dbconnectionmanager.java

图书管理系统,B/S,C/S都有,附有源代码

package database;

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

/**
 * <p>Title: library</p>
 * <p>Description: library</p>
 * <p>Copyright: Copyright (c) 2007</p>
 * <p>Company: </p>
 * @author nino
 * @version 0.1
 */

public class DBConnectionManager {

  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 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("."));
      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 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 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;
  }
  }

}