@Overridepublic Connection getConnection()throws SQLException {returnpopConnection(dataSource.getUsername(), dataSource.getPassword()).getProxyConnection();}/**
* 数据源获取连接的方法
* 根据账号密码获取连接，获取的是PooledConnection对象，这个对象是一个代理对象，他代理了真正的连接对象，
* 并对真正的连接对象做了一定的增强，具体可以参考PooledConnection#invoke方法的注释
*/private PooledConnection popConnection(String username, String password)throws SQLException {boolean countedWait =false;
PooledConnection conn = null;long t = System.currentTimeMillis();int localBadConnectionCount =0;while(conn == null){//1.加锁，PooledDataSource是线程安全的数据库连接池synchronized(state){//2.如果有空闲连接队列中有连接，直接拿队列的首个连接对象if(!state.idleConnections.isEmpty()){// Pool has available connection
conn = state.idleConnections.remove(0);if(log.isDebugEnabled()){
log.debug("Checked out connection "+ conn.getRealHashCode()+" from pool.");}}else{//3.没有空闲连接，就走这一步// Pool does not have available connection//4.没有空闲连接，并且活跃的连接小于允许活跃的连接数上限，那么就可以创建新的连接if(state.activeConnections.size()< poolMaximumActiveConnections){// Can create new connection//5.创建新的连接，创建后直接跳到commentA处的代码逻辑
conn =newPooledConnection(dataSource.getConnection(),this);if(log.isDebugEnabled()){
log.debug("Created connection "+ conn.getRealHashCode()+".");}}else{//6.没有空闲连接，并且活跃的连接处已经大于允许活跃的连接数上限，就会走到这里，此时不允许创建新的连接了// Cannot create new connection//7.不允许创建，那么就从活跃连接队列中拿一个连接（等第一个超时了就可以拿出来使用，第一个没超时后面的更加不会超时了）
PooledConnection oldestActiveConnection = state.activeConnections.get(0);//8.获取这个拿到的连接上一次检查到现在所经过的时间long longestCheckoutTime = oldestActiveConnection.getCheckoutTime();//9.检查连接是否过期，如果checkoutTimestamp到现在的时间已经大于poolMaximumCheckoutTime就过期了if(longestCheckoutTime > poolMaximumCheckoutTime){// Can claim overdue connection //10.连接已经过期，那么把这个连接从活跃队列中移除//11.修改相关的状态变量
state.claimedOverdueConnectionCount++;//累计超时时间增加
state.accumulatedCheckoutTimeOfOverdueConnections += longestCheckoutTime;//累计使用时间增加
state.accumulatedCheckoutTime += longestCheckoutTime;//12.活跃队列移除对应的连接
state.activeConnections.remove(oldestActiveConnection);//13.如果连接还有事物尚未提交，则回滚，这里条件的判断意思是连接没有开启自动提交，说明是手动提交模式，则帮他回滚这个事物if(!oldestActiveConnection.getRealConnection().getAutoCommit()){try{
oldestActiveConnection.getRealConnection().rollback();}catch(SQLException e){
log.debug("Bad connection. Could not roll back");}}//14.从拿到的连接里面获取到里面的真实的连接对象，再把这个真实的对象包装为一个PooledConnection//(每个PooledConnection里面都包装了一个真正的连接对象)
conn =newPooledConnection(oldestActiveConnection.getRealConnection(),this);//15.销毁之前的PooledConnection
oldestActiveConnection.invalidate();if(log.isDebugEnabled()){
log.debug("Claimed overdue connection "+ conn.getRealHashCode()+".");}}else{//16.如果活跃队列没有过期(第一个没有过期，说明后面的也不会过期)，那么只能等待了// (注意活跃连接不是可用连接，空闲连接才是可用连接，活跃连接是没有回收的连接，比如其他线程A在使用的连接，这个连接就是活跃连接，// 获取到之后要判断这个连接是否超时了(比如网络原因)，超时了就移除并重新设置状态，没有超时那么说明线程A还在使用，就只能等待了)// Must waittry{if(!countedWait){//连接池等待次数加1
state.hadToWaitCount++;
countedWait =true;}if(log.isDebugEnabled()){
log.debug("Waiting as long as "+ poolTimeToWait +" milliseconds for connection.");}long wt = System.currentTimeMillis();//阻塞等待被唤醒，默认最长阻塞2秒
state.wait(poolTimeToWait);//17.累加等待时间
state.accumulatedWaitTime += System.currentTimeMillis()- wt;}catch(InterruptedException e){break;}}}}//18.到这一步，理论上是拿到了一个连接了 --- commentAif(conn != null){if(conn.isValid()){//19.检查事物if(!conn.getRealConnection().getAutoCommit()){
conn.getRealConnection().rollback();}
conn.setConnectionTypeCode(assembleConnectionTypeCode(dataSource.getUrl(), username, password));
conn.setCheckoutTimestamp(System.currentTimeMillis());
conn.setLastUsedTimestamp(System.currentTimeMillis());//20.新创建的这个连接需要加到活跃队列里面，这个连接可能是空闲队列拿到的，也可能是创建新的连接,也可能是从活跃队列里面移除了一个过期的，//并把过期的PooledConnection里面的真实连接拿到包装成一个新的PooledConnection，不管是3中情况哪一种创建的，这里都需要把它加到活跃队//列，这里也说明了注释16处的说明，活跃连接不是可用连接(如果没超时那就不可用，只能等，超时的话，做一些工作之后创建一个新的是可用的)
state.activeConnections.add(conn);
state.requestCount++;
state.accumulatedRequestTime += System.currentTimeMillis()- t;}else{//21.拿到的连接不合法，抛出异常if(log.isDebugEnabled()){
log.debug("A bad connection ("+ conn.getRealHashCode()+") was returned from the pool, getting another connection.");}//相关状态修改
state.badConnectionCount++;
localBadConnectionCount++;
conn = null;if(localBadConnectionCount >(poolMaximumIdleConnections +3)){if(log.isDebugEnabled()){
log.debug("PooledDataSource: Could not get a good connection to the database.");}thrownewSQLException("PooledDataSource: Could not get a good connection to the database.");}}}}}//22.返回前进行判断，如果为null就抛出异常，按理到这一步应该是拿到连接了，为了健壮性if(conn == null){if(log.isDebugEnabled()){
log.debug("PooledDataSource: Unknown severe error condition. The connection pool returned a null connection.");}thrownewSQLException("PooledDataSource: Unknown severe error condition. The connection pool returned a null connection.");}//23.返回return conn;}
4.1.1.2 归还连接
PooledDataSource#pushConnection是归还连接的核心方法。
/**
* 数据源归还连接的方法
*/protectedvoidpushConnection(PooledConnection conn)throws SQLException {synchronized(state){//1.加锁，PooledDataSource是线程安全的数据库连接池//2.如果活跃的连接池包含这个连接，则先移除
state.activeConnections.remove(conn);//3.连接合法才有继续操作的必要if(conn.isValid()){//4.空闲连接队列未满，并且connectionTypeCode和预期的一致，那么就尝试将连接归还(expectedConnectionTypeCode标识了一个连接池的连接)if(state.idleConnections.size()< poolMaximumIdleConnections && conn.getConnectionTypeCode()== expectedConnectionTypeCode){
state.accumulatedCheckoutTime += conn.getCheckoutTime();//5.手动回滚未完成的事物if(!conn.getRealConnection().getAutoCommit()){
conn.getRealConnection().rollback();}//6.将连接加到空闲连接里面去，其实并没有创建新的连接，而是基于这个连接里面的realConnection创建了一个PooledConnection对象
PooledConnection newConn =newPooledConnection(conn.getRealConnection(),this);
state.idleConnections.add(newConn);//7.修改这个连接里面的状态变量
newConn.setCreatedTimestamp(conn.getCreatedTimestamp());
newConn.setLastUsedTimestamp(conn.getLastUsedTimestamp());//8.销毁旧的PooledConnection
conn.invalidate();if(log.isDebugEnabled()){
log.debug("Returned connection "+ newConn.getRealHashCode()+" to pool.");}//9.唤醒其他的等待获取连接的线程
state.notifyAll();}else{//10.不满足4的条件，那么这个连接就会被销毁(比如空闲队列满了或者状态不对)
state.accumulatedCheckoutTime += conn.getCheckoutTime();//11.回滚事务if(!conn.getRealConnection().getAutoCommit()){
conn.getRealConnection().rollback();}//12.关闭连接
conn.getRealConnection().close();if(log.isDebugEnabled()){
log.debug("Closed connection "+ conn.getRealHashCode()+".");}//13.将连接置为不合法
conn.invalidate();}}else{//14.不合法连接打印一下日志if(log.isDebugEnabled()){
log.debug("A bad connection ("+ conn.getRealHashCode()+") attempted to return to the pool, discarding connection.");}//15.状态变量加一
state.badConnectionCount++;}}}
privatefinal PoolState state =newPoolState(this);public PoolState getPoolState(){return state;}
4.1.1.4 pingConnection
pingConnection用于检查连接是否可用
/**
* Method to check to see if a connection is still usable
* 检查连接是否可用
*
* @param conn - the connection to check
* @return True if the connection is still usable
*/protectedbooleanpingConnection(PooledConnection conn){boolean result =true;try{//1.如果连接是关闭的或者有异常，返回false
result =!conn.getRealConnection().isClosed();}catch(SQLException e){if(log.isDebugEnabled()){
log.debug("Connection "+ conn.getRealHashCode()+" is BAD: "+ e.getMessage());}
result =false;}//2.上面的没有异常，则进一步判断if(result){//3.允许ping才进行判断if(poolPingEnabled){//4.poolPingConnectionsNotUsedFor表示多久没有使用了才去ping，getTimeElapsedSinceLastUse返回上一次使用之后到现在过去了多久，//如果上一次使用到现在时间很短，那么就不要ping，为了提高效率，因为这样的情况下大概率连接是ok的，//如果上一次使用到现在已经过去很久了，大于poolPingConnectionsNotUsedFor这个阈值，那么就很有必要检查下这个连接了//这里也能看出，如果poolPingConnectionsNotUsedFor小于0，说明任何时候都不会去真正的ping服务器if(poolPingConnectionsNotUsedFor >=0&& conn.getTimeElapsedSinceLastUse()> poolPingConnectionsNotUsedFor){try{if(log.isDebugEnabled()){
log.debug("Testing connection "+ conn.getRealHashCode()+" ...");}//5.这里可以看出，其实就是执行了poolPingQuery这个sql语句，如果有异常，则方法返回false，默认是没有设置这个语句//的-->"NO PING QUERY SET"
Connection realConn = conn.getRealConnection();
Statement statement = realConn.createStatement();
ResultSet rs = statement.executeQuery(poolPingQuery);
rs.close();
statement.close();if(!realConn.getAutoCommit()){
realConn.rollback();}
result =true;if(log.isDebugEnabled()){
log.debug("Connection "+ conn.getRealHashCode()+" is GOOD!");}}catch(Exception e){//6.如果没有设置poolPingQuery，这里就报异常，内部进行了异常捕获处理
log.warn("Execution of ping query '"+ poolPingQuery +"' failed: "+ e.getMessage());try{
conn.getRealConnection().close();}catch(Exception e2){//ignore}
result =false;if(log.isDebugEnabled()){
log.debug("Connection "+ conn.getRealHashCode()+" is BAD: "+ e.getMessage());}}}}}return result;}
4.1.1.5 forceCloseAll
forceCloseAll用于强制关闭所有的活跃队列连接和空闲队列连接
/*
* Closes all active and idle connections in the pool
* 强制关闭所有的活跃队列连接和空闲队列连接
*/publicvoidforceCloseAll(){//1.同步加锁synchronized(state){
expectedConnectionTypeCode =assembleConnectionTypeCode(dataSource.getUrl(), dataSource.getUsername(), dataSource.getPassword());//2.关闭活跃队列内的连接for(int i = state.activeConnections.size(); i >0; i--){try{
PooledConnection conn = state.activeConnections.remove(i -1);//2.1销毁PooledConnection
conn.invalidate();//2.2回滚事物
Connection realConn = conn.getRealConnection();if(!realConn.getAutoCommit()){
realConn.rollback();}//2.3关闭realConnection
realConn.close();}catch(Exception e){// ignore}}//3.关闭空闲队列内的连接for(int i = state.idleConnections.size(); i >0; i--){try{
PooledConnection conn = state.idleConnections.remove(i -1);//3.1销毁PooledConnection
conn.invalidate();//3.2回滚事物
Connection realConn = conn.getRealConnection();if(!realConn.getAutoCommit()){
realConn.rollback();}//3.3关闭realConnection
realConn.close();}catch(Exception e){// ignore}}}if(log.isDebugEnabled()){
log.debug("PooledDataSource forcefully closed/removed all connections.");}}
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