起源
在要实现管理员对学员的修改时，点击“修改”进入修改界面后，修改界面中如果和注册界面就需要让用户把不需要修改的信息也重新再写一遍，很麻烦也很容易出错，因此就思考能否在进入界面之后就显示已注册全部信息，这样就只需要修改用户想要修改的界面就可以了。于是查找一些资料后自己用以下代码实现了表单回显功能，不一定是最简洁的实现，如果有需要改进的欢迎各位评论赐教~
什么是表单回显
所谓“表单回显”就是说在进入一个新界面时，会将后端已有的数据显示到界面上。比如需要修改用户信息时，点击修改按钮后跳转到修改界面，修改界面中的用户信息会显示在界面上，这个就是表单回显
实现表单回显思想
点击功能按键后–>获取对应用户的信息返回给后端（增设一个转发servlet）–>转发servlet中将获取到的用户数据封装之后转发到功能界面–>功能界面中获取转发而来的数据后显示从而实现回显功能
具体实现（以修改用户信息功能为例）
修改功能按键所在界面
<%@ page import="com.lagou.bean.Manager" %>
<%@ page import="com.lagou.service.ManagerService" %>
<%@ page import="com.lagou.bean.Student" %>
<%@ page import="java.util.Set" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page errorPage="error.jsp" %>
<html>
<head>
<title>管理员界面</title>
<link rel="stylesheet" href="./WebContent/css/bootstrap.min.css">
</head>
<body>
<h1 align="center">登录成功，欢迎<%= ((Manager)session.getAttribute("manager")).getUsername() %>使用学生管理系统</h1>
<%
//获取当前登录的管理员id
int mid = ((Manager) session.getAttribute("manager")).getMid();
//登录成功之后该管理员信息将是在整个服务器上所有用户（servlet）之间共享
application.setAttribute("mid", mid);
%>
<div style="float: left">
<form action="search", method="get">
<div align="center">
请输入要查询的学生姓名：<input type="text" name="username">
<input type="submit" value="查询" class="btn btn-primary">
</div>
</form>
</div>
<div style="float: left">
<a href="insert.jsp"><button class="btn btn-success">添加</button></a>
</div>
<table class="table table-hover table-responsive">
<caption>学生信息</caption>
<thead>
<tr>
<th>学号</th>
<th>姓名</th>
<th>性别</th>
<th>出生日期</th>
<th>邮箱</th>
<th>备注</th>
<th>操作</th>
</tr>
</thead>
<tbody>
<%
//获取管理员的id并发送给servlet
ManagerService managerService = new ManagerService();
//执行查询全部学生
Set<Student> studentsAll = managerService.searchAllStudent(mid);
// System.out.println("studentsAll：" + studentsAll);
//执行根据姓名查询学生
Set<Student> students = (Set<Student>) request.getAttribute("students");
System.out.println(students);
//判断是否为搜索单个学生
if (students != null) {
for (Student s : students) {
out.print("<tr>" + "<td>" + s.getsNum() + "</td>" +
"<td>" + s.getStuName() + "</td>" +
"<td>" + s.getGender() + "</td>" +
"<td>" + s.getBirthday() + "</td>" +
"<td>" + s.getEmail() + "</td>" +
"<td>" + s.getRemark() + "</td>" +
"<td>" +
"<a href=\"updateTransfer?sNum="
+ s.getsNum() + "&stuName=" + s.getStuName() + "&gender=" + s.getGender() + "&birthday=" + s.getBirthday()
+ "&email=" + s.getEmail() + "&remark=" + s.getRemark()
+ "\" class=\"btn btn-warning\">修改</a> " +
"<a href=\"deleteStu?sNum=" + s.getsNum() + "\" class=\"btn btn-danger\">删除</a>" +
"</td>" +
"</tr>");
}
} else {
for (Student s : studentsAll) {
out.print("<tr>" + "<td>" + s.getsNum() + "</td>" +
"<td>" + s.getStuName() + "</td>" +
"<td>" + s.getGender() + "</td>" +
"<td>" + s.getBirthday() + "</td>" +
"<td>" + s.getEmail() + "</td>" +
"<td>" + s.getRemark() + "</td>" +
"<td>" +
"<a href=\"updateTransfer?sNum="
+ s.getsNum() + "&stuName=" + s.getStuName() + "&gender=" + s.getGender() + "&birthday=" + s.getBirthday()
+ "&email=" + s.getEmail() + "&remark=" + s.getRemark()
+ "\" class=\"btn btn-warning\">修改</a> " +
"<a href=\"deleteStu?sNum=" + s.getsNum() + "\" class=\"btn btn-danger\">删除</a>" +
"</td>" +
"</tr>");
}
}
%>
</tbody>
</table>
</body>
</html>
点击对应学员修改按键后，跳转到一个转发servlet
"<a href=\"updateTransfer?sNum="
+ s.getsNum() + "&stuName=" + s.getStuName() + "&gender=" + s.getGender() + "&birthday=" + s.getBirthday()
+ "&email=" + s.getEmail() + "&remark=" + s.getRemark()
+ "\" class=\"btn btn-warning\">修改</a>
转发servlet代码
import com.lagou.bean.Student;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
@WebServlet(name = "UpdateTransferServlet", urlPatterns = "/updateTransfer")
public class UpdateTransferServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1、获取前端传来的学号
int sNum = Integer.parseInt(request.getParameter("sNum"));
System.out.println("前端传来的学号：" + sNum);
String stuName = request.getParameter("stuName");
System.out.println("前端传来的姓名：" + stuName);
String gender = request.getParameter("gender");
System.out.println("前端传来的性别：" + gender);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Date birthday = null;
try {
birthday = sdf.parse(request.getParameter("birthday"));
} catch (ParseException e) {
e.printStackTrace();
}
System.out.println("前端传来的生日：" + birthday);
String email = request.getParameter("email");
System.out.println("前端传来的邮箱：" + email);
String remark = request.getParameter("remark");
System.out.println("前端传来的备注：" + remark);
//2、将信息封装到对象中
Student student = new Student(sNum, stuName, gender, birthday, email, remark);
//2、转发到修改学员jsp
request.setAttribute("student", student);
RequestDispatcher requestDispatcher = request.getRequestDispatcher("update.jsp");
requestDispatcher.forward(request, response);
}
}
跳转到update.jsp界面，update.jsp界面中获取学员数据信息，实现回显功能
<%@ page import="com.lagou.bean.Student" %>
<%@ page import="java.util.Date" %>
<%@ page import="java.text.SimpleDateFormat" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>修改学员信息主页</title>
<link rel="stylesheet" href="./WebContent/css/bootstrap.min.css">
<script src="./WebContent/js/jquery-3.4.1.min.js"></script>
</head>
<body style="padding: 100px">
<h1 align="center">请输入修改后的学员信息</h1>
<form action="updateStu" method="get">
<%
int sNum = ((Student) request.getAttribute("student")).getsNum();
request.setAttribute("sNum", sNum);
%>
<div class="form-group" style="align-content: center; width: 30%">
<label>姓名</label>
<input type="text" name="stuName" class="form-control" placeholder="请输入姓名" value="<%= ((Student)request.getAttribute("student")).getStuName() %>">
</div>
<div class="form-group" style="align-content: center">
<label>性别</label><br>
<%
//获取当前学员的性别后在对应性别选项上设置checked
String gender = ((Student) request.getAttribute("student")).getGender();
System.out.println("update.jsp中的性别：" + gender);
%>
<input type="radio" name="gender" value="男" <%if(gender.equals("男")) {%> checked="checked" <%}%> >男
<input type="radio" name="gender" value="女" <%if(gender.equals("女")) {%> checked="checked" <%}%>>女
</div>
<div class="form-group" style="align-content: center">
<label>出生日期</label><br>
<%--注意：date类型的input要想显示出来，格式必须是yyyy-MM-dd，就连2019-4-1这样都不行，必须是2019-04-01，否则没有效果--%>
<%
Date birth = ((Student) request.getAttribute("student")).getBirthday();
//将Date类型转换为String类型就可以变成yyyy-MM-dd的格式
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String birthday = sdf.format(birth);
System.out.println("update.jsp中转换后的生日：" + birthday);
%>
<input type="date" id="date" name="birthday" placeholder="请输入出生日期" value="<%= birthday %>">
</div>
<div class="form-group" style="align-content: center">
<label>邮箱</label><br>
<input type="email" name="email" placeholder="请输入邮箱" value="<%= ((Student)request.getAttribute("student")).getEmail() %>">
</div>
<div class="form-group" style="align-content: center">
<label>备注</label><br>
<textarea name="remark" placeholder="请输入备注" cols="30" rows="5"><%= ((Student)request.getAttribute("student")).getRemark() %></textarea>
</div>
<input type="reset" class="btn btn-danger" value="重置">
<input type="submit" class="btn btn-success" value="提交">
</form>
</body>
</html>
之后就是表单提交数据到后端进行更新修改，略
实现过程一些注意点
- 主要要注意一下表单回显获取数据时不同类型的input怎么显示数据的问题
- type为text、email、password等文本类标签直接将获取到的数据放入value属性中即可
- type为radio、checkbox或者<select>标签等选择样式：要结合判断语句对获取数据进行判断，根据获取数据的值设置对应选项为选中效果。如：
<div class="form-group" style="align-content: center">
<label>性别</label><br>
<%
//获取当前学员的性别后在对应性别选项上设置checked
String gender = ((Student) request.getAttribute("student")).getGender();
System.out.println("update.jsp中的性别：" + gender);
%>
<input type="radio" name="gender" value="男" <%if(gender.equals("男")) {%> checked="checked" <%}%> >男
<input type="radio" name="gender" value="女" <%if(gender.equals("女")) {%> checked="checked" <%}%>>女
</div>
3.type为date：一定要注意格式
所以必须要将获取到的数据转为yyyy-MM-dd格式才行。如：
<div class="form-group" style="align-content: center">
<label>出生日期</label><br>
<%--注意：date类型的input要想显示出来，格式必须是yyyy-MM-dd，就连2019-4-1这样都不行，必须是2019-04-01，否则没有效果--%>
<%
Date birth = ((Student) request.getAttribute("student")).getBirthday();
//将Date类型转换为String类型就可以变成yyyy-MM-dd的格式
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String birthday = sdf.format(birth);
System.out.println("update.jsp中转换后的生日：" + birthday);
%>
<input type="date" id="date" name="birthday" placeholder="请输入出生日期" value="<%= birthday %>">
</div>
