import java.sql.*;import java.io.*;import java.util.*;public class DBConnectionManager { private static int clients = 0; private static DBConnectionManager instance; private Vector drivers = new Vector(); private PrintWriter log; private Hashtable pools = new Hashtable(); public DBConnectionManager() { init(); } private void log(String msg) { log.println(new java.util.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 java.util.Date() + ": " + msg); e.printStackTrace(log); } public static synchronized DBConnectionManager getInstance() { if (instance == null) { instance = new DBConnectionManager(); } clients++; return instance; } private void init() { InputStream is = getClass().getResourceAsStream("/db.properties"); Properties dbProps = new Properties(); try { dbProps.load(is); } catch (Exception e) { System.err.println("Can not read the properties file. " + "Make sure db.properties is in the CLASSPATH"); return; } loadDrivers(dbProps); createPools(dbProps); } public void freeConnection(String name, Connection con) { DBConnectionPool pool = (DBConnectionPool) pools.get(name); if (pool != null) { pool.freeConnection(con); } } public Connection getConnection(String name) { DBConnectionPool pool = (DBConnectionPool) pools.get(name); if (pool != null) { return pool.getConnection(); } return null; } public Connection getConnection(String name, long time) { DBConnectionPool pool = (DBConnectionPool) pools.get(name); if (pool != null) { return pool.getConnection(time); } return null; } 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()); } } }/*drivers=sun.jdbc.odbc.JdbcOdbcDriver jdbc.idbDriverlogfile=D://user//src//java//DBConnectionManager//log.txtidb.url=jdbc:idb:c://local//javawebserver1.1//db//db.prpidb.maxconn=2access.url=jdbc:odbc:demoaccess.user=demoaccess.password=demopw*/ 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.log("Registered JDBC driver " + driverClassName); } catch (Exception e) { // Log.log("Can not register JDBC driver: " + driverClassName + ", Exception: " + e.toString())); } } } 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.log("No URL specified for " + poolName); 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.log("Invalid maxconn value " + maxconn + " for " + poolName); max = 0; } DBConnectionPool pool = new DBConnectionPool(poolName, url, user, password, max); pools.put(poolName, pool); // Log.log("Initialized pool " + poolName); } } } class DBConnectionPool { 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 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 java.util.Date().getTime(); Connection con; while ((con = getConnection()) == null) { try { wait(timeout); } catch (InterruptedException e) {} if ((new java.util.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; } }}
