通过Druid连接池获取Connection

从DataSource.getConnection入手来看一下通过druid获取连接时的内部逻辑。

首先进入DruidDataSource的这个方法

public DruidPooledConnection getConnection(long maxWaitMillis) throws SQLException {
       //初始化连接 数量为设置的InitilSize,如果没有配置则为0，MaxActive最大为8 
       init();
　　　　　//　如果有FilterChain,走FilterChain的逻辑
        if (filters.size() > 0) {
            FilterChainImpl filterChain = new FilterChainImpl(this);
            return filterChain.dataSource_connect(this, maxWaitMillis);
        } else {
　　　　　　　//真正的获取连接的方法
            return getConnectionDirect(maxWaitMillis);
        }
    }

正常情况下通过getConnectionDirect来直接获取连接，里面传了一个最大等待时间，稍后我们分析这个参数的作用。

先看上部分逻辑：

     int notFullTimeoutRetryCnt = 0;
        for (;;) {
            // handle notFullTimeoutRetry
            DruidPooledConnection poolableConnection;
            try {
                poolableConnection = getConnectionInternal(maxWaitMillis);
            } catch (GetConnectionTimeoutException ex) {
                if (notFullTimeoutRetryCnt <= this.notFullTimeoutRetryCount && !isFull()) {
                    notFullTimeoutRetryCnt++;
                    if (LOG.isWarnEnabled()) {
                        LOG.warn("get connection timeout retry : " + notFullTimeoutRetryCnt);
                    }
                    continue;
                }
                throw ex;
            }

这一部分很好理解，一个for循环里面通过getConnectionInternal(maxWaitMillis)方法来获取一个真实的物理连接，

如果捕捉到获取连接超时的异常，去判断notFullTimeoutRetryCnt 这个参数是否小于设定的超时重试参数，并且

在连接池未满的情况下继续进行重试。如果重试次数已经足够或者此时连接池已经满了(其它线程获取到连接)则

将异常抛出去。isFull方法用来判断存在池子内的连接和活跃连接(已经被线程brrow走了)的数量是否大于等于最大

连接数MaxActiveCount。

进入getConnectionInternal内部：

 private DruidPooledConnection getConnectionInternal(long maxWait) throws SQLException {
        //如果当前连接池已经关闭 则抛出异常
        if (closed) {
            connectErrorCountUpdater.incrementAndGet(this);
            throw new DataSourceClosedException("dataSource already closed at " + new Date(closeTimeMillis));
        }
　　　　　//如果当期连接池状态为不可用 则抛出异常　
        if (!enable) {
            connectErrorCountUpdater.incrementAndGet(this);

            if (disableException != null) {
                throw disableException;
            }

            throw new DataSourceDisableException();
        }

        final long nanos = TimeUnit.MILLISECONDS.toNanos(maxWait);
        final int maxWaitThreadCount = this.maxWaitThreadCount;

        DruidConnectionHolder holder;

        for (boolean createDirect = false;;) {
            if (createDirect) {
                createStartNanosUpdater.set(this, System.nanoTime());
                if (creatingCountUpdater.compareAndSet(this, 0, 1)) {
                    PhysicalConnectionInfo pyConnInfo = DruidDataSource.this.createPhysicalConnection();
                    holder = new DruidConnectionHolder(this, pyConnInfo);
                    holder.lastActiveTimeMillis = System.currentTimeMillis();

                    creatingCountUpdater.decrementAndGet(this);
                    directCreateCountUpdater.incrementAndGet(this);

                    if (LOG.isDebugEnabled()) {
                        LOG.debug("conn-direct_create ");
                    }

                    boolean discard = false;
                    lock.lock();
                    try {
                        if (activeCount < maxActive) {
                            activeCount++;
                            holder.active = true;
                            if (activeCount > activePeak) {
                                activePeak = activeCount;
                                activePeakTime = System.currentTimeMillis();
                            }
                            break;
                        } else {
                            discard = true;
                        }
                    } finally {
                        lock.unlock();
                    }

                    if (discard) {
                        JdbcUtils.close(pyConnInfo.getPhysicalConnection());
                    }
                }
            }

            try {
                lock.lockInterruptibly();
            } catch (InterruptedException e) {
                connectErrorCountUpdater.incrementAndGet(this);
                throw new SQLException("interrupt", e);
            }

            try {
                if (maxWaitThreadCount > 0
                        && notEmptyWaitThreadCount >= maxWaitThreadCount) {
                    connectErrorCountUpdater.incrementAndGet(this);
                    throw new SQLException("maxWaitThreadCount " + maxWaitThreadCount + ", current wait Thread count "
                            + lock.getQueueLength());
                }

                if (onFatalError
                        && onFatalErrorMaxActive > 0
                        && activeCount >= onFatalErrorMaxActive) {
                    connectErrorCountUpdater.incrementAndGet(this);

                    StringBuilder errorMsg = new StringBuilder();
                    errorMsg.append("onFatalError, activeCount ")
                            .append(activeCount)
                            .append(", onFatalErrorMaxActive ")
                            .append(onFatalErrorMaxActive);

                    if (lastFatalErrorTimeMillis > 0) {
                        errorMsg.append(", time '")
                                .append(StringUtils.formatDateTime19(
                                        lastFatalErrorTimeMillis, TimeZone.getDefault()))
                                .append("'");
                    }

                    if (lastFatalErrorSql != null) {
                        errorMsg.append(", sql \n")
                                .append(lastFatalErrorSql);
                    }

                    throw new SQLException(
                            errorMsg.toString(), lastFatalError);
                }

                connectCount++;

                if (createScheduler != null
                        && poolingCount == 0
                        && activeCount < maxActive
                        && creatingCountUpdater.get(this) == 0
                        && createScheduler instanceof ScheduledThreadPoolExecutor) {
                    ScheduledThreadPoolExecutor executor = (ScheduledThreadPoolExecutor) createScheduler;
                    if (executor.getQueue().size() > 0) {
                        createDirect = true;
                        continue;
                    }
                }

                if (maxWait > 0) {
                    holder = pollLast(nanos);
                } else {
                    holder = takeLast();
                }

                if (holder != null) {
                    if (holder.discard) {
                        continue;
                    }

                    activeCount++;
                    holder.active = true;
                    if (activeCount > activePeak) {
                        activePeak = activeCount;
                        activePeakTime = System.currentTimeMillis();
                    }
                }
            } catch (InterruptedException e) {
                connectErrorCountUpdater.incrementAndGet(this);
                throw new SQLException(e.getMessage(), e);
            } catch (SQLException e) {
                connectErrorCountUpdater.incrementAndGet(this);
                throw e;
            } finally {
                lock.unlock();
            }

            break;
        }

        if (holder == null) {
            long waitNanos = waitNanosLocal.get();

            StringBuilder buf = new StringBuilder(128);
            buf.append("wait millis ")//
               .append(waitNanos / (1000 * 1000))//
               .append(", active ").append(activeCount)//
               .append(", maxActive ").append(maxActive)//
               .append(", creating ").append(creatingCount)//
            ;
            if (creatingCount > 0 && createStartNanos > 0) {
                long createElapseMillis = (System.nanoTime() - createStartNanos) / (1000 * 1000);
                if (createElapseMillis > 0) {
                    buf.append(", createElapseMillis ").append(createElapseMillis);
                }
            }

            if (createErrorCount > 0) {
                buf.append(", createErrorCount ").append(createErrorCount);
            }

            List<JdbcSqlStatValue> sqlList = this.getDataSourceStat().getRuningSqlList();
            for (int i = 0; i < sqlList.size(); ++i) {
                if (i != 0) {
                    buf.append('\n');
                } else {
                    buf.append(", ");
                }
                JdbcSqlStatValue sql = sqlList.get(i);
                buf.append("runningSqlCount ").append(sql.getRunningCount());
                buf.append(" : ");
                buf.append(sql.getSql());
            }

            String errorMessage = buf.toString();

            if (this.createError != null) {
                throw new GetConnectionTimeoutException(errorMessage, createError);
            } else {
                throw new GetConnectionTimeoutException(errorMessage);
            }
        }

        holder.incrementUseCount();

        DruidPooledConnection poolalbeConnection = new DruidPooledConnection(holder);
        return poolalbeConnection;