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连接池管理类DBConnectionManager

原创 Linux操作系统 作者:faq_dog 时间:2011-06-14 11:27:18 0 删除 编辑

package co.utl;
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("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
         * @throws FileNotFoundException
         */
        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");
                                String minconn = props.getProperty(poolName + ".minConns", "0");
                                String strloginterval = props.getProperty(poolName + ".logInterval", "0");
                                int max;
                                int min;
                                long logInterval = Long.parseLong(strloginterval);
                                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;
        }
        try {
         min = Integer.valueOf(minconn).intValue();
        } catch (NumberFormatException e) {
         log("错误的最小连接数限制: " + minconn + " .连接池: " + poolName);
         min = 0;
        }
                                DBConnectionPool pool = new DBConnectionPool(poolName, url, user, password, max, min,logInterval);
                                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("/db.properties");
                Properties dbProps = new Properties();
                try {
                        dbProps.load(is);
                } 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");
                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);
        }

        /**
         * 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 final int SLEEP_INTERVAL = 10000;
          
                private int checkedOut; //被占用的链接数

                private Vector freeConnections = new Vector();

                private int maxConn;
               
                private int minConn;

                private String name;

                private String password;

                private String URL;

                private String user;
               
                private long logTimer;
               
          private long logInterval;
          
          private Thread poolMonitor;

                /**
                 * 创建新的连接池连;接池始终保持一定数量的连接.当申请连接时如果连接池中连接数小于定值
                 *  则申请新的连接 连接池设置监控线程每个一段时间就扫描池中的连接如果不可用则删除之并记录连接池的状态
                 *
                 * @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
                 * @param minConn 最小链接数
                 */
                public DBConnectionPool(String name, String URL, String user, String password, int maxConn,
                  int minConn, long logInterval) {
                        this.name = name;
                        this.URL = URL;
                        this.user = user;
                        this.password = password;
                        this.maxConn = maxConn;
                        this.minConn = minConn;
               this.logInterval = logInterval;
               
               for (int i = 0; i < minConn; i++) {
                Connection initConn = newConnection();
                freeConnections.addElement(initConn);
               }
               logTimer = System.currentTimeMillis();
               poolMonitor = new Thread(new Runnable() {
                public void run() {
                 monitor();
                }
               });
               poolMonitor.start();
                }
                /**
                 * 监听程序 判断线程空闲的时间是否足够长,如果太长,则断开该链接
                 *
                 */
          private void monitor() {
           while (true) {
            // /每隔logInterval对连接池清理一次,删除无效连接,后者在很长一段时间没有使用的连接
            if ((System.currentTimeMillis() - logTimer) > logInterval) {
             Enumeration checkconn = freeConnections.elements();
             while (checkconn.hasMoreElements()) {
              Connection con = (Connection) checkconn.nextElement();
              try {
               if (con == null || con.isClosed()) {
                freeConnections.removeElement(con);
                log("关闭连接池" + name + "中的一个连接");
                log("从连接池" + name + "目前可使用连接数" + freeConnections.size()); 
               }else  if (freeConnections.size() > minConn) {
                con.close();
                freeConnections.removeElement(con);
                log("关闭连接池" + name + "中的一个连接");
                log("从连接池" + name + "目前可使用连接数" + freeConnections.size());  
               }
              } catch (SQLException e) {
               System.out.println("momitor 出错!");
              }
             }
             while (freeConnections.size() < minConn) {
              Connection con = newConnection();
              freeConnections.addElement(con);
        log("从连接池" + name + "目前可使用连接数" + freeConnections.size());
             }
             logTimer = System.currentTimeMillis();
            }
            try {
             Thread.sleep(SLEEP_INTERVAL);
            } catch (InterruptedException e) {
             System.out.println("监控线程被打断!!");
            }
           }
          }

                /**
                 * 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--;
                        log("从连接池" + name + "被占用的链接数" + checkedOut);
                        log("从连接池" + name + "目前可使用连接数" + freeConnections.size());
                        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");
                                                log("从连接池" + name + "目前可使用连接数" + freeConnections.size());
                                                // 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++;
                                log("从连接池" + name + "被占用的链接数" + 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("无法创建下列URL的连接: " + URL + "\n\t" + e.getNextException());
                                return null;
                        }
                        return con;
                }
        }

}


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