tomcat jdbc连接池详解之初始化

小鱼儿 2021-10-15 04:45 373阅读 0赞

本文将从源码出发详解tomcat jdbc连接池的初始化过程，看下连接池初始化到底做了些什么

//创建连接池
         public ConnectionPool(PoolConfiguration prop) throws SQLException {
            //初始化连接池
            init(prop);
        }
    
    
            protected void init(PoolConfiguration properties) throws SQLException {
            poolProperties = properties;
    
            //校验连接池配置参数
            checkPoolConfiguration(properties);
    
            //make space for 10 extra in case we flow over a bit
            busy = new LinkedBlockingQueue<>();
            //busy = new FairBlockingQueue<PooledConnection>();
            //make space for 10 extra in case we flow over a bit
            if (properties.isFairQueue()) {
                idle = new FairBlockingQueue<>();
                //idle = new MultiLockFairBlockingQueue<PooledConnection>();
                //idle = new LinkedTransferQueue<PooledConnection>();
                //idle = new ArrayBlockingQueue<PooledConnection>(properties.getMaxActive(),false);
            } else {
                idle = new LinkedBlockingQueue<>();
            }
    
            //初始化PoolCleaner，该类是一个TimerTask，在定期任务内会执行checkAbandoned、checkIdle、testAllIdle等任务，详情可以参考https://mp.csdn.net/postedit/99671525
            initializePoolCleaner(properties);
    
            //create JMX MBean
            if (this.getPoolProperties().isJmxEnabled()) createMBean();
    
            //Parse and create an initial set of interceptors. Letting them know the pool has started.
            //These interceptors will not get any connection.
            PoolProperties.InterceptorDefinition[] proxies = getPoolProperties().getJdbcInterceptorsAsArray();
            for (int i=0; i<proxies.length; i++) {
                try {
                    if (log.isDebugEnabled()) {
                        log.debug("Creating interceptor instance of class:"+proxies[i].getInterceptorClass());
                    }
                    JdbcInterceptor interceptor = proxies[i].getInterceptorClass().newInstance();
                    interceptor.setProperties(proxies[i].getProperties());
                    interceptor.poolStarted(this);
                }catch (Exception x) {
                    log.error("Unable to inform interceptor of pool start.",x);
                    if (jmxPool!=null) jmxPool.notify(org.apache.tomcat.jdbc.pool.jmx.ConnectionPool.NOTIFY_INIT, getStackTrace(x));
                    close(true);
                    SQLException ex = new SQLException();
                    ex.initCause(x);
                    throw ex;
                }
            }
    
            //用initialSize初始化线程池
            PooledConnection[] initialPool = new PooledConnection[poolProperties.getInitialSize()];
            try {
                for (int i = 0; i < initialPool.length; i++) {
                    //创建连接，创建的连接会被加入到busy队列
                    initialPool[i] = this.borrowConnection(0, null, null); //don't wait, should be no contention
                } //for
    
            } catch (SQLException x) {
                log.error("Unable to create initial connections of pool.", x);
                if (!poolProperties.isIgnoreExceptionOnPreLoad()) {
                    if (jmxPool!=null) jmxPool.notify(org.apache.tomcat.jdbc.pool.jmx.ConnectionPool.NOTIFY_INIT, getStackTrace(x));
                    close(true);
                    throw x;
                }
            } finally {
                //返回创建的初始化连接到idle队列中
                for (int i = 0; i < initialPool.length; i++) {
                    if (initialPool[i] != null) {
                        try {this.returnConnection(initialPool[i]);}catch(Exception x){/*NOOP*/}
                    } //end if
                } //for
            } //catch
    
            closed = false;
        }

如上述代码所示tomcat jdbc连接池初始化做了以下工作：

1.检查连接池配置属性

2.初始化连接池任务（创建PoolCleaner）

3、根据initialSize创建PoolConnection数组，然后放入到idle队列中，这样从连接池获取数据库连接的时候就可以先使用idle队列中连接，如果idle连接没有可用连接则会判断当前连接池大小是否超过连接池配置的maxActive，如果没有则创建新的数据库连接，否则就会阻塞等待获取到连接为止（当前不是无条件等待，会有一个超时时间-根据连接池maxWait来定）！