Alibaba Druid 源码阅读（三） 数据库连接池初始化探索

public void init() throws SQLException {        // 已经初始化过了，直接返回        if (inited) {            return;        }
        // bug fixed for dead lock, for issue #2980        DruidDriver.getInstance();
        // 初始化时上锁        final ReentrantLock lock = this.lock;        try {            lock.lockInterruptibly();        } catch (InterruptedException e) {            throw new SQLException("interrupt", e);        }
        boolean init = false;        try {            if (inited) {                return;            }
            initStackTrace = Utils.toString(Thread.currentThread().getStackTrace());
            // 这部分尚不清楚作用            this.id = DruidDriver.createDataSourceId();            if (this.id > 1) {                long delta = (this.id - 1) * 100000;                this.connectionIdSeedUpdater.addAndGet(this, delta);                this.statementIdSeedUpdater.addAndGet(this, delta);                this.resultSetIdSeedUpdater.addAndGet(this, delta);                this.transactionIdSeedUpdater.addAndGet(this, delta);            }
            // 数据库连接url            if (this.jdbcUrl != null) {                this.jdbcUrl = this.jdbcUrl.trim();                initFromWrapDriverUrl();            }
            // filter相关，目前为空            for (Filter filter : filters) {                filter.init(this);            }
            // 获取数据库类型            if (this.dbTypeName == null || this.dbTypeName.length() == 0) {                this.dbTypeName = JdbcUtils.getDbType(jdbcUrl, null);            }
            // 针对 mysql、mariadb、oceanbase、ads 做其特有的处理            DbType dbType = DbType.of(this.dbTypeName);            if (dbType == DbType.mysql                    || dbType == DbType.mariadb                    || dbType == DbType.oceanbase                    || dbType == DbType.ads) {                boolean cacheServerConfigurationSet = false;                if (this.connectProperties.containsKey("cacheServerConfiguration")) {                    cacheServerConfigurationSet = true;                } else if (this.jdbcUrl.indexOf("cacheServerConfiguration") != -1) {                    cacheServerConfigurationSet = true;                }                if (cacheServerConfigurationSet) {                    this.connectProperties.put("cacheServerConfiguration", "true");                }            }
            // 下面就是一些配置的效验            // 这部分是不是放到最前面比较好？            if (maxActive <= 0) {                throw new IllegalArgumentException("illegal maxActive " + maxActive);            }
            if (maxActive < minIdle) {                throw new IllegalArgumentException("illegal maxActive " + maxActive);            }
            if (getInitialSize() > maxActive) {                throw new IllegalArgumentException("illegal initialSize " + this.initialSize + ", maxActive " + maxActive);            }
            if (timeBetweenLogStatsMillis > 0 && useGlobalDataSourceStat) {                throw new IllegalArgumentException("timeBetweenLogStatsMillis not support useGlobalDataSourceStat=true");            }
            if (maxEvictableIdleTimeMillis < minEvictableIdleTimeMillis) {                throw new SQLException("maxEvictableIdleTimeMillis must be grater than minEvictableIdleTimeMillis");            }
            if (keepAlive && keepAliveBetweenTimeMillis <= timeBetweenEvictionRunsMillis) {                throw new SQLException("keepAliveBetweenTimeMillis must be grater than timeBetweenEvictionRunsMillis");            }
            // driverClass相关            if (this.driverClass != null) {                this.driverClass = driverClass.trim();            }
            // 下面这段有些初始化加载和检查，但不是看的太明白            initFromSPIServiceLoader();
            resolveDriver();
            initCheck();
            initExceptionSorter();            initValidConnectionChecker();            validationQueryCheck();
            // Stat 的作用是啥，目前尚不清楚            if (isUseGlobalDataSourceStat()) {                dataSourceStat = JdbcDataSourceStat.getGlobal();                if (dataSourceStat == null) {                    dataSourceStat = new JdbcDataSourceStat("Global", "Global", this.dbTypeName);                    JdbcDataSourceStat.setGlobal(dataSourceStat);                }                if (dataSourceStat.getDbType() == null) {                    dataSourceStat.setDbType(this.dbTypeName);                }            } else {                dataSourceStat = new JdbcDataSourceStat(this.name, this.jdbcUrl, this.dbTypeName, this.connectProperties);            }            dataSourceStat.setResetStatEnable(this.resetStatEnable);
            // 关键的数据库连接池相关的，在获取连接中就是从DruidConnectionHolder中获取的            connections = new DruidConnectionHolder[maxActive];            evictConnections = new DruidConnectionHolder[maxActive];            keepAliveConnections = new DruidConnectionHolder[maxActive];
            SQLException connectError = null;
            // 这段看大致意思的异步去生成数据库物理连接            // 因为else中是可以看出直接获取了数据库的物理连接，然后放到DruidConnectionHolder中            if (createScheduler != null && asyncInit) {                for (int i = 0; i < initialSize; ++i) {                    submitCreateTask(true);                }            } else if (!asyncInit) {                // init connections                while (poolingCount < initialSize) {                    try {                        PhysicalConnectionInfo pyConnectInfo = createPhysicalConnection();                        DruidConnectionHolder holder = new DruidConnectionHolder(this, pyConnectInfo);                        connections[poolingCount++] = holder;                    } catch (SQLException ex) {                        LOG.error("init datasource error, url: " + this.getUrl(), ex);                        if (initExceptionThrow) {                            connectError = ex;                            break;                        } else {                            Thread.sleep(3000);                        }                    }                }
                if (poolingCount > 0) {                    poolingPeak = poolingCount;                    poolingPeakTime = System.currentTimeMillis();                }            }
            // 一些辅助性，日志啥的初始化操作            createAndLogThread();            createAndStartCreatorThread();            createAndStartDestroyThread();
            initedLatch.await();            init = true;
            initedTime = new Date();            registerMbean();
            if (connectError != null && poolingCount == 0) {                throw connectError;            }
            // 前面使用的是initialSize 初始连接数            // 这个使用的是 keepAlive 看着意思是空闲连接数            if (keepAlive) {                // async fill to minIdle                if (createScheduler != null) {                    for (int i = 0; i < minIdle; ++i) {                        submitCreateTask(true);                    }                } else {                    this.emptySignal();                }            }
        } catch (SQLException e) {            LOG.error("{dataSource-" + this.getID() + "} init error", e);            throw e;        } catch (InterruptedException e) {            throw new SQLException(e.getMessage(), e);        } catch (RuntimeException e){            LOG.error("{dataSource-" + this.getID() + "} init error", e);            throw e;        } catch (Error e){            LOG.error("{dataSource-" + this.getID() + "} init error", e);            throw e;
        } finally {            inited = true;            lock.unlock();
            if (init && LOG.isInfoEnabled()) {                String msg = "{dataSource-" + this.getID();
                if (this.name != null && !this.name.isEmpty()) {                    msg += ",";                    msg += this.name;                }
                msg += "} inited";
                LOG.info(msg);            }        }    }