drivername=com.mysql.jdbc.Driver

url=jdbc:mysql://localhost:3306/mydb

user=root

password=root

package com.gordon.jdbcutil;

import java.io.InputStream;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.util.Properties;

public class JDBCUtil {

	public static String DRIVERNAME = null;

	public static String URL = null;

	public static String USER = null;

	public static String PASSWORD = null;

	public static Connection conn = null;

	static {

		try {

			Properties props = new Properties();

			//Reader in = new FileReader("db.properties");

			InputStream in = JDBCUtil.class.getClassLoader().getResourceAsStream("db.properties");

			props.load(in);

			DRIVERNAME = props.getProperty("drivername");

			URL = props.getProperty("url");

			USER = props.getProperty("user");

			PASSWORD = props.getProperty("password");

		} catch (Exception e) {

			throw new RuntimeException(e);

		}

	}

	public static Connection getConnection() throws Exception {

		if (conn != null) {

			return conn;

		}

		Class.forName(DRIVERNAME);

		conn = DriverManager.getConnection(URL, USER, PASSWORD);

		return conn;

	}

	public static void closeResource(Connection conn, PreparedStatement st) throws SQLException {

		st.close();

		conn.close();

	}

	public static void closeResource(Connection conn, ResultSet rs, PreparedStatement st) throws SQLException {

		st.close();

		rs.close();

		conn.close();

	}

}

package com.gordon.jdbc;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import com.gordon.jdbcutil.JDBCUtil;

public class jdbc01 {

	public static void main(String[] args) {

		selectFunction();

	}

	public static void selectFunction() {

		try {

			//1.获取连接

			Connection conn = JDBCUtil.getConnection();

			// 3.sql语句

			String sql = "SELECT * FROM user";

			// 3.获取SQL执行者

			PreparedStatement st = conn.prepareStatement(sql);

			// 4.设置参数

			// 5.执行sql语句

			ResultSet rs = st.executeQuery();

			// 6.处理数据

			while (rs.next()) {

				System.out.println(rs.getString("id") + ":" + rs.getString("name"));

			}

			// 7.释放资源

			JDBCUtil.closeResource(conn, rs, st);

		} catch (SQLException ex) {

			System.out.println(ex.getMessage());

		} catch (Exception e) {

			System.out.println(e.getMessage());

		}

	}

}