1 目标效果预览
1.1 展示学生信息时，多添加一列展示所属班级（班级表是另一个表）
1.2 添加学生信息时，多一行班级选择（班级表是另一个表）
1.3 点击“编辑”后，修改学生信息时，查询其所属班级并默认选中
2 学生表和班级表连接查询并显示(Value Object)
重新封装要展示的信息为一个类，并编写相应的Servlet、Service、Dao
StudentBanjiVO
/*
* 适度编码益脑，沉迷编码伤身，合理安排时间，享受快乐生活。
* Copyright @TangXJ
* Created by TangXJ
* Created&Used date: 2024/4/8 下午3:13 ~ 2024/4/8 下午3:18
* Modified date: 2024/4/8 下午3:14
*/
package com.sdust.web.pojo.vo;
//VO:Value Object
public class StudentBanjiVO {
private Integer id;
private String name;
private Integer age;
private String gender;
private Integer banjiId;
private String banjiName;
public StudentBanjiVO() {
}
public StudentBanjiVO(Integer id, String name, Integer age, String gender, Integer banjiId, String banjiName) {
this.id = id;
this.name = name;
this.age = age;
this.gender = gender;
this.banjiId = banjiId;
this.banjiName = banjiName;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public Integer getBanjiId() {
return banjiId;
}
public void setBanjiId(Integer banjiId) {
this.banjiId = banjiId;
}
public String getBanjiName() {
return banjiName;
}
public void setBanjiName(String banjiName) {
this.banjiName = banjiName;
}
@Override
public String toString() {
return "StudentBanjiVO{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
", gender='" + gender + '\'' +
", banjiId=" + banjiId +
", banjiName='" + banjiName + '\'' +
'}';
}
}
连接查询
学点儿数据库_Day11_多表、等值连接、内连接、模糊查找
SELECT s.id,s.`name`,s.age,s.gender,b.id as banji_id,b.`name` AS banji_name
FROM student AS s INNER JOIN banji AS b
ON s.banji_id=b.id
ORDER BY s.id
LIMIT 0,5
StudentDaoImply：
@Override
public List<StudentBanjiVO> selectByPage(int offset, Integer pageSize) {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
List<StudentBanjiVO> list = new ArrayList<>();
try {
connection = JDBCUtil.getConnection();
String sql = "SELECT s.id,s.`name`,s.age,s.gender,b.id as banji_id,b.`name` AS banji_name\n" +
"FROM student AS s INNER JOIN banji AS b\n" +
"ON s.banji_id=b.id\n" +
"ORDER BY s.id\n" +
"LIMIT ?,? ";
statement = connection.prepareStatement(sql);
statement.setInt(1, offset);
statement.setInt(2, pageSize);
System.out.println(statement);
resultSet = statement.executeQuery();
while (resultSet.next()) {
int id = resultSet.getInt("id");
String name = resultSet.getString("name");
int age = resultSet.getInt("age");
String gender = resultSet.getString("gender");
int banjiId = resultSet.getInt("banji_id");
String banjiName = resultSet.getString("banji_name");
StudentBanjiVO student = new StudentBanjiVO(id, name, age, gender, banjiId, banjiName);
list.add(student);
}
} catch (SQLException e) {
throw new RuntimeException(e);
}
return list;
}
3 带查询班级表的学生信息添加
写一套班级的servlet、service、dao，然后在StudentServlet里边的toUpdate调用一下班级的查询service，一起发送到student_add.jsp即可
这就是三层架构、解耦合的“威力”
private void updateQuery(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("StudentServlet.updateQuery");
String queryId = req.getParameter("id");
Student student = studentService.selectById(Integer.parseInt(queryId));
List<Banji> banjiList = banjiService.selectAll();//1.第一句
//把数据放到req里面
req.setAttribute("student", student);
req.setAttribute("banjiList", banjiList);//2.第二句
//转发到student_list.jsp页面进行展示
req.getRequestDispatcher("student_update.jsp").forward(req, resp);
}
student_add.jsp：
<%@ page import="java.util.List" %>
<%@ page import="com.sdust.web.pojo.entity.Banji" %><%--
~ 适度编码益脑，沉迷编码伤身，合理安排时间，享受快乐生活。
~ Copyright @TangXJ
~ Created by TangXJ
~ Created&Used date: 2024/4/3 下午2:21 ~ 2024/4/8 下午4:00
~ Modified date: 2024/4/8 下午4:00
--%>
<%--
Created by IntelliJ IDEA.
User: TangXJ
Date: 2024/4/3
Time: 14:21
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<%--<form action="/student?method=add" method="get">--%>
<%--默认就是get ?method=就是get方法传参 会被覆盖 所以form表单一般不用--%>
<%
List<Banji> banjiList = (List<Banji>) request.getAttribute("banjiList");
%>
<form action="/student?method=add" method="post"><%--默认就是get ?method=就是get方法传参 会被覆盖 所以form表单一般不用--%>
姓名:<input type="text" name="name"><br>
年龄:<input type="text" name="age"><br>
性别:<input type="text" name="gender"><br>
班级:<select name="banjiId">
<%
for (Banji banji : banjiList) {
%>
<option value="<%=banji.getId()%>"><%=banji.getName()%></option>
<%
}
%>
</select><br>
<input type="submit" value="添加">
</form>
</body>
</html>
4 带查询班级并回显的学生信息修改
文章来源：https://www.toymoban.com/news/detail-850540.html
<select name="class">
<%
// 假设classList是从Servlet传递过来的班级列表，每个班级对象包含id和name属性
for (ClassInfo classInfo : classList) {
// 根据学生ID和班级ID是否一致来确定哪个选项应该被选中
String selected = (student.getId() == classInfo.getId()) ? "selected" : "";
%>
<option value="<%= classInfo.getId() %>" <%= selected %>><%= classInfo.getName() %></option>
<%
}
%>
</select>
student_update.jsp：文章来源地址https://www.toymoban.com/news/detail-850540.html
<%@ page import="com.sdust.web.pojo.entity.Student" %>
<%@ page import="java.util.List" %>
<%@ page import="com.sdust.web.pojo.entity.Banji" %><%--
~ 适度编码益脑，沉迷编码伤身，合理安排时间，享受快乐生活。
~ Copyright @TangXJ
~ Created by TangXJ
~ Created&Used date: 2024/4/3 下午2:54 ~ 2024/4/8 下午4:19
~ Modified date: 2024/4/8 下午4:19
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<%
//JSP脚本，这里面可以任意写java代码
//request、response:JSP内置对象
Student student = (Student) request.getAttribute("student");
List<Banji> banjiList = (List<Banji>) request.getAttribute("banjiList");
System.out.println(student);
System.out.println(banjiList);
%>
<%--<form action="/student?method=update&id=<%=student.getId()%>" method="post">--%><%--默认就是get ?method=就是get方法传参 会被覆盖 所以form表单一般不用--%>
<form action="/student?method=update" method="post" onsubmit="return update_confirm()"><%--默认就是get ?method=就是get方法传参 会被覆盖 所以form表单一般不用--%>
<input type="hidden" name="id" value="<%=student.getId()%>"/>
<%--<input type="hidden" name="id" value="<%=student.getId()%>"/>--%><%--readonly 可以删掉F12！！ 以后学后端验证--%>
姓名:<input type="text" name="name" value="<%=student.getName()%>"><br>
年龄:<input type="text" name="age" value="<%=student.getAge()%>"><br>
性别:<input type="text" name="gender" value="<%=student.getGender()%>"><br>
班级:<select name="banjiId">
<%
for (Banji banji : banjiList) {
String selected = (student.getBanjiId() == banji.getId()) ? "selected" : "";
%>
<option value="<%=banji.getId()%>" <%=selected%>><%=banji.getName()%></option>
<%
}
%>
</select><br>
<input type="submit" value="更新">
</form>
<script>
function update_confirm(){
return confirm("您确认要更新吗？");
}
</script>
</body>
</html>
到了这里，关于Day19_学点儿JavaEE_学生表和班级表连接查询并显示、带查询班级表的学生信息添加、带查询班级并回显的学生信息修改的文章就介绍完了。如果您还想了解更多内容，请在右上角搜索TOY模板网以前的文章或继续浏览下面的相关文章，希望大家以后多多支持TOY模板网！
