简单的数据库连接池实例(java语言)

1.概述

频繁的创建和销毁数据库连接消耗非常多的系统资源，创建一个池子， 管理一定数量的连接，用的时候去池中取，用完了放回池中，这时比较通用的做法。

2.关键字

LinkedList synchronized InvocationHandler CountDownLatch

3. 代码

3.1 ConnectionPool.java

package com.rocky.pool;

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.createConection());
}
}
}

public void releaseConnection(Connection connection){
if(connection != null){
synchronized (pool) {
//连接释放后 要进行通知 这样其他消费者能够感知池中已经归还了一个连接
pool.addLast(connection);
//                pool.notifyAll();//all
pool.notify();//all

}
}
}

public  Connection fetchConnection(long mills) throws InterruptedException{
synchronized (pool) {
//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;
}
}

}
}

3.2 ConnectionDriver.java

package com.rocky.pool;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;

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")){
Thread.sleep(1000);
}
return null;
}
}

//创建一个connection的代理
public static Connection createConection(){
return (Connection) Proxy.newProxyInstance(ConnectionDriver.class.getClassLoader(), new Class<?>[]{Connection.class},new ConnectionHandler());
}
}

3.3 ConnectionPoolTest.java

package com.rocky.pool;

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

public class ConnectionPoolTest {

static ConnectionPool pool = new ConnectionPool(10);

//保证所有runner能够同时运行
static CountDownLatch start = new CountDownLatch(1);

static CountDownLatch end ;

public static void main(String[] args) throws Exception {
int threadCount = 20;

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 ConnectionRunner(count, got, notGot), "ConectionRunnerThread"+i);
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 ConnectionRunner implements Runnable{

int count ;
AtomicInteger got;
AtomicInteger notGot;
public ConnectionRunner(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) {
e.printStackTrace();
}
while(count > 0){
try {
Connection connection = pool.fetchConnection(1000);
if(connection != null){
try{
connection.createStatement();
connection.commit();
}finally{
pool.releaseConnection(connection);
got.incrementAndGet();
}
}else{
notGot.incrementAndGet();
}
} catch (InterruptedException | SQLException e) {
e.printStackTrace();
}finally{
count--;
}
}
end.countDown();
}

}

}

3.4 说明

通过改变main方法中的threadCount的数量可以观察 随着线程数的增加 获取连接命中的比例在下降，

这时因为连接池中的连接数一定(10个) 而客户端线程会等待并超时返回。