J2SE——数据库连接池的创建

/**
 * A)当用户调用pool = ConnectionPool.getInstance(username,password)方法时<br>
 * 执行构造方法--> 调用init()方法(1.读取配置文件中的driverClassName,url并设置, <br>
 *                            2.创建Vector容器<br>
 *                            3.addConn():通过driverClassName,url,username,password 向容器中添加Connection对象)<br>
 * B)conn = pool.getConn();//得到Connection对象.
 * C)conn用完后不是调用close()方法而是调用 release()方法,将连接放回池中
 * D)退出程序时调用 closeAllConnection()方法关闭所有连接
 */
public class ConnectionPool {
	private String driverClassName;

	private String url;

	private String username;

	private String password;

	private Vector<Connection> pool;

	private int poolSize = 1;

	private static ConnectionPool instance;

	private ConnectionPool(String username, String password) {
		this.username = username;
		this.password = password;
		init();
	}

	public static ConnectionPool getInstance(String username, String password) {
		if (instance == null) {
			instance = new ConnectionPool(username, password);
		}
		return instance;
	}

	/**
	 * 如果容器中有Connection 返回一个并从容器中移除<br>
	 * 否则返回NULL
	 */
	public synchronized Connection getConn() {
		if (pool.size() > 0) {
			Connection conn = pool.get(0);
			pool.remove(0);
			return conn;
		}
		return null;
	}

	public synchronized void release(Connection conn) {
		pool.add(conn);
	}

	public synchronized void closeAllConnection() {
		for (int i = 0; i < pool.size(); i++) {
			try {
				pool.get(i).close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
			pool.remove(i);
		}
	}

	private void init() {
		readConfig();// 读取配置文件中的url
		pool = new Vector<Connection>(poolSize);
		addConn();
	}

	private void readConfig() {
		FileInputStream input = null;
		try {
			input = new FileInputStream(System.getProperty("user.dir")
					+ "/data/db.properties");
		} catch (FileNotFoundException e1) {
			e1.printStackTrace();
		}

		Properties pro = new Properties();
		try {
			pro.load(input);
			driverClassName = (String) pro.get("driverClassName");
			url = (String) pro.get("url");
			poolSize = Integer.parseInt((String) pro.get("poolSize"));
		} catch (IOException e) {
			e.printStackTrace();
			// 如果读取属性出错

		} finally {
			if (input != null) {
				try {
					input.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}

	}


	private void addConn() {
		Connection conn = null;
		try {
			for (int i = 0; i < poolSize; i++) {
				Class.forName(driverClassName);
				conn = DriverManager.getConnection(url, username, password);
				pool.add(conn);
			}
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
			// driverClassName 错误时
		} catch (SQLException e) {
			e.printStackTrace();
			// url, username, password错误时
		}
	}

}