jdbc连接池

/** 
 * 数据库连接池管理类 
 */ 
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 {  
      
    public static void main(String[] args) {  
        DBConnectionManager connectionManager = DBConnectionManager.getInstance();  
          
        Connection conn =  connectionManager.getConnection("idb");  
            try {  
                Thread.sleep(10);  
            } catch (InterruptedException e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
            }  
        Connection conn1 =  connectionManager.getConnection("idb");  
        Connection conn2 =  connectionManager.getConnection("idb");  
        Connection conn3 =  connectionManager.getConnection("idb");  
        Connection conn4 =  connectionManager.getConnection("idb");  
        Connection conn5 =  connectionManager.getConnection("idb");  
        connectionManager.freeConnection("idb", conn);  
        connectionManager.freeConnection("idb", conn1);  
        connectionManager.freeConnection("idb", conn2);  
        connectionManager.freeConnection("idb", conn3);  
        connectionManager.freeConnection("idb", conn4);  
        connectionManager.freeConnection("idb", conn5);  
        Connection conn6 = connectionManager.getConnection("idb");  
        Connection conn7 = connectionManager.getConnection("idb");  
        System.out.println(" conn6 == "+conn6 +" conn7 == "+conn7);  
          
    }  
 
      
    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;  
    }  
 
    /** 
     * 建构私有函数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);  
        //System.out.println(" pool == "+pool);  
        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("."));  
                //System.out.println(" poolName ||"+poolName+"|");  
                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 fileinputstream = null;  
        try {  
            fileinputstream = new FileInputStream("./src/db.properties");  
        } catch (FileNotFoundException e1) {  
            e1.printStackTrace();  
        }  
        //BufferedReader bufferedreader = new BufferedReader(new InputStreamReader(fileinputstream));  
 
        //InputStream is = getClass().getResourceAsStream("D:/workspace/UmessageSms/src/db.properties");  
        Properties dbProps = new Properties();  
        try {  
            dbProps.load(fileinputstream);  
        } catch (Exception e) {  
            e.printStackTrace();  
            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");  
          
        //System.out.println(dbProps.getProperty("logfile"));  
        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);  
    }  
 
    /** ************************************************************* */ 
    /** ********************内部类DBConnectionPool******************** */ 
    /** ************************************************************* */ 
    /** 
     * 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; // 当前连接数  
 
        private Vector freeConnections = new Vector(); // 保存所有可用连接  
 
        private int maxConn; // 此连接池允许建立的最大连接数  
 
        private String name; // 连接池名字  
 
        private String password; // 密码或null  
 
        private String URL; // 数据库的JDBC URL  
 
        private String user; // 数据库账号或null  
 
        /** 
         * 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(); // 删除等待队列中的所有线程  
        }  
 
        /** 
         * 从连接池获得一个可用连接.如果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;  
            //System.out.println(" freeConnections.size() "+freeConnections.size());  
            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++;  
            }  
            System.out.println("con == "+con);  
            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;  
        }  
    }  
}