dbconnectionpool.java

一个不错的在线购物管理系统设计分析.有需要的自行下载.

/*
 * Created on 2005-11-15
 * Author 曹汕
 * Version 1.0
 * Copyright by CS.SSPKU Inc. All rights reserved. 
 */
package com.struts.utils;

import java.sql.*;
import java.util.Enumeration;
import java.util.Vector;
import org.apache.commons.logging.*;

/**
 * @author cs
 * 
 * TODO To change the template for this generated type comment go to Window -
 * Preferences - Java - Code Style - Code Templates
 */
public class DBConnectionPool {
	
	private String password;
	private String URL;
	private String user;
	private int maxConn;
	private int checkedOut;
	private Vector freeConnections=new Vector();
	private Log log=LogFactory.getLog(this.getClass().getName());

	//构造函数取得上述的所有参数：
	public DBConnectionPool( String URL, String user,String password, int maxConn) {
		this.URL = URL;
		this.user = user;
		this.password = password;
		this.maxConn = maxConn;

	}
	/**
	 * 获取数据库连接 
	 */
	public synchronized Connection getConnection() { 
		Connection con = null; 
		//存在空闲连接，则从空闲的连接中获取
		if (freeConnections.size() > 0) { 
			//Pick the first Connection in the Vector to get round-robin usage 
			con = (Connection) freeConnections.firstElement(); 
			freeConnections.removeElementAt(0); 
			try { 
				if (con.isClosed()) { 
					log.info("Removed bad connection from the connection pool" ); 
					//Try again recursively 
					con = getConnection(); 
				} 
			} 
			catch (SQLException e) { 
				log.info("Removed bad connection from the connection pool",e); 
				//Try again recursively 
				con = getConnection(); 
			} 
		} 
		//最大连接数为0或者已使用连接数小于最大连接数，新创建一个连接
		else if (maxConn == 0 || checkedOut < maxConn) { 
			con = newConnection(); 
		} 
		if (con != null) { 
			checkedOut++; 
		} 
		return con; 
	}
	/**
	 * 创建一个数据库连接 
	 */
	private Connection newConnection() { 
		Connection con = null; 
		try { 
			if (user == null) { 
				con = DriverManager.getConnection(URL); 
			} 
			else { 
				con = DriverManager.getConnection(URL, user, password); 
			} 
			log.info("Created a new connection in pool "); 
		} 
		catch (SQLException e) { 
			log.info( "Can not create a new connection for " + URL,e); 
		return null; 
		} 
		return con; 

		} 

//	public synchronized Connection getConnection(long timeout) { 
//
//		long startTime = new Date().getTime(); 
//		Connection con; 
//		while ((con = getConnection()) == null) { 
//			try { 
//			wait(timeout); 
//			} 
//			catch (InterruptedException e) {} 
//			if ((new Date().getTime() - startTime) >= timeout) { 
//			// Timeout has expired 
//			return null; 
//			} 
//		} 
//		return con; 
//		} 
	
	/**
	 * 将空闲的连接放入空闲连接vector中
	 * @param con 
	 */
	public synchronized void freeConnection(Connection con) { 
		// Put the connection at the end of the Vector 
		freeConnections.addElement(con); 
		checkedOut--; 
		notifyAll(); 
	}
	
	/**
	 * 释放连接 
	 */
	public synchronized void release() { 
		Enumeration allConnections = freeConnections.elements(); 
		while (allConnections.hasMoreElements()) { 
			Connection con = (Connection) allConnections.nextElement(); 
			try { 
				con.close(); 
				log.info("Closed connection for pool " ); 
			} 
			catch (SQLException e) { 
				log.info("Can not close connection for pool ",e); 
			} 
		} 
		freeConnections.removeAllElements(); 
	}
//	/**
//	 * 日志记录
//	 * @param e
//	 * @param string
//	 * @throws Exception
//	 */
//	private void log(SQLException e, String log) {
//		 e.printStackTrace();
//		 System.out.println(log);
//	}
//	/**
//	 * @param string
//	 */
//	private void log(String log) {
//		System.out.println(log);		
//	} 

}