dbconnectionmanager.java

小虫新闻管理系统 V1.0(jsp+javabean+mysql)

package news.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 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("/news.txt");
  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", "newslog.txt");
  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("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;
   private String databaseUrl;

 /**
  * 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; 
 } 
 

 }
 }