• “获得数据库连接”操作，将在以后的增删改查所有功能中都存在，可以封装工具类JDBCUtils。提供获取连接对象的方法，从而达到代码的重复利用。

• 该工具类提供方法：public static Connection getConnection()。代码如下：

jdbc.properties文件

jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/day0204_db
jdbc.username=root
jdbc.password=root

通过Properties 读取配置文件内容

@Test
public void demo06() throws Exception {
// 需求6: 读取配置文件内容
// 1 创建对象
Properties props = new Properties();
// 2 加载文件
InputStream in = JDBCTest.class.getClassLoader().getResourceAsStream(“jdbc.properties”);
props.load(in);
// 3 读取内容 且 打印
String url = props.getProperty(“jdbc.url”);
String username = props.getProperty(“jdbc.username”);

System.out.println(url);
System.out.println(username);

}

JDBC工具类

package cn.hanjiaxiaozhi.utils;import cn.hanjiaxiaozhi.JDBCTest;import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;public class JDBCUtils {private static String driverClassName;private static String url;private static String username;private static String password;static {try {// 1 创建对象Properties props = new Properties();// 2 加载文件InputStream in = JDBCTest.class.getClassLoader().getResourceAsStream("jdbc.properties");props.load(in);// 3 读取内容 且 打印driverClassName = props.getProperty("jdbc.driverClassName");url = props.getProperty("jdbc.url");username = props.getProperty("jdbc.username");password = props.getProperty("jdbc.password");// 1 注册驱动Class.forName(driverClassName);} catch (Exception e) {e.printStackTrace();}}// 1 获取连接public static Connection getConnection() throws SQLException {// 2 获取连接Connection conn = DriverManager.getConnection(url, username, password);return conn;}// 2 释放资源public static void release(Connection conn, Statement stmt, ResultSet rs) {try {if(rs!=null) {rs.close();}} catch (SQLException e) {e.printStackTrace();}release(conn, stmt);}public static void release(Connection conn, Statement stmt) {try {if(stmt!=null) {stmt.close();}} catch (SQLException e) {e.printStackTrace();}try {if(conn!=null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}
}

使用JDBC工具类 完成查询

@Testpublic void demo01() {Connection conn = null;PreparedStatement stmt = null;ResultSet rs = null;try {// 2 获取连接conn = JDBCUtils.getConnection();// 3 获取执行sql对象String sql = "select * from tb_user";stmt = conn.prepareStatement(sql);// 4 执行sql 获取结果rs = stmt.executeQuery();// 5 处理结果while (rs.next()) {int uid = rs.getInt("uid");String uname = rs.getString("username");String upwd = rs.getString("password");String nickname = rs.getString("nickname");System.out.println(uid +"============="+ uname +"============="+ upwd +"============="+ nickname);}} catch (SQLException e) {e.printStackTrace();} finally {// 6 释放资源JDBCUtils.release(conn, stmt, rs);}}