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package model.database; import java.io.*; import java.sql.*; import java.util.*; import java.util.Date; public class DBConnectionManager { static private DBConnectionManager instance; // 唯一实例 static private int clients; private Vector<Driver> drivers = new Vector<Driver>(); private PrintWriter log; private Hashtable<String, DBConnectionPool> pools = new Hashtable<String, DBConnectionPool>(); /** * 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; } /** * 建构函数私有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); 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<DBConnectionPool> allPools = pools.elements(); while (allPools.hasMoreElements()) { DBConnectionPool pool = (DBConnectionPool) allPools.nextElement(); pool.release(); } Enumeration<Driver> 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; } 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 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 DBConnectionPool { private int checkedOut; private Vector<Connection> freeConnections = new Vector<Connection>(); 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 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(); } /** * 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 (