多线程-数据库连接池模拟实现

1

package com.mrtang.studstar.test;

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


public class ConnectionDriver {
    static class ConnectionHandler implements InvocationHandler {
        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的代理，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());
    }
}

package com.mrtang.studstar.test;

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

public class ConnectionPool {
    private LinkedList<Connection> pool = new LinkedList<Connection>();
    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经归还了一个连接
                pool.addLast(connection); pool.notifyAll();
            }
        }
    }// 在mills内无法获取到连接，将会返回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;
            }
        }
    }
}

package com.mrtang.studstar.test;

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

public class ConnectionPoolTest {
    static ConnectionPool pool = new ConnectionPool(10); // 保证所有ConnectionRunner能够同时开始
    static CountDownLatch start = new CountDownLatch(1); // main线程将会等待所有ConnectionRunner结束后才能继续执行
    static CountDownLatch end;
    public static void main(String[] args) throws Exception {
        // 线程数量，可以修改线程数量进行观察
        int threadCount = 50;
        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), "ConnectionRunnerThread");
            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;
        }
        public void run() {
            try {
                start.await();
            } catch (Exception ex) {

            }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 ex) {

            } finally {
                count--;
            }
            }end.countDown();
        }
    }
}