问题现象：
使用Druid的数据库连接池，在进行一个查询SQL的时候，抛出了异常：
[2017-10-20 01:40:59.269 ERROR com.alibaba.druid.pool.DruidDataSource:2189] abandon connection, owner thread: schedulerDuty_Worker-2, connected at : 1508434843057, open stackTrace
at java.lang.Thread.getStackTrace(Thread.java:1552)
at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:1068)
at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4544)
at com.alibaba.druid.filter.stat.StatFilter.dataSource_getConnection(StatFilter.java:662)
at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4540)
at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:992)
at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:984)
at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:103)
at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111)
at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77)
at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:84)
at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:70)
at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:336)
at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:84)
at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62)
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77)
at sun.reflect.GeneratedMethodAccessor696.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:434)
at com.sun.proxy.$Proxy61.selectOne(Unknown Source)
at org.mybatis.spring.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:167)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:82)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
at com.sun.proxy.$Proxy83.isStatisticExist(Unknown Source)
at org.quartz.core.JobRunShell.run(JobRunShell.java:202)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:573)
ownerThread current state is RUNNABLE, current stackTrace
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:170)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:145)
at org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:145)
at org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:114)
at org.postgresql.core.VisibleBufferedInputStream.read(VisibleBufferedInputStream.java:73)
at org.postgresql.core.PGStream.ReceiveChar(PGStream.java:274)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1661)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:257)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:512)
at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:374)
at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:366)
at com.alibaba.druid.filter.FilterChainImpl.statement_execute(FilterChainImpl.java:2489)
at com.alibaba.druid.filter.FilterAdapter.statement_execute(FilterAdapter.java:2451)
at com.alibaba.druid.filter.FilterEventAdapter.statement_execute(FilterEventAdapter.java:188)
at com.alibaba.druid.filter.FilterChainImpl.statement_execute(FilterChainImpl.java:2487)
at com.alibaba.druid.proxy.jdbc.StatementProxyImpl.execute(StatementProxyImpl.java:137)
at com.alibaba.druid.pool.DruidPooledStatement.execute(DruidPooledStatement.java:416)
at org.apache.ibatis.executor.statement.SimpleStatementHandler.query(SimpleStatementHandler.java:73)
at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79)
at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:63)
at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77)
at sun.reflect.GeneratedMethodAccessor696.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:434)
at com.sun.proxy.$Proxy61.selectOne(Unknown Source)
at org.mybatis.spring.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:167)
at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:82)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:53)
at com.sun.proxy.$Proxy83.isExist(Unknown Source)
从报错信息中可以提取到，是Druid连接池执行SQL，获取Statement失败，导致的问题
问题分析：根据异常的第一行，可以得知报错来自于DruidDataSource这个类，根据报错的信息，可以看出是因为执行SQL时获取不到Connection连接，然后去看一下Druid的配置中，有三个配置可以关注一下：
配置默认值说明removeAbandonedfalse是否强制关闭连接时长大于removeAbandonedTimeoutMillis的连接removeAbandonedTimeoutMillis300 * 1000一个连接从被连接到被关闭之间的最大生命周期logAbandonedfalse强制关闭连接时是否记录日志再去查看我们的配置，removeAbandoned是true，代表的意思是 是否关闭连接时长大于一定时长的连接，问题可能是出在这里，去看源代码：
public class DestroyTask implements Runnable {
public DestroyTask() {
}
public void run() {
DruidDataSource.this.shrink(true);
if(DruidDataSource.this.isRemoveAbandoned()) {
DruidDataSource.this.removeAbandoned();
}
}
}
发现调用removeAbandoned的位置在这里，这里是一个线程，在连接池初始化的时候会启动一个调度，在定时的时间频度去执行，可以看出这里的判断条件是如果开启了配置，就去执行removeAbandoned()这个方法，来看一下这个方法里面有什么：
public int removeAbandoned() {
int removeCount = 0;
long currrentNanos = System.nanoTime();
ArrayList abandonedList = new ArrayList();
Map var5 = this.activeConnections;
synchronized(this.activeConnections) {
Iterator pooledConnection = this.activeConnections.keySet().iterator();
while(pooledConnection.hasNext()) {
DruidPooledConnection buf = (DruidPooledConnection)pooledConnection.next();
if(!buf.isRunning()) {
long trace = (currrentNanos - buf.getConnectedTimeNano()) / 1000000L;
if(trace >= this.removeAbandonedTimeoutMillis) {
pooledConnection.remove();
buf.setTraceEnable(false);
abandonedList.add(buf);
}
}
}
}
.................
}
这里给出了一部分的代码实现，可以看到问题的原因可能就是出现在这里了，这里进行了一个判断，循环遍历连接池中的连接，如果存活，就判断是否超过了配置的removeAbandonedTimeoutMillis（单位是毫秒，配置里面需要配置秒，有转换），如果超过了时间，我就干死你！
解决方案问题原因已经找到，那么解决的办法就是将removeAbandoned这个配置设置为false或者不设置（默认就是false），或者将removeAbandonedTimeoutMillis这个时间配置调大：
再观察，就不会出现报错的情况了，问题解决~
官方说明：
https://github.com/alibaba/druid/wiki/%E8%BF%9E%E6%8E%A5%E6%B3%84%E6%BC%8F%E7%9B%91%E6%B5%8B
