/**
 *  Title  pams
 *  @author: dzc
 *  Company: hust
 *  @version 1.0
 *  Date  :   2006-04
 *  DBConnectionManager.java
 **/

package pams.database;

import java.io.*;
import java.sql.*;
import java.util.*;
import java.util.Date;

public class DBConnectionManager {
	static private DBConnectionManager instance; // 唯一實(shí)例

	static private int clients;

	private Vector drivers = new Vector();

	private Hashtable pools = new Hashtable();

	/**
	 * 將文本信息在后臺(tái)打印出來
	 */
	private void log(String msg) {
		 System.out.println(new Date() + ": " + msg);
	}

	/**
	 * 返回唯一實(shí)例.如果是第一次調(diào)用此方法,則創(chuàng)建實(shí)例
	 * 
	 * @return DBConnectionManager 唯一實(shí)例
	 */
	static synchronized public DBConnectionManager getInstance() {
		if (instance == null) {
			instance = new DBConnectionManager();
		}
		clients++;
		return instance;
	}

	/**
	 * 建構(gòu)函數(shù)私有以防止其它對(duì)象創(chuàng)建本類實(shí)例
	 */
	private DBConnectionManager() {
		init();
	}

	/**
	 * 將連接對(duì)象返回給由名字指定的連接池
	 * 
	 * @param name
	 *            在屬性文件中定義的連接池名字
	 * @param con
	 *            連接對(duì)象
	 */
	public void freeConnection(String name, Connection con) {
		DBConnectionPool pool = (DBConnectionPool) pools.get(name);
		if (pool != null) {
			pool.freeConnection(con);
		}
	}

	/**
	 * 獲得一個(gè)可用的(空閑的)連接.如果沒有可用連接,且已有連接數(shù)小于最大連接數(shù) 限制,則創(chuàng)建并返回新連接
	 * 
	 * @param name
	 *            在屬性文件中定義的連接池名字
	 * @return Connection 可用連接或null
	 */
	public Connection getConnection(String name) {
		DBConnectionPool pool = (DBConnectionPool) pools.get(name);
		if (pool != null) {
			return pool.getConnection();
		}
		return null;
	}

	/**
	 * 獲得一個(gè)可用連接.若沒有可用連接,且已有連接數(shù)小于最大連接數(shù)限制, 則創(chuàng)建并返回新連接.否則,在指定的時(shí)間內(nèi)等待其它線程釋放連接.
	 * 
	 * @param name
	 *            連接池名字
	 * @param time
	 *            以毫秒計(jì)的等待時(shí)間
	 * @return Connection 可用連接或null
	 */
	public Connection getConnection(String name, long time) {
		DBConnectionPool pool = (DBConnectionPool) pools.get(name);
		if (pool != null) {
			return pool.getConnection(time);
		}
		return null;
	}

	/**
	 * 關(guān)閉所有連接,撤銷驅(qū)動(dòng)程序的注冊(cè)
	 */
	public synchronized void release() {
		// 等待直到最后一個(gè)客戶程序調(diào)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("撤銷JDBC驅(qū)動(dòng)程序 " + driver.getClass().getName() + "的注冊(cè)");
			} catch (SQLException e) {
				log("無法撤銷下列JDBC驅(qū)動(dòng)程序的注冊(cè): " + driver.getClass().getName());
			}
		}
	}

	/**
	 * 根據(jù)指定屬性創(chuàng)建連接池實(shí)例.
	 * 
	 * @param props
	 *            連接池屬性
	 */
	private void createPools(Properties props) {
		Enumeration propNames = props.propertyNames();
		while (propNames.hasMoreElements()) {
			String name = (String) propNames.nextElement();
			if (name.endsWith(".url")) 
			{
				String poolName = "sqlserver";
				String url = props.getProperty(poolName + ".url");
				if (url == null) 
				{
					log("沒有為連接池" + 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("錯(cuò)誤的最大連接數(shù)限制: " + maxconn + " .連接池: " + poolName);
					max = 0;
				}
				DBConnectionPool pool = new DBConnectionPool(poolName, url,
						user, password, max);
				pools.put(poolName, pool);
				log("成功創(chuàng)建連接池" + poolName);
			}
		}
	}

	/**
	 * 讀取屬性完成初始化
	 */
	private void init() {
		InputStream is = getClass().getResourceAsStream("/pams.txt");
		Properties dbProps = new Properties();
		try {
			dbProps.load(is);
		} catch (Exception e) {
			log("不能讀取屬性文件.請(qǐng)確保db.properties在CLASSPATH指定的路徑中");
			return;
		}
		loadDrivers(dbProps);
		createPools(dbProps);
	}

	/**
	 * 裝載和注冊(cè)所有JDBC驅(qū)動(dòng)程序
	 * 
	 * @param props
	 *            屬性
	 */
	private void loadDrivers(Properties props) {
		String driverClasses = props.getProperty("driver");
		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("成功注冊(cè)JDBC驅(qū)動(dòng)程序" + driverClassName);
			} catch (Exception e) {
				log("無法注冊(cè)JDBC驅(qū)動(dòng)程序: " + driverClassName + ", 錯(cuò)誤: " + e);
			}
		}
	}

	
	/**
	 * 此內(nèi)部類定義了一個(gè)連接池.它能夠根據(jù)要求創(chuàng)建新連接,直到預(yù)定的最大連接數(shù)為止.在返回連接給客戶程序之前,它能夠驗(yàn)證連接的有效性.
	 */
	class DBConnectionPool {
		private int userCount;

		private Vector freeConnections = new Vector();

		private int maxConn;

		private String name;

		private String password;

		private String URL;

		private String user;

//		private String databaseUrl;

		/**
		 * 創(chuàng)建新的連接池
		 * 
		 * @param name
		 *            連接池名字
		 * @param URL
		 *            數(shù)據(jù)庫的JDBC URL
		 * @param user
		 *            數(shù)據(jù)庫帳號(hào),或 null
		 * @param password
		 *            密碼,或 null
		 * @param maxConn
		 *            此連接池允許建立的最大連接數(shù)
		 */
		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;
		}

		/**
		 * 將不再使用的連接返回給連接池
		 * 
		 * @param con
		 *            客戶程序釋放的連接
		 */
		public synchronized void freeConnection(Connection con) {
			// 將指定連接加入到向量末尾
			freeConnections.addElement(con);
			userCount--;
			notifyAll();
		}

		/**
		 * 從連接池獲得一個(gè)可用連接.如沒有空閑的連接且當(dāng)前連接數(shù)小于最大連接 數(shù)限制,則創(chuàng)建新連接.如原來登記為可用的連接不再有效,則從向量刪除之,
		 * 然后遞歸調(diào)用自己以嘗試新的可用連接.
		 */
		public synchronized Connection getConnection() {
			Connection con = null;
			if (freeConnections.size() > 0) {
				// 獲取向量中第一個(gè)可用連接
				con = (Connection) freeConnections.firstElement();
				freeConnections.removeElementAt(0);
				try {
					if (con.isClosed()) {
						log("從連接池" + name + "刪除一個(gè)無效連接");
						// 遞歸調(diào)用自己,嘗試再次獲取可用連接
						con = getConnection();
					}
				} catch (SQLException e) {
					log("從連接池" + name + "刪除一個(gè)無效連接");
					// 遞歸調(diào)用自己,嘗試再次獲取可用連接
					con = getConnection();
				}
			} else if (maxConn == 0 || userCount < maxConn) {
				con = newConnection();
			}
			if (con != null) {
				userCount++;
			}
			return con;
		}

		/**
		 * 從連接池獲取可用連接.可以指定客戶程序能夠等待的最長(zhǎng)時(shí)間 參見前一個(gè)getConnection()方法.
		 * 
		 * @param timeout
		 *            以毫秒計(jì)的等待時(shí)間限制
		 */
		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()返回的原因是超時(shí)
					return null;
				}
			}
			return con;
		}

		/**
		 * 關(guān)閉所有連接
		 */
		public synchronized void release() {
			Enumeration allConnections = freeConnections.elements();
			while (allConnections.hasMoreElements()) {
				Connection con = (Connection) allConnections.nextElement();
				try {
					con.close();
					log("關(guān)閉連接池" + name + "中的一個(gè)連接");
				} catch (SQLException e) {
					log("無法關(guān)閉連接池" + name + "中的連接");
				}
			}
			freeConnections.removeAllElements();
		}

		/**
		 * 創(chuàng)建新的連接
		 */
		private Connection newConnection() {
			Connection con = null;
			try {
				if (user == null) {
					con = DriverManager.getConnection(URL);
				} else {
					con = DriverManager.getConnection(URL, user, password);
				}
				log("連接池" + name + "創(chuàng)建一個(gè)新的連接");
			} catch (SQLException e) {
				log("無法創(chuàng)建下列URL的連接: " + URL);
				return null;
			}
			return con;
		}

	}
}