一、目標

? ? ? ? ? 用精簡的代碼實現一個類似于Hikari，Druid一樣的高性能數據庫連接池。

二、實現思路

? ? ? ?1:新建連接池配置類保存連接池配置。

? ? ? ?2:實現DataSource接口。

? ? ? ?3:新增SmpDbPool類，內部維護一個阻塞隊列保存數據庫連接，并提供數據庫連接的獲取回收等方法。

? ? ? ?4:大致類圖:

三、核心代碼

1:數據庫連接代理類SmpConnectionProxy

SmpConnectionProxy實現jdbc的Connection接口

重寫close方法，確保外部調用close的時候將連接歸還到連接池。

public void close() throws SQLException {if (this.closed) return;this.closed = true;//回滾掉未提交的臟statementif (this.isCommitStateDirty && !this.isAutoCommit){this.delegate.rollback();//}this.clearWarnings();this.smpDbPool.releaseConnection(this);}

新增判斷連接是否有效方法供連接池類使用。

public boolean isValid() throws SQLException {if (System.currentTimeMillis() - this.lastActiveTime < this.smpDbPool.getConfig().getKeepaliveTimeInMill()) return true;long validationTimeout = this.smpDbPool.getConfig().getValidationTimeoutInMill();this.delegate.setNetworkTimeout(this.smpDbPool.getNetTimeoutExecutor(), (int) validationTimeout);int validationSeconds = (int) Math.max(1000L, validationTimeout) / 1000;return this.delegate.isValid(validationSeconds);}

2:數據源類SmpDataSource

SmpDataSource實現DataSource接口

實現getConnection方法，以便外界從連接池獲取連接。

@Overridepublic Connection getConnection() throws SQLException {try {return this.dbPool.borrowConnection();} catch (Exception e) {LOG.error("getConnection error", e);throw new SQLException(e);}}

3:連接池類SmpDbPool

獲取數據庫連接方法:

public Connection borrowConnection() throws Exception {boolean isDebugEnable = LOG.isDebugEnabled();long sTime = 0;if (isDebugEnable){//盡量少訪問臨界資源sTime = System.currentTimeMillis();}try {SmpConnectionProxy connection = this.getConnectionFromQueue();if (connection != null) return connection;//未獲取到有效連接,校驗是否創建連接int maxActive = this.smpConfig.getMaxActive(), dbAmount = createdDbConnectionAmount.get();if (dbAmount >= maxActive){//嘗試等待其他線程釋放連接connection = this.dbConnectQueue.poll(this.smpConfig.getMaxWaitInMill(), TimeUnit.MILLISECONDS);if (connection != null) return connection.borrowConnection();LOG.error("get connection error, no connection available,maxActive:{}, activated connection:{}", maxActive, dbAmount);throw new IllegalStateException("database connection pool too busy");}connection = this.createConnectionForPool();if (connection != null) return connection;throw new IllegalStateException("database connection pool too busy");} finally {if (isDebugEnable){LOG.debug("get database connection cost {} ms", System.currentTimeMillis() - sTime);}}}

從阻塞隊列獲取數據庫連接方法:

private SmpConnectionProxy getConnectionFromQueue() throws SQLException {int times = 0;while (times++ < 1000){SmpConnectionProxy connection = this.dbConnectQueue.poll();if (connection == null) return null;if (connection.isValid()) return connection.borrowConnection();//destroy invalid connectionconnection.destroy();createdDbConnectionAmount.decrementAndGet();LOG.info("destroyed invalid jdbc connection");}return null;}

新建數據庫連接:

private SmpConnectionProxy createConnectionForPool() throws Exception{boolean locked = false;try {locked = GET_CONNECTION_LOCK.tryLock(this.smpConfig.getMaxWaitInMill() >> 1, TimeUnit.MILLISECONDS);if (!locked){LOG.error("get lock to create connection error");return null;}SmpConnectionProxy connection = this.getConnectionFromQueue();if (connection != null) return connection;int dbAmount = createdDbConnectionAmount.get(), maxActive = this.smpConfig.getMaxActive();if (dbAmount >= maxActive){LOG.error("get connection error, no connection available,maxActive:{}, activated connection:{}", maxActive, dbAmount);return null;}connection = this.createConnection();createdDbConnectionAmount.addAndGet(1);return connection.borrowConnection();} catch (ClassNotFoundException ex){LOG.error("class {} not found", this.smpConfig.getDriverClassName(), ex);throw new SQLException(ex);}finally {if (locked){GET_CONNECTION_LOCK.unlock();}}}private SmpConnectionProxy createConnection() throws ClassNotFoundException, SQLException {Class.forName( this.smpConfig.getDriverClassName() );Connection connection = DriverManager.getConnection( this.smpConfig.getUrl(), this.smpConfig.getUsername(), this.smpConfig.getPassword());LOG.debug("create new database connection with url:{}", this.smpConfig.getUrl());return new SmpConnectionProxy(connection, this, connection.getAutoCommit());}

4:構建spring-boot-starter

? ? ? ? ?這里需要說明的是springboot默認會嘗試使用com.zaxxer.hikari.HikariDataSource，org.apache.tomcat.jdbc.pool.DataSource，org.apache.commons.dbcp2.BasicDataSource作為連接池，相關代碼邏輯在org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration，因此配置spring-boot-starter的時候先要確保應用沒有配置連接池。

核心代碼:

?5:springboot使用

添加依賴后再添加如下配置:

spring.datasource.type=com.lauor.smpdb.SmpDataSource #最小連接數,默認4 spring.datasource.smpdb.minIdle=4 #最大連接數，默認40 spring.datasource.smpdb.maxActive=20 #數據庫連接有效期檢查間隔時間ms,默認30分鐘，最小1s spring.datasource.smpdb.keepaliveTimeInMill=1800000 #獲取數據庫連接最大等待時間ms,默認30s,最小1s spring.datasource.smpdb.maxWaitInMill=30000 #數據連接合法性校驗超時時間,默認5s,最小1s spring.datasource.smpdb.validationTimeoutInMill=5000

連接池完整代碼:https://gitee.com/tandatda/smpdb

連接池使用完整demo:https://gitee.com/tandatda/demo-edr-smpdb

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