登錄功能的設計

1 使用PreparedStatement語句求(賬號)跟（密碼）的設計

    @Test
    public void tast1() throws Exception {
        Connection conn = JdbcUtil.INSTANCE.getConn();
        String sql = "SELECT * FROM t_user where username = ? and password = ?";
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setString(1, "admin");   //輸入賬號admin
        ps.setString(2, "1");       //輸入密碼1
        ResultSet rs = ps.executeQuery();
        if(rs.next()){
            System.out.println("ok啦....");
        }else{
            System.out.println("nook啦....");
        }
        JdbcUtil.INSTANCE.close(conn, ps, rs);
    }

2 使用Statement語句求（賬號）跟（密碼）的設計

@Test
    public void tast1_1() throws Exception {
        Connection conn = JdbcUtil.INSTANCE.getConn();
        Statement st = conn.createStatement();
        //直接輸入賬號admin 跟 密碼1
        String sql = "SELECT * FROM t_user where username = 'admin' and password = '1'";
        ResultSet rs = st.executeQuery(sql);
        if(rs.next()){
            System.out.println("ok啦....");
        }else{
            System.out.println("nook啦....");
        }
        JdbcUtil.INSTANCE.close(conn, st, rs);
    }

3 使用PreparedStatement中 count(*） 列的設計

@Test
    public void tast2() throws Exception {
        Connection conn = JdbcUtil.INSTANCE.getConn();
        String sql = "SELECT count(*) FROM t_user where username = ? and password = ?";
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setString(1, "admin");
        ps.setString(2, "1");
        ResultSet rs = ps.executeQuery();
        if(rs.next()){
            Long i = rs.getLong(1);
            if(i == 1){
                System.out.println("ok啦....");//此時查找出來的count(*)列的參數爲1密碼正確
            }else{
                System.out.println("nook啦....");//此時查詢出來的count(*)參數爲0，密碼不正確
            }
        }
        JdbcUtil.INSTANCE.close(conn, ps, rs);
    }

4 使用PreparedStatement 告訴（賬號）求（密碼）列的設計

@Test
    public void tast3() throws Exception {
        Connection conn = JdbcUtil.INSTANCE.getConn();
        String sql = "SELECT password FROM t_user where username = ?";
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setString(1, "admin");     //此處輸入賬號
        ResultSet rs = ps.executeQuery();
        if(rs.next()){
            String pwd = rs.getString(1);
            if(pwd.equals("1")){     //此處輸入密碼
                System.out.println("ok啦....");//密碼正確
            }else{
                System.out.println("錯誤啦....");//密碼錯誤
            }
        }else{
            System.out.println("沒有該賬號");
        }
        JdbcUtil.INSTANCE.close(conn, ps, rs);
    }