dbconnectionmanager.java

JAVA写的BBS

package com.laoer.bbscs.db;

/**
 * Title:        BBS-CS
 * Description:  BBS-CS(BBS式虚拟社区系统)
 * Copyright:    Copyright (c) 2002
 * Company:      loveroom.com.cn
 * @author laoer
 * @version 3.0
 */

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

/**
* 管理类DBConnectionManager支持对一个或多个由属性文件定义的数据库连接
* 池的访问.客户程序可以调用getInstance()方法访问本类的唯一实例.
*/
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("Deregistered JDBCdriver " + driver.getClass().getName());
        }
        catch (SQLException e) {
            //log(e, "Can not deregistered JDBC driver: " + 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("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("Invalid maxconn value: " + maxconn + " .for: " + poolName);
                max = 0;
            }
            DBConnectionPool pool =
            new DBConnectionPool(poolName, url, user, password, max);
            pools.put(poolName, pool);
            //log("Initialized pool:" + 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("Can not read the properties file; " + "Make sure db.properties is in the Classpath");
        return;
    }
    String logFile = dbProps.getProperty("logfile", "DBConnectionManager.log");
    try {
        log = new PrintWriter(new FileWriter(logFile, true), true);
    }
    catch (IOException e) {
        System.err.println("Can not open the log files: " + 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("Registered JDBC driver:" + driverClassName);
        }
        catch (Exception e) {
            //log("Can not register JDBC driver " + driverClassName + ",Exception:" + 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("Removed bad connection from " + name);
                // 递归调用自己,尝试再次获取可用连接
                con = getConnection();
            }
        }
        catch (SQLException e) {
            //log("Removed bad connection from " + name);
            // 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("Closed connection for pool " + name);
        }
        catch (SQLException e) {
            //log(e, "Can not close connection for pool " + name);
        }
    }
    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("Created a new Connection in pool " + name);
    }
    catch (SQLException e) {
        //log(e, "Can not create a new Connection for " + URL);
        return null;
    }
    return con;
}

}
}