kyledbconnectionpoolmanager.java

创建中间企业对象层

package com.kyle.eobject;

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 KyleDBConnectionPoolManager
{
	static private KyleDBConnectionPoolManager 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 KyleDBConnectionPoolManager getInstance()
	{
		if (instance == null)
		{
			instance = new KyleDBConnectionPoolManager();
		}
		clients++;
		return instance;
	}

	/**
	* 建构函数私有以防止其它对象创建本类实例
	*/
	private KyleDBConnectionPoolManager()
	{
		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) 
	{
		KyleDBConnectionPool pool = (KyleDBConnectionPool) 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)
	{
		KyleDBConnectionPool pool = (KyleDBConnectionPool) pools.get(name);
		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)
	{
		KyleDBConnectionPool pool = (KyleDBConnectionPool) 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())
		{
			KyleDBConnectionPool pool = (KyleDBConnectionPool) 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("."));
				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;
				}
				KyleDBConnectionPool pool =
				new KyleDBConnectionPool(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 is = getClass().getResourceAsStream("/db.properties");
		Properties dbProps = new Properties();
		try
		{
			dbProps.load(is);
		}
		catch (Exception e)
		{
			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");
		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);
	}

	
	/**----------------------------------------------------------**/
	/**
	* 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 KyleDBConnectionPool
	{
		private int checkedOut;
		private Vector freeConnections = new Vector();
		private int maxConn;
		private String name;
		private String password;
		private String URL;
		private String user;

		/**
		* 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 KyleDBConnectionPool(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();
		}

		/**
		* 从连接池获得一个可用连接.如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;
			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++;
			}
			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;
			}
			System.out.println(">>>Create newConnection ");
			return con;
		}
	}
}