我们创建三个类：SqlConnectImpl、DBPoolSemaphore 、Test
/**
*类说明：数据库连接的简单实现，这里只实现fetchConnection（）方法
*/
public class SqlConnectImpl implements Connection{
/*拿一个数据库连接*/
public static final Connection fetchConnection(){
return new SqlConnectImpl();
}
//后面还有许多要实现的方法，这里我们只用这一个方法，领悟精神..就不co下来了
}/**
*类说明：演示Semaphore用法，一个数据库连接池的实现
*/
public class DBPoolSemaphore {
private final static int POOL_SIZE = 10;
private final Semaphore useful,useless;//useful表示可用的数据库连接，useless表示已用的数据库连接
public DBPoolSemaphore() {
this. useful = new Semaphore(POOL_SIZE);
this.useless = new Semaphore(0);
}
//存放数据库连接的容器
private static LinkedList<Connection> pool = new LinkedList<Connection>();
//初始化池.
static {
for (int i = 0; i < POOL_SIZE; i++) {
pool.addLast(SqlConnectImpl.fetchConnection());
}
}
/*归还连接*/
public void returnConnect(Connection connection) throws InterruptedException {
if(connection!=null) {
System.out.println("当前有"+useful.getQueueLength()+"个线程等待数据库连接！！"
+"可用连接数:"+useful.availablePermits());
useless.acquire();
synchronized (pool) {
pool.addLast(connection);
}
useful.release();
}
}
/*从池子拿连接*/
public Connection takeConnect() throws InterruptedException {
//拿连接，如果拿不到连接，那么线程会被阻塞在此
useful.acquire();
Connection conn;
synchronized (pool) {
conn = pool.removeFirst();
}
useless.release();
return conn;
}
}
/**
*测试数据库连接池
*/
public class Test {
private static final DBPoolSemaphore dbPool = new DBPoolSemaphore();
//业务线程
private static class BusiThread extends Thread{
@Override
public void run() {
Random r = new Random();//让每个线程持有连接的时间不一样
long start = System.currentTimeMillis();
try {
Connection connect = dbPool.takeConnect();
System.out.println("Thread_"+Thread.currentThread().getId()
+"_获取数据库连接共耗时【"+(System.currentTimeMillis()-start)+"】ms.");
SleepTools.ms(100+r.nextInt(100));//模拟业务操作，线程持有连接查询数据
System.out.println("查询数据完成，归还连接！");
dbPool.returnConnect(connect);
} catch (InterruptedException e) {
}
}
}
public static void main(String[] args) {
for (int i = 0; i < 50; i++) {
Thread thread = new BusiThread();
thread.start();
}
}
}
这里我们创建了50个线程，模仿用户获取连接，打引如下，可自行拿代码尝试
