起因

bonecp不具備回縮功能，即連接池持有連接之後，不會主動去釋放這些連接（即使這些連接始終處於空閑狀態），因此在使用一段時間之後，連接池會達到配置的最大值。

這種方式一定程度上造成了資源的浪費。

改造

參考tomcat-jdbc的策略，每隔一段時間（可配置）會啟動定時任務掃描partition中的idle隊列，判斷idle連接數是否大於partition可持有的最小連接數，如果是，則啟動清理方法，將連接釋放掉。

為了達到這個目的，實現了ConnectionCleanThread類：

package com.jolbox.bonecp;

import java.sql.SQLException;
import java.util.concurrent.BlockingQueue;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ConnectionCleanThread implements Runnable {

    private static final Logger logger = LoggerFactory.getLogger(ConnectionCleanThread.class);
    
    private ConnectionPartition partition;
    
    private BoneCP pool;
    
    protected ConnectionCleanThread(ConnectionPartition connectionPartition, BoneCP pool) {
        this.partition = connectionPartition;
        this.pool = pool;
    }
    
    @Override
    public void run() {
        BlockingQueue freeQueue = null;
        ConnectionHandle connection = null;
        //獲得partition的大小
        int partitionSize = this.partition.getAvailableConnections();
        for (int i = 0; i < partitionSize; i++) {
            //得到free連接的queue
            freeQueue = this.partition.getFreeConnections();
            //如果空閑連接大於partition的最小允許連接數,回縮到最小允許連接數
            while (freeQueue.size() > this.partition.getMinConnections()) {
                connection = freeQueue.poll();
                connection.lock();
                closeConnection(connection);
                connection.unlock();
            }
        }
    }
    
    /** Closes off this connection
     * @param connection to close
     */
    private void closeConnection(ConnectionHandle connection) {

        if (connection != null && !connection.isClosed()) {
            try {
                connection.internalClose();
            } catch (SQLException e) {
                logger.error("Destroy connection exception", e);
            } finally {
                this.pool.postDestroyConnection(connection);
                connection.getOriginatingPartition().getPoolWatchThreadSignalQueue().offer(new Object()); // item being pushed is not important.
            }
        }
    }

}

同時需要對核心類ConnectionHandle進行改造，加上連接的上鎖方法：

protected void lock() {
    lock.writeLock().lock();
}
    
protected void unlock() {
    lock.writeLock().unlock();
}

在BoneCP類的構造器內加上該線程的定時任務：

/**
 * 空閑連接清理任務
*/
private ScheduledExecutorService connectionCleanScheduler;

...

this.connectionCleanScheduler = Executors.newScheduledThreadPool(this.config.getPartitionCount(), new CustomThreadFactory("BoneCP-connection-clean-thread"+suffix, true));

...

//定期啟動一個線程清理空閑連接
//add 2017-2-10
final Runnable connectionCleaner = new ConnectionCleanThread(connectionPartition, this);
this.connectionCleanScheduler.scheduleAtFixedRate(connectionCleaner, this.config.getConnectionCleanTimeInSeconds(), this.config.getConnectionCleanTimeInSeconds(), TimeUnit.SECONDS);

效果

經過實際測試，可以在後臺自動的回收idle連接。

現在只是實現了功能，各種情況暫時沒有加入考慮，比如沒有判斷該連接是否應該被釋放。

GitHub地址

bonecp