package zhaobiao.db;import java.io.*;import java.sql.*;import java.util.*;import java.util.Date;/**連接池 * 管理類DBConnectionManager支持對一個或多個由屬性文件定義的數據庫連接 * 池的訪問.客戶程序可以調用getInstance()方法訪問本類的唯一實例. */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("db.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", "DBConnectionManager.log");    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("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;    /**     * 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;    }  }}