package caiwu;

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

public class DBConnectionManager {
 static private DBConnectionManager instance; // 唯一實例
 static private int clients;

 private Vector drivers = new Vector();
 private PrintWriter log;
 private Hashtable pools = new Hashtable();

 /**
  * 返回唯一實例.如果是第一次調用此方法,則創建實例
  *
  * @return DBConnectionManager 唯一實例
  */
 static synchronized public DBConnectionManager getInstance() {
   if (instance == null) {
     instance = new DBConnectionManager();
   }
   clients++;
   return instance;
 }

 /**
  * 建構函數私有以防止其它對象創建本類實例
  */
 private DBConnectionManager() {
   init();
 }

 /**
  * 將連接對象返回給由名字指定的連接池
  *
  * @param name 在屬性文件中定義的連接池名字
  * @param con 連接對象
  */
 public void freeConnection(String name, Connection con) {
   DBConnectionPool pool = (DBConnectionPool) pools.get(name);
   if (pool != null) {
     pool.freeConnection(con);
   }
 }

 /**
  * 獲得一個可用的(空閑的)連接.如果沒有可用連接,且已有連接數小于最大連接數
  * 限制,則創建并返回新連接
  *
  * @param name 在屬性文件中定義的連接池名字
  * @return Connection 可用連接或null
  */
 public Connection getConnection(String name) {
   DBConnectionPool pool = (DBConnectionPool) pools.get(name);
   if (pool != null) {
     return pool.getConnection();
   }
   return null;
 }

 /**
  * 獲得一個可用連接.若沒有可用連接,且已有連接數小于最大連接數限制,
  * 則創建并返回新連接.否則,在指定的時間內等待其它線程釋放連接.
  *
  * @param name 連接池名字
  * @param time 以毫秒計的等待時間
  * @return Connection 可用連接或null
  */
 public Connection getConnection(String name, long time) {
   DBConnectionPool pool = (DBConnectionPool) pools.get(name);
   if (pool != null) {
     return pool.getConnection(time);
   }
   return null;
 }

 /**
  * 關閉所有連接,撤銷驅動程序的注冊
  */
 public synchronized void release() {
   // 等待直到最后一個客戶程序調用
   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("撤銷JDBC驅動程序 " + driver.getClass().getName()+"的注冊");
     }
     catch (SQLException e) {
       log(e, "無法撤銷下列JDBC驅動程序的注冊: " + driver.getClass().getName());
     }
   }
 }

 /**
  * 根據指定屬性創建連接池實例.
  *
  * @param props 連接池屬性
  */
 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("沒有為連接池" + 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("錯誤的最大連接數限制: " + maxconn + " .連接池: " + poolName);
     max = 0;
   }
   DBConnectionPool pool = new DBConnectionPool(poolName, url, user, password, max);
   pools.put(poolName, pool);
   log("成功創建連接池" + poolName);
  }
 }
 }

 /**
  * 讀取屬性完成初始化
  */
  private void init() {
  InputStream is = getClass().getResourceAsStream("/config/caiwu.properties");
  Properties dbProps = new Properties();
  try {
    dbProps.load(is);
  }
  catch (Exception e) {
    System.err.println("不能讀取屬性文件. " +
   "請確保db.properties在CLASSPATH指定的路徑中");
    return;
  }
  String logFile = dbProps.getProperty("logfile", "newslog.txt");
  try {
    log = new PrintWriter(new FileWriter(logFile, true), true);
  }
  catch (IOException e) {
    System.err.println("無法打開日志文件: " + logFile);
    log = new PrintWriter(System.err);
  }
  loadDrivers(dbProps);
  createPools(dbProps);
 }

 /**
  * 裝載和注冊所有JDBC驅動程序
  *
  * @param props 屬性
  */
 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("成功注冊JDBC驅動程序" + driverClassName);
   }
   catch (Exception e) {
     log("無法注冊JDBC驅動程序: " +
     driverClassName + ", 錯誤: " + e);
   }
 }
 }

 /**
  * 將文本信息寫入日志文件
  */
 private void log(String msg) {
//   log.println(new Date() + ": " + msg);
 }

 /**
  * 將文本信息與異常寫入日志文件
  */
 private void log(Throwable e, String msg) {
  // log.println(new Date() + ": " + msg);
  // e.printStackTrace(log);
 }

 /**
  * 此內部類定義了一個連接池.它能夠根據要求創建新連接,直到預定的最
  * 大連接數為止.在返回連接給客戶程序之前,它能夠驗證連接的有效性.
  */
 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;

 /**
  * 創建新的連接池
  *
  * @param name 連接池名字
  * @param URL 數據庫的JDBC URL
  * @param user 數據庫帳號,或 null
  * @param password 密碼,或 null
  * @param maxConn 此連接池允許建立的最大連接數
  */
 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;
   }

  /**
   * 將不再使用的連接返回給連接池
   *
   * @param con 客戶程序釋放的連接
   */
 public synchronized void freeConnection(Connection con) {
   // 將指定連接加入到向量末尾
   freeConnections.addElement(con);
   checkedOut--;
   notifyAll();
 }

 /**
  * 從連接池獲得一個可用連接.如沒有空閑的連接且當前連接數小于最大連接
  * 數限制,則創建新連接.如原來登記為可用的連接不再有效,則從向量刪除之,
  * 然后遞歸調用自己以嘗試新的可用連接.
  */
 public synchronized Connection getConnection() {
   Connection con = null;
   if (freeConnections.size() > 0) {
     // 獲取向量中第一個可用連接
     con = (Connection) freeConnections.firstElement();
     freeConnections.removeElementAt(0);
     try {
       if (con.isClosed()) {
         log("從連接池" + name+"刪除一個無效連接");
         // 遞歸調用自己,嘗試再次獲取可用連接
         con = getConnection();
       }
     }
     catch (SQLException e) {
       log("從連接池" + name+"刪除一個無效連接");
       // 遞歸調用自己,嘗試再次獲取可用連接
       con = getConnection();
     }
    }
    else if (maxConn == 0 || checkedOut < maxConn) {
con = newConnection();
}
if (con != null) {
checkedOut++;
}
return con;
}

/**
* 從連接池獲取可用連接.可以指定客戶程序能夠等待的最長時間
* 參見前一個getConnection()方法.
*
* @param timeout 以毫秒計的等待時間限制
*/
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()返回的原因是超時
        return null;
      }
    }
    return con;
  }

 /**
  * 關閉所有連接
  */
 public synchronized void release() {
   Enumeration allConnections = freeConnections.elements();
   while (allConnections.hasMoreElements()) {
     Connection con = (Connection) allConnections.nextElement();
     try {
       con.close();
       log("關閉連接池" + name+"中的一個連接");
     }
     catch (SQLException e) {
       log(e, "無法關閉連接池" + name+"中的連接");
     }
   }
   freeConnections.removeAllElements();
 }

 /**
  * 創建新的連接
  */
 private Connection newConnection() {
 Connection con = null;
 try {
 if (user == null) {
 con = DriverManager.getConnection(URL);
 }
 else {
 con = DriverManager.getConnection(URL, user, password);
 }
 log("連接池" + name+"創建一個新的連接");
 }
 catch (SQLException e) {
 log(e, "無法創建下列URL的連接: " + URL);
 return null;
 }
 return con;
 }


 }
 }