java druid 连接池释放 druid连接池满

首先搭建连接池环境，简单：

读取druid.properties配置文件

/**
 * @description:
 * @author: zhengyuhui
 * @date: 2022/4/13 10:01
 */
public class JdbcUtil {
	private static DataSource dataSource;

	public static void initDataSource() {
		Properties properties = new Properties();
		InputStream in = JdbcUtil.class.getClassLoader().getResourceAsStream("druid.properties");
		try {
			properties.load(in);
			dataSource = DruidDataSourceFactory.createDataSource(properties);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public static Connection getDataSource() {
		try {
			Connection connection = dataSource.getConnection();
			return connection;
		} catch (SQLException e) {
			e.printStackTrace();
		}
		try {
			ServerSocket serverSocket = new ServerSocket(6666);
		} catch (IOException e) {
			e.printStackTrace();
		}
		return null;
	}

	public static void release(Connection connection, PreparedStatement preparedStatement) {
		try {
			connection.close();
			preparedStatement.close();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
}

#-------------基本属性--------------------------------
url=jdbc:mysql://192.168.0.1/storemanager?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2B8&useSSL=true
username=root
password=123456
#数据源名，当配置多数据源时可以用于区分。注意，1.0.5版本及更早版本不支持配置该项
#默认"DataSource-" + System.identityHashCode(this)
name=zzs001
#如果不配置druid会根据url自动识别dbType，然后选择相应的driverClassName
driverClassName=com.mysql.cj.jdbc.Driver

#-------------连接池大小相关参数--------------------------------
#初始化时建立物理连接的个数
#默认为0
initialSize=0

#最大连接池数量
#默认为8
maxActive=1

#最小空闲连接数量
#默认为0
minIdle=0

#已过期
#maxIdle

#获取连接时最大等待时间，单位毫秒。
#配置了maxWait之后，缺省启用公平锁，并发效率会有所下降，如果需要可以通过配置useUnfairLock属性为true使用非公平锁。
#默认-1，表示无限等待
maxWait=-1

测试代码

public static void main(String[] args) {
        //实例化DataSource
		JdbcUtil.initDataSource();
        //获取连接
		Connection connection = JdbcUtil.getDataSource();
        //获取连接
		Connection connection2 = JdbcUtil.getDataSource();
	}

源码分析

1、调用DruidDataSourceFactory.createDataSource(properties);创建数据源

最终调用了com.alibaba.druid.pool.DruidDataSourceFactory#config方法来

实例化datasource;

2、实例化datasource后并初始化连接；初始化连接有两种模式，如果配置文件中的init参数为true，则实例化datasource时就会去创建连接

如果init参数不为true，则在获取连接的时候(com.alibaba.druid.pool.DruidDataSource#getConnection())才去创建连接；

value = (String) properties.get(PROP_INIT);
        if ("true".equals(value)) {
            dataSource.init();
        }

注:此代码为com.alibaba.druid.pool.DruidDataSourceFactory#config 方法内部代码段

3、init()方法

public void init() throws SQLException {
        //初始化判断，如果已经初始化了，则直接返回
        if (inited) {
            return;
        }

        // bug fixed for dead lock, for issue #2980
        DruidDriver.getInstance();

        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());

            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);
            }

            if (this.jdbcUrl != null) {
                this.jdbcUrl = this.jdbcUrl.trim();
                initFromWrapDriverUrl();
            }

            for (Filter filter : filters) {
                filter.init(this);
            }

            if (this.dbType == null || this.dbType.length() == 0) {
                this.dbType = JdbcUtils.getDbType(jdbcUrl, null);
            }

            if (JdbcConstants.MYSQL.equals(this.dbType)
                    || JdbcConstants.MARIADB.equals(this.dbType)
                    || JdbcConstants.ALIYUN_ADS.equals(this.dbType)) {
                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");
                }
            }

            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 (this.driverClass != null) {
                this.driverClass = driverClass.trim();
            }

            initFromSPIServiceLoader();

            if (this.driver == null) {
                if (this.driverClass == null || this.driverClass.isEmpty()) {
                    this.driverClass = JdbcUtils.getDriverClassName(this.jdbcUrl);
                }

                if (MockDriver.class.getName().equals(driverClass)) {
                    driver = MockDriver.instance;
                } else {
                    if (jdbcUrl == null && (driverClass == null || driverClass.length() == 0)) {
                        throw new SQLException("url not set");
                    }
                    driver = JdbcUtils.createDriver(driverClassLoader, driverClass);
                }
            } else {
                if (this.driverClass == null) {
                    this.driverClass = driver.getClass().getName();
                }
            }

            initCheck();

            initExceptionSorter();
            initValidConnectionChecker();
            validationQueryCheck();

            if (isUseGlobalDataSourceStat()) {
                dataSourceStat = JdbcDataSourceStat.getGlobal();
                if (dataSourceStat == null) {
                    dataSourceStat = new JdbcDataSourceStat("Global", "Global", this.dbType);
                    JdbcDataSourceStat.setGlobal(dataSourceStat);
                }
                if (dataSourceStat.getDbType() == null) {
                    dataSourceStat.setDbType(this.dbType);
                }
            } else {
                dataSourceStat = new JdbcDataSourceStat(this.name, this.jdbcUrl, this.dbType, this.connectProperties);
            }
            dataSourceStat.setResetStatEnable(this.resetStatEnable);

            connections = new DruidConnectionHolder[maxActive];
            evictConnections = new DruidConnectionHolder[maxActive];
            keepAliveConnections = new DruidConnectionHolder[maxActive];

            SQLException connectError = null;

            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();
                }
            }

            createAndLogThread();
            //创建连接的线程
            createAndStartCreatorThread();
            createAndStartDestroyThread();

            initedLatch.await();
            init = true;

            initedTime = new Date();
            registerMbean();

            if (connectError != null && poolingCount == 0) {
                throw connectError;
            }

            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 {
            //初始化后把标识位置位，避免重复初始化;
            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);
            }
        }
    }

init()方法中160行createAndStartCreatorThread()方法作为创建物理连接入口；128行 connections = new DruidConnectionHolder[maxActive] 初始化连接池；

inited 参数作为全局参数，如果初始化过了，第二次初始化将被拒绝；

4、createAndStartCreatorThread()方法中调用CreateConnectionThread()线程创建连接；核心上代码

public class CreateConnectionThread extends Thread {

        public CreateConnectionThread(String name){
            super(name);
            this.setDaemon(true);
        }

        public void run() {
            initedLatch.countDown();

            long lastDiscardCount = 0;
            int errorCount = 0;
            for (;;) {
                // addLast
                try {
                    lock.lockInterruptibly();
                } catch (InterruptedException e2) {
                    break;
                }

                long discardCount = DruidDataSource.this.discardCount;
                boolean discardChanged = discardCount - lastDiscardCount > 0;
                lastDiscardCount = discardCount;

                try {
                    boolean emptyWait = true;

                    if (createError != null
                            && poolingCount == 0
                            && !discardChanged) {
                        emptyWait = false;
                    }

                    if (emptyWait
                            && asyncInit && createCount < initialSize) {
                        emptyWait = false;
                    }

                    if (emptyWait) {
                        // 必须存在线程等待，才创建连接
                        if (poolingCount >= notEmptyWaitThreadCount //
                                && (!(keepAlive && activeCount + poolingCount < minIdle))
                                && !isFailContinuous()
                        ) {
                            empty.await();
                        }

                        // 防止创建超过maxActive数量的连接
                        if (activeCount + poolingCount >= maxActive) {
                            empty.await();
                            continue;
                        }
                    }

                } catch (InterruptedException e) {
                    lastCreateError = e;
                    lastErrorTimeMillis = System.currentTimeMillis();

                    if (!closing) {
                        LOG.error("create connection Thread Interrupted, url: " + jdbcUrl, e);
                    }
                    break;
                } finally {
                    lock.unlock();
                }

                PhysicalConnectionInfo connection = null;

                try {
                    connection = createPhysicalConnection();
                } catch (SQLException e) {
                    LOG.error("create connection SQLException, url: " + jdbcUrl + ", errorCode " + e.getErrorCode()
                              + ", state " + e.getSQLState(), e);

                    errorCount++;
                    if (errorCount > connectionErrorRetryAttempts && timeBetweenConnectErrorMillis > 0) {
                        // fail over retry attempts
                        setFailContinuous(true);
                        if (failFast) {
                            lock.lock();
                            try {
                                notEmpty.signalAll();
                            } finally {
                                lock.unlock();
                            }
                        }

                        if (breakAfterAcquireFailure) {
                            break;
                        }

                        try {
                            Thread.sleep(timeBetweenConnectErrorMillis);
                        } catch (InterruptedException interruptEx) {
                            break;
                        }
                    }
                } catch (RuntimeException e) {
                    LOG.error("create connection RuntimeException", e);
                    setFailContinuous(true);
                    continue;
                } catch (Error e) {
                    LOG.error("create connection Error", e);
                    setFailContinuous(true);
                    break;
                }

                if (connection == null) {
                    continue;
                }

                boolean result = put(connection);
                if (!result) {
                    JdbcUtils.close(connection.getPhysicalConnection());
                    LOG.info("put physical connection to pool failed.");
                }

                errorCount = 0; // reset errorCount
            }
        }
    }

第70行:connection = createPhysicalConnection(); 创建了物理连接；

第112行:时调用了put(connection);存放到连接池中

5、下面来看具体存放代码

protected boolean put(PhysicalConnectionInfo physicalConnectionInfo) {
        DruidConnectionHolder holder = null;
        try {
            holder = new DruidConnectionHolder(DruidDataSource.this, physicalConnectionInfo);
        } catch (SQLException ex) {
            lock.lock();
            try {
                if (createScheduler != null) {
                    clearCreateTask(physicalConnectionInfo.createTaskId);
                }
            } finally {
                lock.unlock();
            }
            LOG.error("create connection holder error", ex);
            return false;
        }

        return put(holder, physicalConnectionInfo.createTaskId);
    }

在第四行，构建了DruidConnectionHolder对象，并将物理连接的taskId作为值传入put方法

6、存放连接池

private boolean put(DruidConnectionHolder holder, long createTaskId) {
        lock.lock();
        try {
            if (poolingCount >= maxActive) {
                return false;
            }
            connections[poolingCount] = holder;
            incrementPoolingCount();

            if (poolingCount > poolingPeak) {
                poolingPeak = poolingCount;
                poolingPeakTime = System.currentTimeMillis();
            }

            notEmpty.signal();
            notEmptySignalCount++;

            if (createScheduler != null) {
                clearCreateTask(createTaskId);

                if (poolingCount + createTaskCount < notEmptyWaitThreadCount //
                    && activeCount + poolingCount + createTaskCount < maxActive) {
                    emptySignal();
                }
            }
        } finally {
            lock.unlock();
        }
        return true;
    }

第七行   connections[poolingCount] = holder;  将DruidConnectionHolder对象存放到了连接池中;并在第八行调用incrementPoolingCount()方法增加poolingCount加一，以便下次新增连接可以存放；代码如下:

private final void incrementPoolingCount() {
        poolingCount++;
    }

至此，数据连接的初始化，连接创建已完成，并存放到了connections[poolingCount] 数组中