数据库连接池怎么实现_java数据库连接池原理

public class ConnectionStack{ 

private final int timeout;//单位：秒
private final int capacity;
private LinkedList<ConnWithTime> list=new LinkedList<>();
//内部类，用来记录Connection的上次使用时间
private class ConnWithTime{ 

private final long time=new Date().getTime();//实例化的时间即为上次归还的时间
private Connection conn;
public ConnWithTime(Connection conn){
this.conn=conn;
}
//当前连接是否已经超时
boolean isTimeout(){
return new Date().getTime()-time>timeout*1000;
}
}
public ConnectionStack(int capacity,int timeout){
this.capacity=capacity;
this.timeout=timeout;
}
public synchronized void push(Connection conn){
clearTimeoutConnection();
if(list.size()<capacity){
list.addFirst(new ConnWithTime(conn));
}else{
connection.close();
}
}
private void clearTimeoutConnection(){
//接下来从栈底部开始遍历，把所有超时的连接关闭并且丢弃，直到未超时的连接为止
//ps:在正常情况下，栈底部最后一个也是活跃的，所以直接break了，平常调用应该是常数时间
Iterator<ConnWithTime> iterator = list.descendingIterator();
while (iterator.hasNext()) {
ConnWithTime connWithTime = iterator.next();
if (connWithTime.isTimeout()) {
connWithTime.conn.close();
iterator.remove();
} else {
break;
}
}
}
public synchronized Connection pop(){
if(list.isEmpty())return null;
return list.removeFirst().conn;
}
public synchronized void close(){
Iterator<ConnWithTime> iterator = list.descendingIterator();
while (iterator.hasNext()) {
ConnWithTime connWithTime = iterator.next();
connWithTime.conn.close();
iterator.remove();
}
}

public class DatabasePool{ 

private ConnectionStack stack;
private final String url,username,password;
private volatile boolean isRun=true;
public DatabasePool(String url, String username, String password, int capacity, int timeout) {
this.url = url;
this.username = username;
this.password = password;
stack = new ConnectionStack(capacity, timeout);
}
public Connection getConnection() throws SQLException{
if(!isRun)throw new SQLException("pool closed");
Connection conn=stack.pop();
if(conn==null)conn= DriverManager.getConnection(url, username, password);
final myConn=conn;
//使用动态代理，当调用Connection.close()的时候自动将连接放回连接池中
return (Connection) Proxy.newProxyInstance(
DatabasePool.class.getClassLoader(),
conn.getClass().getInterfaces(),
(proxy, method, args) -> {
if (method.getName().equals("close") && isRun) {
//当为调用close函数并且连接池正在运行，则将连接放入stack中，否则直接调用相关函数
stack.push(myConn);//
} else {
return method.invoke(myConn, args);
}
return null;
});
}
public void close(){
isRun=false;
stack.close();
}
}

DatabasePool pool=new DatabasePool(url,username,password,10,60*60);
//多个线程下可以同时如下使用
Connection conn=null;
try{
conn=pool.getConnection();
...//执行数据库操作 
}catch(SQLException e){
logger.exception(e);
}finally{
if(conn!=null)conn.close();
}