JavaWeb学习-MVC基础开发系列-6-验证用户名是否存在

素颜马尾好姑娘i 2022-04-25 09:04 779阅读 0赞

继续来做用户注册场景的验证问题，我们还有一个场景没有做，就是注册的时候没有判断用户名是否存在，如果存在就提醒用户换一个用户名再注册。

1.dao接口添加一个根据用户名查找方法

package com.anthony.dao;
    
    import com.anthony.domain.User;
    
    public interface UserDao {
    	
    	/**
    	 * 添加用户信息
    	 * @param user
    	 * @throws Exception
    	 */
    	public void addUser(User user) throws Exception;
    	
    	/**
    	 * 查找用户，返回一个User对象，例如欢迎你 xxx就需要用到返回user对象
    	 * @param user
    	 * @return
    	 * @throws Exception
    	 */
    	public User findUser(User user) throws Exception;
    	
    	/**
    	 * 根据用户名查找数据库是否存在
    	 * @param name
    	 * @return
    	 * @throws Exception
    	 */
    	public boolean findUserByName(String name) throws Exception;
    }

2.dao.impl实现具体方法

package com.anthony.dao.impl;
    
    import java.sql.Connection;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.text.SimpleDateFormat;
    
    import com.anthony.dao.UserDao;
    import com.anthony.domain.User;
    import com.anthony.utils.DBUtils;
    
    public class UserDaoImpl implements UserDao {
    	
    	public void addUser(User user) throws Exception {
    		Connection conn = null;
    		PreparedStatement ps = null;
    		
    		try {
    			conn = DBUtils.getConnection();
    			ps = conn.prepareStatement("INSERT INTO users(username,password,email,birthday) VALUES(?,?,?,?)");
    			ps.setString(1, user.getUsername());
    			ps.setString(2, user.getPassword());
    			ps.setString(3, user.getEmail());
    			SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    			String date = sdf.format(user.getBirthday());
    			ps.setString(4, date);
    			//执行sql语句,这里是注册，插入数据
    			int i = ps.executeUpdate();
    		} catch (Exception e) {
    			e.printStackTrace();
    		}finally {
    			DBUtils.close(conn, ps, null);
    		}
    		
    	}
    
    	
    	public User findUser(User user) throws Exception {
    		Connection conn = null;
    		PreparedStatement ps = null;
    		ResultSet rs = null;
    		User u = null;
    		
    		try {
    			conn = DBUtils.getConnection();
    			ps = conn.prepareStatement("SELECT * FROM users WHERE username=? AND PASSWORD=?");
    			ps.setString(1, user.getUsername());
    			ps.setString(2, user.getPassword());
    			rs = ps.executeQuery();
    			if(rs.next()) {
    				u = new User();
    				u.setId(rs.getInt(1));
    				u.setUsername(rs.getString(2));
    				u.setPassword(rs.getString(3));
    				u.setEmail(rs.getString(4));
    				u.setBirthday(rs.getDate(5));
    			}
    		} catch (Exception e) {
    			e.printStackTrace();
    		}finally{
    			DBUtils.close(conn, ps, rs);
    		}
    		return u;
    	}
    
    
    	public boolean findUserByName(String name) throws Exception {
    		Connection conn = null;
    		PreparedStatement ps = null;
    		ResultSet rs = null;
    		
    		try {
    			conn = DBUtils.getConnection();
    			ps = conn.prepareStatement("SELECT * FROM users WHERE username=?");
    			ps.setString(1, name);
    			rs = ps.executeQuery();
    			//查到了，返回true
    			if(rs.next()) {
    				return true;
    			}
    		} catch (Exception e) {
    			e.printStackTrace();
    		}finally {
    			DBUtils.close(conn, ps, rs);
    		}
    		
    		return false;
    	}
    
    }

3.在UserService接口中添加方法

这里接着前面代码，新增下面代码

/**
    	 * 根据用户名查找用户是否存在
    	 * @param name
    	 * @return
    	 * @throws UserExistException
    	 */
    	public boolean findUserByName(String name) throws UserExistException;

这里用到一个自定义异常类，所以下面我们要在exception包下新建这个异常类

4.自定义一个异常类

package com.anthony.exception;
    
    public class UserExistException extends Exception {
    
    	public UserExistException() {
    		super();
    	}
    
    	public UserExistException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
    		super(message, cause, enableSuppression, writableStackTrace);
    	}
    
    	public UserExistException(String message, Throwable cause) {
    		super(message, cause);
    	}
    
    	public UserExistException(String message) {
    		super(message);
    	}
    
    	public UserExistException(Throwable cause) {
    		super(cause);
    	}
    	
    }

5. service层具体方法实现

public boolean findUserByName(String name) throws UserExistException {
    		boolean b = false;
    		try {
    			b = userDao.findUserByName(name);
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    		if(b) {
    			throw new UserExistException("用户名已存在！");
    		}
    		return b;
    	}

7.RegServlet.java代码更改如下

package com.anthony.web.servlet;
    
    import java.io.IOException;
    import java.util.Date;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import org.apache.commons.beanutils.BeanUtils;
    import org.apache.commons.beanutils.ConvertUtils;
    import org.apache.commons.beanutils.locale.converters.DateLocaleConverter;
    
    import com.anthony.domain.User;
    import com.anthony.domain.UserForm;
    import com.anthony.exception.UserExistException;
    import com.anthony.service.UserService;
    import com.anthony.service.impl.UserServiceImpl;
    
    
    public class RegServlet extends HttpServlet {
    
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		req.setCharacterEncoding("UTF-8");
    		resp.setContentType("text/html;charset=UTF-8");
    		//获取表单数据
    		UserForm uf = new UserForm();
    		try {
    			BeanUtils.populate(uf, req.getParameterMap());
    		} catch (Exception e1) {
    			e1.printStackTrace();
    		}
    		
    		if(!uf.validate()) { //如果msg map集合不为空，说明输入条件不符合要求
    			req.setAttribute("uf", uf);
    			req.getRequestDispatcher("/register.jsp").forward(req, resp);
    			return; //出错，不需要往下走注册流程，所以这里需要return空来终止代码往下执行
    		}
    		
    		User user = new User();
    		try {
    			//解决日期是字符串的异常
    			ConvertUtils.register(new DateLocaleConverter(), Date.class);
    			BeanUtils.populate(user, req.getParameterMap());
    			//调用业务层方法/逻辑
    			UserService us = new UserServiceImpl();
    			//注册之前判断用户是否存在
    			us.findUserByName(user.getUsername());
    			us.register(user);
    		} catch (UserExistException e1) {
    			req.setAttribute("error", "用户名已存在");
    			req.getRequestDispatcher("/register.jsp").forward(req, resp);
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    		
    		//分发转向
    		resp.getWriter().write("注册成功，2秒之后跳转到主页");
    		resp.setHeader("refresh", "2;url="+req.getContextPath()+"/index.jsp");
    	}
    
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req,resp);
    	}
    	
    	
    
    }

8.register.jsp

添加显示错误消息“用户名已存在”

<%@ page language="java" contentType="text/html; charset=UTF-8"
        pageEncoding="UTF-8"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>注册</title>
    </head>
    <body>
    	<form action="${pageContext.request.contextPath}/servlet/regServlet" method="post">
    		用户名：<input type="text" name="username" value="${uf.username}"/>${uf.msg.username}${error}<br/>
    		密码：<input type="password" name="password"/>${uf.msg.password}<br/>
    		确认密码：<input type="password" name="repassword"/>${uf.msg.repassword}<br/>
    		邮箱：<input type="text" name="email" value="${uf.email}"/>${uf.msg.email}<br/>
    		生日：<input type="text" name="birthday" value="${uf.birthday}"/>${uf.msg.birthday}<br/>
    		<input type="submit" value="注册">
    	</form>
    </body>
    </html>

测试效果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTE1NDE5NDY_size_16_color_FFFFFF_t_70]: /images/20220125/117ae6a1d6224320a59c2504a1602e14.png