简单的数据库连接池示例

1.连接池创建

package lcc.dxc.DatabaseConnectionPool;

import java.sql.Connection;
import java.util.LinkedList;

/**
 * @Author:
 * @Description: 简易的数据库连接池创建
 * @Date: 
 */
public class ConnectionPool {

    private LinkedList<Connection> pool = new LinkedList<>();

    public ConnectionPool(int initialSize){
        if(initialSize > 0){
            for (int i = 0; i < initialSize ; i++) {
                pool.addLast(ConnectionDriver.createConnection());
            }
        }
    }

    public void releaseConnection(Connection connection){
        if(connection != null){
            synchronized (pool){
                //连接释放后需要进行通知，这样其他消费者能够感知到连接池中已归还了一个连接
                pool.addLast(connection);
                pool.notifyAll();
            }
        }
    }

    //在 mills内无法获取到连接，将返回 null
    public Connection fetchConnection(long mills) throws InterruptedException {
        synchronized (pool){
            //完全超时
            if(mills <= 0){
                while (pool.isEmpty()){
                    pool.wait();
                }
                return pool.removeFirst();
            }else{
                long future = System.currentTimeMillis() + mills;
                long remaining = mills;
                while (pool.isEmpty() && remaining > 0){
                    pool.wait(remaining);
                    remaining = future - System.currentTimeMillis();
                }
                Connection result = null;
                if(!pool.isEmpty()){
                    result = pool.removeFirst();
                }
                return result;
            }
        }
    }
}

 2.由于java.sql.Connection 是一个接口，最终的实现是由数据库驱动提供方来实现的，博主只是为了娱乐，就用动态代理构造了一个Connection,改Connection的代理实现仅仅是在commit()方法调用时休眠100毫秒，如下

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.util.concurrent.TimeUnit;

/**
 * @Author: Lcc
 * @Description: 数据库连接创建
 * @Date: 2019/11/1
 */
public class ConnectionDriver {

    static class ConnectionHandler implements InvocationHandler{

        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if(method.getName().equals("commit")){
                TimeUnit.MILLISECONDS.sleep(100);
            }
            return null;
        }
    }

    //创建一个 Connection 代理，在 commit 时休眠 100 毫秒
    public static final Connection createConnection(){
        return (Connection) Proxy.newProxyInstance(ConnectionDriver.class.getClassLoader(),
                new Class<?>[]{Connection.class}, new ConnectionHandler());
    }
}

3.模拟客户端ConnectionRunner获取、使用、最后释放连接的过程，当他使用时连接将会增加获取到连接的数量，反之，将会增加未获取到连接的数量，如下： 

package lcc.dxc.DatabaseConnectionPool;

import java.sql.Connection;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @Author: Lcc
 * @Description: 数据库线程池的测试
 *
 * @Date: 2019/11/1
 */
public class ConnectionPoolTest {

    static ConnectionPool pool = new ConnectionPool(10);
    //保证所有的ConnectionRunner 能够同时开始
    static CountDownLatch start = new CountDownLatch(1);
    //main 线程将会等待所有 ConnectionRunner 结束才能继续执行
    static CountDownLatch end;

    public static void main(String[] args) throws InterruptedException {
        //线程数量，可以修改线程数量进行观察
        int threadCount = 100;
        end = new CountDownLatch(threadCount);
        int count  = 20;
        AtomicInteger got = new AtomicInteger();
        AtomicInteger notGot = new AtomicInteger();
        for (int i = 0; i < threadCount; i++) {
            Thread thread = new Thread(new ConnetionRunner(count, got, notGot), "ConnetionRunnerThread");
            thread.start();
        }
        start.countDown();
        end.await();
        System.out.println("total invoke:" +(threadCount * count));
        System.out.println(" got connection : " + got);
        System.out.println(" not got connection : " + notGot);
    }


    static class ConnetionRunner implements Runnable{

        int count;
        AtomicInteger got;
        AtomicInteger notGot;

        public ConnetionRunner(int count, AtomicInteger got, AtomicInteger notGot) {
            this.count = count;
            this.got = got;
            this.notGot = notGot;
        }

        @Override
        public void run() {
            try {
                start.await();
            } catch (InterruptedException e) {
            }
            while(count > 0){
                try {
                    //从线程池中获取连接，如果1000ms内无法获取到，将会返回null
                    //分别统计连接获取的数量got和未获取到的数量 notGot
                    Connection connection = pool.fetchConnection(1000);
                    if(connection != null){
                        try{
                            connection.createStatement();
                            connection.commit();
                        }finally {
                            pool.releaseConnection(connection);
                            got.incrementAndGet();
                        }
                    }else {
                        notGot.incrementAndGet();
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }finally {
                    count--;
                }
            }
            end.countDown();
        }
    }
}

 执行结果：

纯属娱乐，不喜勿喷