java 数据库连接池的实现代码

package com.xiaobian;

/**
 * 数据库连接池管理类
 */
import java.io.*;
import java.sql.*;
import java.util.*;
import java.util.Date;

/**
 * 管理类DBConnectionManager支持对一个或多个由属性文件定义的数据库连接池的
 * 访问.客户程序可以调用getInstance()方法访问本类的唯一实例
 */
public class DBConnectionManager {
	
	public static void main(String[] args) {
		DBConnectionManager connectionManager = DBConnectionManager.getInstance();
		
		Connection conn =  connectionManager.getConnection("idb");
			try {
				Thread.sleep(10);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		Connection conn1 =  connectionManager.getConnection("idb");
		Connection conn2 =  connectionManager.getConnection("idb");
		Connection conn3 =  connectionManager.getConnection("idb");
		Connection conn4 =  connectionManager.getConnection("idb");
		Connection conn5 =  connectionManager.getConnection("idb");
		connectionManager.freeConnection("idb", conn);
		connectionManager.freeConnection("idb", conn1);
		connectionManager.freeConnection("idb", conn2);
		connectionManager.freeConnection("idb", conn3);
		connectionManager.freeConnection("idb", conn4);
		connectionManager.freeConnection("idb", conn5);
		Connection conn6 = connectionManager.getConnection("idb");
		Connection conn7 = connectionManager.getConnection("idb");
		System.out.println(" conn6 == "+conn6 +" conn7 == "+conn7);
		
	}

	
	static private DBConnectionManager instance; // 唯一实例

	static private int clients; //

	private Vector drivers = new Vector();

	private PrintWriter log;

	private Hashtable pools = new Hashtable();

	/**
	 * 返回唯一实例.如果是第一次调用此方法,则创建实例
	 * 
	 * @return DBConnectionManager 唯一实例
	 */
	static synchronized public DBConnectionManager getInstance() {
		if (instance == null) {
			instance = new DBConnectionManager();
		}
		clients++;
		return instance;
	}

	/**
	 * 建构私有函数以防止其它对象创建本类实例
	 */
	private DBConnectionManager() {
		init();
	}

	/**
	 * 将连接对象返回给由名字指定的连接池
	 * 
	 * @param name
	 *            在属性文件中定义的连接池名字
	 * @param con
	 *            连接对象
	 */
	public void freeConnection(String name, Connection con) {
		DBConnectionPool pool = (DBConnectionPool) pools.get(name);
		if (pool != null) {
			pool.freeConnection(con);
		}
	}

	/**
	 * 获得一个可用的(空闲的)连接.如果没有可用连接,且已有连接数小于最大连接数 限制,则创建并返回新连接
	 * 
	 * @param name
	 *            在属性文件中定义的连接池名字
	 * @return Connection 可用连接或null
	 */
	public Connection getConnection(String name) {
		DBConnectionPool pool = (DBConnectionPool) pools.get(name);
		//System.out.println(" pool == "+pool);
		if (pool != null) {
			return pool.getConnection();
		}
		return null;
	}

	/**
	 * 获得一个可用连接.若没有可用连接,且已有连接数小于最大连接数限制, 则创建并返回新连接.否则,在指定的时间内等待其它线程释放连接.
	 * 
	 * @param name
	 *            连接池名字
	 * @param time
	 *            以毫秒计的等待时间
	 * @return Connection 可用连接或null
	 */
	public Connection getConnection(String name, long time) {
		DBConnectionPool pool = (DBConnectionPool) pools.get(name);
		if (pool != null) {
			return pool.getConnection(time);
		}
		return null;
	}

	/**
	 * 关闭所有连接,撤销驱动程序的注册
	 */
	public synchronized void release() {
		// 等待直到最后一个客户程序调用
		if (--clients != 0) {
			return;
		}
		Enumeration allPools = pools.elements();
		while (allPools.hasMoreElements()) {
			DBConnectionPool pool = (DBConnectionPool) allPools.nextElement();
			pool.release();
		}
		Enumeration allDrivers = drivers.elements();
		while (allDrivers.hasMoreElements()) {
			Driver driver = (Driver) allDrivers.nextElement();
			try {
				DriverManager.deregisterDriver(driver);
				log("撤销JDBC驱动程序 " + driver.getClass().getName() + "的注册");
			} catch (SQLException e) {
				log(e, "无法撤销下列JDBC驱动程序的注册: " + driver.getClass().getName());
			}
		}
	}

	/**
	 * 根据指定属性创建连接池实例.
	 * 
	 * @param props
	 *            连接池属性
	 */
	private void createPools(Properties props) {
		Enumeration propNames = props.propertyNames();
		while (propNames.hasMoreElements()) {
			String name = (String) propNames.nextElement();
			if (name.endsWith(".url")) {
				String poolName = name.substring(0, name.lastIndexOf("."));
				//System.out.println(" poolName ||"+poolName+"|");
				String url = props.getProperty(poolName + ".url");
				if (url == null) {
					log("没有为连接池" + poolName + "指定URL");
					continue;
				}
				String user = props.getProperty(poolName + ".user");
				String password = props.getProperty(poolName + ".password");
				String maxconn = props.getProperty(poolName + ".maxconn", "0");
				int max;
				try {
					max = Integer.valueOf(maxconn).intValue();
				} catch (NumberFormatException e) {
					log("错误的最大连接数限制: " + maxconn + " .连接池: " + poolName);
					max = 0;
				}
				DBConnectionPool pool = new DBConnectionPool(poolName, url,
						user, password, max);
				pools.put(poolName, pool);
				log("成功创建连接池" + poolName);
			}
		}
	}

	// --------------------------------------------------------------------------------

	/**
	 * 读取属性完成初始化
	 */
	private void init() {
		
		InputStream fileinputstream = null;
		try {
			fileinputstream = new FileInputStream("./src/db.properties");
		} catch (FileNotFoundException e1) {
			e1.printStackTrace();
		}
		//BufferedReader bufferedreader = new BufferedReader(new InputStreamReader(fileinputstream));

		//InputStream is = getClass().getResourceAsStream("D:/workspace/UmessageSms/src/db.properties");
		Properties dbProps = new Properties();
		try {
			dbProps.load(fileinputstream);
		} catch (Exception e) {
			e.printStackTrace();
			System.err.println("不能读取属性文件. "
					+ "请确保db.properties在CLASSPATH指定的路径中");
			return;
		}
		String logFile = dbProps.getProperty("logfile",
				"DBConnectionManager.log");
		
		//System.out.println(dbProps.getProperty("logfile"));
		try {
			log = new PrintWriter(new FileWriter(logFile, true), true);
		} catch (IOException e) {
			System.err.println("无法打开日志文件: " + logFile);
			log = new PrintWriter(System.err);
		}
		loadDrivers(dbProps);
		createPools(dbProps);
	}

	/**
	 * 装载和注册所有JDBC驱动程序
	 * 
	 * @param props
	 *            属性
	 */
	private void loadDrivers(Properties props) {
		String driverClasses = props.getProperty("drivers");
		StringTokenizer st = new StringTokenizer(driverClasses);
		while (st.hasMoreElements()) {
			String driverClassName = st.nextToken().trim();
			try {
				Driver driver = (Driver) Class.forName(driverClassName)
						.newInstance();
				DriverManager.registerDriver(driver);
				drivers.addElement(driver);
				log("成功注册JDBC驱动程序" + driverClassName);
			} catch (Exception e) {
				log("无法注册JDBC驱动程序: " + driverClassName + ", 错误: " + e);
			}
		}
	}

	/**
	 * 将文本信息写入日志文件
	 */
	private void log(String msg) {
		log.println(new Date() + ": " + msg);
	}

	/**
	 * 将文本信息与异常写入日志文件
	 */
	private void log(Throwable e, String msg) {
		log.println(new Date() + ": " + msg);
		e.printStackTrace(log);
	}

	/** ************************************************************* */
	/** ********************内部类DBConnectionPool******************** */
	/** ************************************************************* */
	/**
	 * 此内部类定义了一个连接池.它能够根据要求创建新连接,直到预定的最 大连接数为止.在返回连接给客户程序之前,它能够验证连接的有效性.
	 */
	class DBConnectionPool {
		private int checkedOut; // 当前连接数

		private Vector freeConnections = new Vector(); // 保存所有可用连接

		private int maxConn; // 此连接池允许建立的最大连接数

		private String name; // 连接池名字

		private String password; // 密码或null

		private String URL; // 数据库的JDBC URL

		private String user; // 数据库账号或null

		/**
		 * 创建新的连接池
		 * 
		 * @param name
		 *            连接池名字
		 * @param URL
		 *            数据库的JDBC URL
		 * @param user
		 *            数据库帐号或 null
		 * @param password
		 *            密码或 null
		 * @param maxConn
		 *            此连接池允许建立的最大连接数
		 */
		public DBConnectionPool(String name, String URL, String user,
				String password, int maxConn) {
			this.name = name;
			this.URL = URL;
			this.user = user;
			this.password = password;
			this.maxConn = maxConn;
		}

		/**
		 * 将不再使用的连接返回给连接池
		 * 
		 * @param con
		 *            客户程序释放的连接
		 */
		public synchronized void freeConnection(Connection con) {
			// 将指定连接加入到向量末尾
			freeConnections.addElement(con);
			checkedOut--;
			notifyAll(); // 删除等待队列中的所有线程
		}

		/**
		 * 从连接池获得一个可用连接.如果没有空闲的连接且当前连接数小于最大连接
		 * 数限制,则创建新连接.如原来登记为可用的连接不再有效,则从向量删除之, 然后递归调用自己以尝试新的可用连接.
		 */
		public synchronized Connection getConnection() {
			Connection con = null;
			//System.out.println(" freeConnections.size() "+freeConnections.size());
			if (freeConnections.size() > 0) {
				// 获取向量中第一个可用连接
				con = (Connection) freeConnections.firstElement();
				freeConnections.removeElementAt(0);
				try {
					if (con.isClosed()) {
						log("从连接池" + name + "删除一个无效连接");
						// 递归调用自己,尝试再次获取可用连接
						con = getConnection();
					}
				} catch (SQLException e) {
					log("从连接池" + name + "删除一个无效连接");
					// 递归调用自己,尝试再次获取可用连接
					con = getConnection();
				}
			} else if (maxConn == 0 || checkedOut < maxConn) {
				con = newConnection();
			}
			if (con != null) {
				checkedOut++;
			}
			System.out.println("con == "+con);
			return con;
		}

		/**
		 * 从连接池获取可用连接.可以指定客户程序能够等待的最长时间 参见前一个getConnection()方法.
		 * 
		 * @param timeout
		 *            以毫秒计的等待时间限制
		 */
		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) {
					// wait()返回的原因是超时
					return null;
				}
			}
			return con;
		}

		/**
		 * 关闭所有连接
		 */
		public synchronized void release() {
			Enumeration allConnections = freeConnections.elements();
			while (allConnections.hasMoreElements()) {
				Connection con = (Connection) allConnections.nextElement();
				try {
					con.close();
					log("关闭连接池" + name + "中的一个连接");
				} catch (SQLException e) {
					log(e, "无法关闭连接池" + name + "中的连接");
				}
			}
			freeConnections.removeAllElements();
		}

		/**
		 * 创建新的连接
		 */
		private Connection newConnection() {
			Connection con = null;
			try {
				if (user == null) {
					con = DriverManager.getConnection(URL);
				} else {
					con = DriverManager.getConnection(URL, user, password);
				}
				log("连接池" + name + "创建一个新的连接");
			} catch (SQLException e) {
				log(e, "无法创建下列URL的连接: " + URL);
				return null;
			}
			return con;
		}
	}
}

评论

2 楼 gotosuzhou 2011-12-20  

收到，能把源文件给我发下[e-mail]

1 楼 zjqzxjw 2007-12-25  

老大。资源配置文件也发一下。