* 目的:简化书写
* 分析:
1. 注册驱动也抽取
2. 抽取一个方法获取连接对象
* 需求:不想传递参数(麻烦),还得保证工具类的通用性。
* 解决:配置文件
jdbc.properties
url=
user=
password=
3.抽取一个方法释放资源
代码实现:
public class JDBCUtils { private static String url; private static String user; private static String password; private static String driver; /** * 文件的读取,只需要读取一次即可拿到这些值,使用静态代码块 */ static { // 读取资源文件 try { // 1.创建Properties集合类 Properties pro = new Properties(); //2.加载文件 pro.load(new FileReader("src/jdbc.properties")); //3.获取数据 赋值 url = pro.getProperty("url"); user = pro.getProperty("user"); password = pro.getProperty("password"); driver = pro.getProperty("driver"); //4.注册驱动 Class.forName(driver); } catch (IOException | ClassNotFoundException e) { throw new RuntimeException(e); } } /** * 获取连接 * * @return 连接对象 */ public static Connection getConnection() throws SQLException { return DriverManager.getConnection(url,user,password); } /** * 释放资源 * * @param rs * @param stmt * @param conn */ public static void close(ResultSet rs, Statement stmt, Connection conn) { if (rs != null) { try { rs.close(); } catch (SQLException e) { throw new RuntimeException(e); } } if (stmt != null) { try { stmt.close(); } catch (SQLException e) { throw new RuntimeException(e); } } if (conn != null) { try { conn.close(); } catch (SQLException e) { throw new RuntimeException(e); } } } }
* 练习:
* 需求:
1. 通过键盘录入用户名和密码
2. 判断用户是否登录成功
* select * from user where username = "" and password = "";
* 如果这个sql有查询结果,则成功,反之,则失败
* 步骤:
1. 创建数据库表 user
CREATE TABLE USER( id INT PRIMARY KEY AUTO_INCREMENT, username VARCHAR(32), PASSWORD VARCHAR(32) ); INSERT INTO USER VALUES(NULL,'zhangsan','123'); INSERT INTO USER VALUES(NULL,'lisi','234');
2.代码实现:
public static void main(String[] args) { // 1.键盘录入,接受用户名和密码 Scanner sc = new Scanner(System.in); System.out.println("请输入用户名:"); String username = sc.next(); System.out.println("请输入用户密码:"); String password = sc.next(); // 2.调用方法 boolean flag = new jdbcDemo09().login(username, password); //3.判断结果,输出不同语句 if (flag){ //登录成功 System.out.println("登录成功"); }else { System.out.println("用户名或密码错误!"); } } /** * 登录方法 */ public boolean login(String username,String password){ // 判断账号密码是否为空 if (username==null || password==null){ return false; } // 连接数据库判断是否登录成功 Connection conn = null; Statement stmt = null; ResultSet rs = null; try { // 1.获取连接 conn = JDBCUtils.getConnection(); // 2.定义SQL String sql = "select * from user where username='"+username+"' and password = '"+password+"' "; // 3.获取执行SQL的对象 stmt = conn.createStatement(); //4.执行查询 rs = stmt.executeQuery(sql); //5.判断 return rs.next(); } catch (SQLException e) { throw new RuntimeException(e); } }
标签:username,JDBC,String,登录,练习,null,static,new,password From: https://www.cnblogs.com/xuche/p/16802240.html