JDBC工具類的練習（賬號的登錄）

需求：

1. 通過鍵盤錄入用戶名和密碼

2. 判斷用戶是否登錄成功

• select * from user where username = “” and password = “”;
  * 如果這個sql有查詢結果，則成功，反之，則失敗

步驟：

1、創建數據庫表

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、代碼實現

public class JDBCDemo9 {

			    public static void main(String[] args) {
			        //1.鍵盤錄入，接受用戶名和密碼
			        Scanner sc = new Scanner(System.in);
			        System.out.println("請輸入用戶名：");
			        String username = sc.nextLine();
			        System.out.println("請輸入密碼：");
			        String password = sc.nextLine();
			        //2.調用方法
			        boolean flag = new JDBCDemo9().login(username, password);
			        //3.判斷結果，輸出不同語句
			        if(flag){
			            //登錄成功
			            System.out.println("登錄成功！");
			        }else{
			            System.out.println("用戶名或密碼錯誤！");
			        }

}

 /**
			     * 登錄方法
			     */
			    public boolean login(String username ,String password){
			        if(username == null || password == null){
			            return false;
			        }
			        //連接數據庫判斷是否登錄成功
			        Connection conn = null;
			        Statement stmt =  null;
			        ResultSet rs = null;
			        //1.獲取連接
			        try {
			            conn =  JDBCUtils.getConnection();
			            //2.定義sql
			            String sql = "select * from user where username = '"+username+"' and password = '"+password+"' ";
			            //3.獲取執行sql的對象
			            stmt = conn.createStatement();
			            //4.執行查詢
			            rs = stmt.executeQuery(sql);
			            //5.判斷
			           /* if(rs.next()){//如果有下一行，則返回true
			                return true;
			            }else{
			                return false;
			            }*/
			           return rs.next();//如果有下一行，則返回true
			
			        } catch (SQLException e) {
			            e.printStackTrace();
			        }finally {
			            JDBCUtils.close(rs,stmt,conn);
			        }