public DruidPooledConnection getConnection(long maxWaitMillis) throws SQLException {
　　　　 //初始化檢查配置和后臺(tái)線程
        init();

        if (filters.size() > 0) {
            FilterChainImpl filterChain = new FilterChainImpl(this);
            return filterChain.dataSource_connect(this, maxWaitMillis);
        } else {
            return getConnectionDirect(maxWaitMillis);
        }
    }

decrementPoolingCount();
DruidConnectionHolder last = connections[poolingCount];
connections[poolingCount] = null;

DruidPooledConnection poolalbeConnection = new DruidPooledConnection(holder);

public DruidPooledConnection(DruidConnectionHolder holder){
        super(holder.getConnection());

        this.conn = holder.getConnection();
        this.holder = holder;
        this.lock = holder.lock;
        dupCloseLogEnable = holder.getDataSource().isDupCloseLogEnable();
        ownerThread = Thread.currentThread();
        connectedTimeMillis = System.currentTimeMillis();
}

long idleMillis  = currentTimeMillis - lastActiveTimeMillis;

long timeBetweenEvictionRunsMillis = this.timeBetweenEvictionRunsMillis;

if (timeBetweenEvictionRunsMillis <= 0) {
      timeBetweenEvictionRunsMillis = DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS;
}

if (idleMillis >= timeBetweenEvictionRunsMillis
        || idleMillis < 0 // unexcepted branch
         ) {
     boolean validate = testConnectionInternal(poolableConnection.holder, poolableConnection.conn);
     if (!validate) {
        if (LOG.isDebugEnabled()) {
             LOG.debug("skip not validate connection.");
        }

        discardConnection(poolableConnection.holder);
        continue;
        }
}

long timeMillis = (currrentNanos - pooledConnection.getConnectedTimeNano()) / (1000 * 1000);

if (timeMillis >= removeAbandonedTimeoutMillis) {
    iter.remove();
    pooledConnection.setTraceEnable(false);
    abandonedList.add(pooledConnection);
}

if (phyTimeoutMillis > 0) {
    long phyConnectTimeMillis = currentTimeMillis - holder.connectTimeMillis;
    if (phyConnectTimeMillis > phyTimeoutMillis) {
          discardConnection(holder);
          return;
    }
}
lock.lock();
try {
    if (holder.active) {
        activeCount--;
        holder.active = false;
    }
    closeCount++;

    result = putLast(holder, currentTimeMillis);
    recycleCount++;
} finally {
    lock.unlock();
}

boolean putLast(DruidConnectionHolder e, long lastActiveTimeMillis) {
        if (poolingCount >= maxActive || e.discard) {
            return false;
        }

        e.lastActiveTimeMillis = lastActiveTimeMillis;
        connections[poolingCount] = e;
        incrementPoolingCount();

        if (poolingCount > poolingPeak) {
            poolingPeak = poolingCount;
            poolingPeakTime = lastActiveTimeMillis;
        }

        notEmpty.signal();
        notEmptySignalCount++;

        return true;
}

private void init() throws ConnectionPoolException
{　　　　
     if ( LOGGER.isTraceEnabled() ) LOGGER.logTrace ( this + ": initializing..." );　　　//如果連接池最小連接數(shù)沒有達(dá)到就新增數(shù)據(jù)庫連接
     addConnectionsIfMinPoolSizeNotReached();　　  //開啟維持連接池平衡的線程
     launchMaintenanceTimer();
}

private void launchMaintenanceTimer() {
        int maintenanceInterval = properties.getMaintenanceInterval();
        if ( maintenanceInterval <= 0 ) {
            if ( LOGGER.isTraceEnabled() ) LOGGER.logTrace ( this + ": using default maintenance interval..." );
            maintenanceInterval = DEFAULT_MAINTENANCE_INTERVAL;
        }
        maintenanceTimer = new PooledAlarmTimer ( maintenanceInterval * 1000 );
        maintenanceTimer.addAlarmTimerListener(new AlarmTimerListener() {
            public void alarm(AlarmTimer timer) {
                reapPool();　　　　　　　　　 //如果達(dá)到了最大的存活時(shí)間就移除該連接
                removeConnectionsThatExceededMaxLifetime();　　　　　　　　　 //如果沒有滿足最小連接數(shù)就新增連接
                addConnectionsIfMinPoolSizeNotReached();　　　　　　　　   //移除超過最小連接數(shù)以外的連接
                removeIdleConnectionsIfMinPoolSizeExceeded();
            }
        });
        TaskManager.SINGLETON.executeTask ( maintenanceTimer );
    }

private synchronized void removeConnectionsThatExceededMaxLifetime()
    {
        long maxLifetime = properties.getMaxLifetime();
        if ( connections == null || maxLifetime <= 0 ) return;

        if ( LOGGER.isTraceEnabled() ) LOGGER.logTrace ( this + ": closing connections that exceeded maxLifetime" );

        Iterator<XPooledConnection> it = connections.iterator();
        while ( it.hasNext() ) {
            XPooledConnection xpc = it.next();
            long creationTime = xpc.getCreationTime();
            long now = System.currentTimeMillis();
            if ( xpc.isAvailable() &&  ( (now - creationTime) >= (maxLifetime * 1000L) ) ) {
                if ( LOGGER.isTraceEnabled() ) LOGGER.logTrace ( this + ": connection in use for more than " + maxLifetime + "s, destroying it: " + xpc );　　　　　　　　　 //如果超過最大的存活時(shí)間就銷毀該連接
                destroyPooledConnection(xpc);
                it.remove();
            }
        }
        logCurrentPoolSize();
    }