单例实现连接池

Java code

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package fx.sql;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * 
 * 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.
 * 
 * @author FX
 * 
 */
public class DBConnectionPool {
    /**
     * 传说中的连接池
     */
    private List<Connection> freeConnections =
 new ArrayList<Connection>();
    private Connection con = null;
    private int connect = 0; // 使用的连接数

    private int maxConn; // 最大连接
    @SuppressWarnings("unused")
    private String name; // 连接池名字
    private String driver; // 驱动
    private String url; // 数据库连接地址
    private String user; // 用户名
    private String password;// 密码

    /**
     * 有惨构造创建连接池
     * 
     * @param driver
     * @param name
     * @param URL
     * @param user
     * @param password
     * @param maxConn
     */
    public DBConnectionPool(String name, String driver, String URL,
            String user, String password, int maxConn) {
        this.name = name;
        this.driver = driver;
        this.url = URL;
        this.user = user;
        this.password = password;
        this.maxConn = maxConn;
        poolInfo();
    }

    /**
     * 显示准备创建连接池的信息
     */
    private void poolInfo() {
        Connection conn = this.newConnection();
        freeConnections.add(conn);
        for (int i = 0; i < this.maxConn - 1; i++) {
            Connection freeConn = conn;
            freeConnections.add(freeConn);
        }
    }

    /**
     * 用完，释放连接
     * 
     * @param con
     *            释放一个连接
     */
    public synchronized void freeConnection(Connection con) {
        this.freeConnections.add(con);
        this.connect--;
    }

    /**
     * 从连接池中获取一个可用连接
     * 
     * 当无法从池中获取可用连接时,新创建一个连接
     * 
     * @return 返回连接对象
     */
    public synchronized Connection getConnection() {
        if (this.freeConnections.size() > 0) {
            con = this.freeConnections.get(0);
            /**
             * 当在池中取出一个连接后,删除此连接
             */
            this.freeConnections.remove(0);
            /**
             * 当取出的连接为null时,递归调用自己,直到获得一个可用连接为止
             */
            if (con == null)
                con = getConnection();
        } else {
            con = newConnection();
        }
        if (this.maxConn == 0 || this.maxConn < this.connect) {
            /**
             * 等待 超过最大连接时
             */
            con = null;
        }
        if (con != null) {
            this.connect++;
        }
        return con;
    }

    /**
     * 释放全部连接
     * 
     */
    public synchronized void release() {
        Iterator<Connection> allConns = this.freeConnections.iterator();
        while (allConns.hasNext()) {
            Connection conn = (Connection) allConns.next();
            try {
                if (null != conn) {
                    conn.close();
                }
                conn = null;
            } catch (SQLException e) {
                e.printStackTrace();
            }

        }
        this.freeConnections.clear();

    }

    /**
     * 创建一个数据库连接对象
     * 
     * @return 返回数据库连接
     */
    private Connection newConnection() {
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e2) {

            e2.printStackTrace();
        }
        try {
            con = DriverManager.getConnection(url, user, password);
        } catch (SQLException e1) {
            e1.printStackTrace();
            System.exit(0);
        }
        return con;
    }
}

Java code

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package fx.sql;

import java.sql.Connection;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.Hashtable;

import fx.toolkit.Evn;

/**
 * 连接池的管理类,负责读取配置连接池的文件,并创建连接池
 * 
 * 从池中获取,释放连接
 * 
 * @author FX
 * 
 */
public class DBConnectionManager {
    /**
     * 唯一数据库连接池管理实例类
     * 
     * 使用单例模式创建
     */
    private static DBConnectionManager instance;
    /**
     * 连接池的集合,
     */
    private Hashtable<String, DBConnectionPool> pools = 
new Hashtable<String, DBConnectionPool>();

    /**
     * 得到唯一实例管理类
     * 
     * @return 一个连接池的管理类
     */
    public static synchronized DBConnectionManager getInstance() {
        if (instance == null) {
            instance = new DBConnectionManager();
        }
        return instance;

    }

    /**
     * 只允许内部实例化管理类
     */
    private DBConnectionManager() {
        this.init();
    }

    /**
     * 加载驱动程序
     */
    private void init() {
        Evn evn = new Evn("/db.properties");
        String name = evn.getProperty("name");
        String driver = evn.getProperty("driver");
        String url = evn.getProperty("url");
        String user = evn.getProperty("user");
        String password = evn.getProperty("password");
        int maxConn = Integer.parseInt(evn.getProperty("maxConn"));
        DBConnectionPool pool = new DBConnectionPool(name, driver, url, user,
                password, maxConn);
        pools.put(name, pool);
    }

    /**
     * 根据连接池的名字得到一个连接
     * 
     * @param name
     *            连接池的名称
     * @return 池中的一个可用连接
     */
    public Connection getConnection(String name) {
        DBConnectionPool pool = null;
        Connection con = null;
        pool = pools.get(name);
        try {
            con = pool.getConnection();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return con;
    }

    /**
     * 释放一个连接
     * 
     * @param name
     *            连接池的名称
     * @param con
     *            将要是释放的连接对象
     */
    public synchronized void freeConnection(String name, Connection con) {
        DBConnectionPool pool = pools.get(name);// 根据连接池名称得到连接池
        if (pool != null)
            pool.freeConnection(con);// 释放连接
    }

    /**
     * 释放所有连接
     */
    public synchronized void release() {
        Enumeration<DBConnectionPool> allpools = pools.elements();
        while (allpools.hasMoreElements()) {
            DBConnectionPool pool = allpools.nextElement();
            if (pool != null)
                pool.release();
        }
        pools.clear();
    }

    public static void main(String[] args) throws SQLException {
        DBConnectionManager manager = new DBConnectionManager();
        Connection conn = manager.getConnection("fxConnPool");
        conn.close();
    }
}