判断用户名是否存在

dao接口：

//检测用户名是否重复
public User checkUserName(String userName);

dao实现类：

//检测用户名是否重复
	@Override
	public User checkUserName(String userName) {
		Connection conn = DBUtil.getConnection();
		PreparedStatement ps = null;
		ResultSet rs = null;
		User user=null;
		String sql="SELECT USER_NAME FROM T_USER WHERE USER_NAME = ? ";
		try {
			ps=conn.prepareStatement(sql);
			ps.setString(1, userName);
			rs=ps.executeQuery();
			while(rs.next()) {
				user=new User();
				user.setUserName(rs.getString("USER_NAME"));				
			}
		} catch (SQLException e) {
			
			e.printStackTrace();
		}finally {
			DBUtil.closeConn(conn, ps, rs);
		}
		
		return user;
	}

建一个类来测试：

package com.cyzy.dao;

import com.cyzy.bean.User;

public class UserDaoTest {
	public static void main(String[] args) {
		UserDao userDao=new UserDaoImpl();
		User user=new User(0, "zhangxiaoxiao", null, null, 0, null, 0);
		User users=userDao.checkUserName(user.getUserName());
		if(users !=null) {
			System.out.println("用户存在!!!");
		}else {
			System.out.println("用户不存在!!!");
		}
	}
}

检测到zhangxiaoxiao用户名已存在

检测到zhangsan用户名不存在

 

 

来源：CSDN

作者：走到天涯海角

链接：https://blog.csdn.net/weixin_42995083/article/details/104591739