql数据库最大连接数设置为500，使用客户端能正常连接。连接数被未被占满。
分析原因应该是程序中有地方连接未关闭造成的。那如何来定呢？使用druid连接池的超时回收机制，在配置中增加以下内容：
- <!-- 超过时间限制是否回收 -->
- <property name="removeAbandoned" value="true" />
- <!-- 超时时间；单位为秒。180秒=3分钟 -->
- <property name="removeAbandonedTimeout" value="180" />
- <!-- 关闭abanded连接时输出错误日志 -->
- <property name="logAbandoned" value="true" />
运行程序，当连接超过3分钟后会强制进行回收，并输出异常日志。
- 2014-10-13 16:02:28,919 ERROR [com.alibaba.druid.pool.DruidDataSource] - <abandon connection, open stackTrace
- at java.lang.Thread.getStackTrace(Thread.java:1567)
- at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:995)
- at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4544)
- at com.alibaba.druid.filter.stat.StatFilter.dataSource_getConnection(StatFilter.java:661)
- at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4540)
- at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:919)
- at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:911)
- at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:98)
- at cn.org.xxx.xxx.xxx.PaginationInterceptor.intercept(PaginationInterceptor.java:96)
- at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:60)
- at com.sun.proxy.$Proxy59.query(Unknown Source)
- at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:108)
很清楚地看到是在哪里打开的连接未关闭一直在占有。
此配置项会影响性能，只在排查的时候打开。系统运行时最好关闭。