import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.SQLException;
import java.util.Properties;
import java.util.Vector;

public class ConnectionPool {

	private Vector<Connection> pool;

	private String url;

	private String username;

	private String password;

	private String driverClassName;

	/**
	 * 连接池的大小，也就是连接池中有多少个数据库连接。
	 */
	private int poolSize = 1;

	private static ConnectionPool instance = null;

	/**
	 * 私有的构造方法，禁止外部创建本类的对象，要想获得本类的对象，通过<code>getIstance</code>方法。
	 * 使用了设计模式中的单子模式。
	 */
	private ConnectionPool() {
		init();
	}

	/**
	 * 连接池初始化方法，读取属性文件的内容 建立连接池中的初始连接
	 */
	private void init() {
		pool = new Vector<Connection>(poolSize);
		readConfig();
		addConnection();
	}

	/**
	 * 返回连接到连接池中
	 */
	public synchronized void release(Connection conn) {
		pool.add(conn);

	}

	/**
	 * 关闭连接池中的所有数据库连接
	 */
	public synchronized void closePool() {
		for (int i = 0; i < pool.size(); i++) {
			try {
				((Connection) pool.get(i)).close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
			pool.remove(i);
		}
	}

	/**
	 * 返回当前连接池的一个对象
	 */
	public static ConnectionPool getInstance() {
		if (instance == null) {
			instance = new ConnectionPool();
		}
		return instance;
	}

	/**
	 * 返回连接池中的一个数据库连接
	 */
	public synchronized Connection getConnection() { 
		if (pool.size() > 0) {
			Connection conn = pool.get(0);
			pool.remove(conn);
			return conn;
		} else {
			return null;
		}
	}

	/**
	 * 在连接池中创建初始设置的的数据库连接
	 */
	private void addConnection() {
		Connection conn = null;
		for (int i = 0; i < poolSize; i++) {

			try {
				Class.forName(driverClassName);
				conn = java.sql.DriverManager.getConnection(url, username, password);
				pool.add(conn);

			} catch (ClassNotFoundException e) {
				e.printStackTrace();
			} catch (SQLException e) {
				e.printStackTrace();
			}

		}
	}

	/**
	 * 读取设置连接池的属性文件
	 */
	private void readConfig() {
		try {
			String path = System.getProperty("user.dir") + "\\dbpool.properties";
			FileInputStream is = new FileInputStream(path);
			Properties props = new Properties();
			props.load(is);
			this.driverClassName = props.getProperty("driverClassName");
			this.username = props.getProperty("username");
			this.password = props.getProperty("password");
			this.url = props.getProperty("url");
			this.poolSize = Integer.parseInt(props.getProperty("poolSize"));
		} catch (Exception e) {
			e.printStackTrace();
			System.err.println("读取属性文件出错. ");
		}
	}
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class ConnectionPoolTest {
	public static void main(String[] args) throws Exception {
		String sql = "select id,name,phone from guestbook";
		long start = System.currentTimeMillis();
		ConnectionPool pool = null;

		for (int i = 0; i < 100; i++) {
			pool = ConnectionPool.getInstance();
			Connection conn = pool.getConnection();
			Statement stmt = conn.createStatement();
			ResultSet rs = stmt.executeQuery(sql);
			while (rs.next()) {
			}
			rs.close();
			stmt.close();
			pool.release(conn);
		}
		pool.closePool();
		System.out.println("经过100次的循环调用，使用连接池花费的时间:"
				+ (System.currentTimeMillis() - start) + "ms\n");

		String hostName = "192.168.213.144";
		String driverClass = "oracle.jdbc.driver.OracleDriver";
		String url = "jdbc:oracle:thin:@" + hostName + ":1521:orcl";
		String user = "scott";
		String password = "tiger";
		start = System.currentTimeMillis();

		for (int i = 0; i < 100; i++) {
			Class.forName(driverClass);
			Connection conn = DriverManager.getConnection(url, user, password);
			Statement stmt = conn.createStatement();
			ResultSet rs = stmt.executeQuery(sql);
			while (rs.next()) {
			}
			rs.close();
			stmt.close();
			conn.close();
		}
		S