前提概要
需要理解的重要概念
-
MVC模式：
- Model（person类）：数据模型
- View（JSP）：显示界面
- Controller（Servlet）：处理业务逻辑
-
请求流程：
浏览器 → Servlet → 数据库 → JSP → 浏览器 -
两种跳转方式：
- 转发（forward）：服务器内部跳转，地址栏不变
- 重定向（redirect）：告诉浏览器重新请求，地址栏变化
-
数据库操作步骤：
加载驱动 → 获取连接 → 创建语句 → 执行SQL → 处理结果 → 关闭连接
代码框架：
一、Person类
Person类：
这个类的作用：
- 就像"用户信息模板"，每个person对象对应数据库中的一条用户记录
- 包含三个属性：
- id：用户唯一标识
- name：用户名
- pwd：密码
- Getter/Setter方法用于外部访问这些私有属性（Java封装的特性）
package com.Person; public class person { private int id; private String name; private String pwd; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPwd() { return pwd; } public void setPwd(String pwd) { this.pwd = pwd; } } -
二、Servlet类
AddServlet类
- 用户访问/add，GET请求会跳转到add.jsp（显示表单）
- 用户提交表单时（POST请求）：
- 接收用户名和密码
- 连接数据库并插入新用户
- 成功后自动跳转到用户列表页
package com.servlet;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.io.IOException;
import java.sql.*;
@WebServlet(name = "AddServlet", urlPatterns = "/add")
public class AddServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.sendRedirect("add.jsp"); // 跳转到添加页面
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
String name = request.getParameter("username");
String pwd = request.getParameter("userpwd");
try {
Class.forName("com.mysql.cj.jdbc.Driver");
Connection connection = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/users?useSSL=false&serverTimezone=UTC", "root", "cjl");
PreparedStatement statement = connection.prepareStatement(
"INSERT INTO person (name, pwd) VALUES (?, ?)");
statement.setString(1, name);
statement.setString(2, pwd);
statement.executeUpdate();
response.sendRedirect("listall"); // 添加成功跳转列表
statement.close();
connection.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}ListAllServlet类：
- 查询数据库获取所有用户
- 把每个用户数据封装成person对象
- 把用户列表存入request（就像把数据装进快递盒）
- 转发到list.jsp显示（快递员把盒子送到JSP）
package com.servlet; import com.Person.person; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.annotation.*; import java.io.IOException; import java.sql.*; import java.util.ArrayList; import java.util.List; @WebServlet(name = "ListAllServlet", urlPatterns = "/listall") public class ListAllServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { try { Class.forName("com.mysql.cj.jdbc.Driver"); Connection connection = DriverManager.getConnection( "jdbc:mysql://localhost:3306/users?useSSL=false&serverTimezone=UTC", "root", "cjl"); Statement statement = connection.createStatement(); ResultSet resultSet = statement.executeQuery("SELECT * FROM person"); // 将数据存入 List<person> List<person> userList = new ArrayList<>(); while (resultSet.next()) { person p = new person(); p.setId(resultSet.getInt("id")); // 确保列名与数据库一致 p.setName(resultSet.getString("name")); p.setPwd(resultSet.getString("pwd")); userList.add(p); } // 关键修复点：将数据存入 request 并转发到 JSP request.setAttribute("userList", userList); request.getRequestDispatcher("/list.jsp").forward(request, response); // 关闭资源 resultSet.close(); statement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); response.getWriter().println("数据库错误，请检查控制台日志"); } } }DeleteServlet类
- 通过URL参数获取要删除的用户id（如/del?id=3）
- 执行数据库删除操作
- 完成后跳回列表页
package com.servlet; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.annotation.*; import java.io.IOException; import java.sql.*; @WebServlet(name = "DeleteServlet", urlPatterns = "/del") public class DeleteServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String id = request.getParameter("id"); try { Class.forName("com.mysql.cj.jdbc.Driver"); Connection connection = DriverManager.getConnection( "jdbc:mysql://localhost:3306/users?useSSL=false&serverTimezone=UTC", "root", "cjl"); PreparedStatement statement = connection.prepareStatement("DELETE FROM person WHERE id=?"); statement.setInt(1, Integer.parseInt(id)); statement.executeUpdate(); response.sendRedirect("listall"); // 直接跳转，不处理失败情况 statement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } } }UpdateServlet类（显示修改页面）：
- 根据id查询要修改的用户
- 把用户数据传给update.jsp显示在表单里
package com.servlet; import com.Person.person; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.annotation.*; import java.io.IOException; import java.sql.*; @WebServlet(name = "UpdateServlet", urlPatterns = "/update") public class UpdateServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String id = request.getParameter("id"); if (id == null || id.isEmpty()) { response.sendRedirect("error.jsp?msg=Invalid+ID"); return; } Connection connection = null; PreparedStatement statement = null; ResultSet resultSet = null; try { Class.forName("com.mysql.cj.jdbc.Driver"); connection = DriverManager.getConnection( "jdbc:mysql://localhost:3306/users?useSSL=false&serverTimezone=UTC", "root", "cjl"); statement = connection.prepareStatement("SELECT * FROM person WHERE id=?"); statement.setInt(1, Integer.parseInt(id)); resultSet = statement.executeQuery(); if (resultSet.next()) { person p = new person(); p.setId(resultSet.getInt("id")); p.setName(resultSet.getString("name")); p.setPwd(resultSet.getString("pwd")); request.setAttribute("user", p); } else { response.sendRedirect("error.jsp?msg=User+not+found"); return; } request.getRequestDispatcher("/update.jsp").forward(request, response); } catch (ClassNotFoundException | SQLException e) { e.printStackTrace(); response.sendRedirect("error.jsp?msg=Database+error"); } finally { try { if (resultSet != null) resultSet.close(); if (statement != null) statement.close(); if (connection != null) connection.close(); } catch (SQLException e) { e.printStackTrace(); } } } }UpdateDoServlet类（处理修改提交）
- 接收修改后的用户名和密码
- 执行数据库更新操作
- 返回列表页
package com.servlet; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.annotation.*; import java.io.IOException; import java.sql.*; @WebServlet(name = "UpdateDoServlet", urlPatterns = "/updateDo") public class UpdateDoServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); String id = request.getParameter("id"); String name = request.getParameter("username"); String pwd = request.getParameter("userpwd"); try { Class.forName("com.mysql.cj.jdbc.Driver"); Connection connection = DriverManager.getConnection( "jdbc:mysql://localhost:3306/users?useSSL=false&serverTimezone=UTC", "root", "cjl"); PreparedStatement statement = connection.prepareStatement( "UPDATE person SET name=?, pwd=? WHERE id=?"); statement.setString(1, name); statement.setString(2, pwd); statement.setInt(3, Integer.parseInt(id)); statement.executeUpdate(); response.sendRedirect("listall"); // 直接跳转列表 statement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } } }Q：为什么修改用户要分成两个Servlet？
A：一个负责显示修改页面（GET），一个处理修改提交（POST），符合单一职责原则
三、JSP
add页面
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>新增用户</title>
</head>
<body>
<h1>新增用户</h1>
<form action="add" method="post">
姓名：<input type="text" name="username"><br>
密码：<input type="password" name="userpwd"><br>
<input type="submit" value="提交">
</form>
</body>
</html>list 页面
<%@ page import="com.Person.person" %>
<%@ page import="java.util.List" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>用户列表</title>
</head>
<body>
<h1>用户列表</h1>
<a href="add">新增用户</a>
<table border="1">
<tr>
<th>ID</th>
<th>姓名</th>
<th>密码</th>
<th>操作</th>
</tr>
<%
List<person> userList = (List<person>) request.getAttribute("userList");
if (userList != null) {
for (person user : userList) {
%>
<tr>
<td><%= user.getId() %></td>
<td><%= user.getName() %></td>
<td><%= user.getPwd() %></td>
<td>
<a href="del?id=<%= user.getId() %>">删除</a>
<a href="update?id=<%= user.getId() %>">修改</a>
</td>
</tr>
<%
}
} else {
%>
<tr>
<td colspan="4">暂无用户数据</td>
</tr>
<% } %>
</table>
</body>
</html>update页面
<%@ page import="com.Person.person" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>修改用户</title>
</head>
<body>
<h1>修改用户信息</h1>
<%person user = (person) request.getAttribute("user");if (user != null) {%>
<form action="updateDo" method="post">
<input type="hidden" name="id" value="<%= user.getId() %>">
姓名：<input type="text" name="username" value="<%= user.getName() %>"><br>
密码：<input type="password" name="userpwd" value="<%= user.getPwd() %>"><br>
<input type="submit" value="提交修改">
</form>
<% } else { %>
<p>错误：用户信息不存在！</p>
<% } %>
</body>
</html>error页面
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>错误页面</title>
</head>
<body>
<h1>错误：<%= request.getParameter("msg") %></h1>
<a href="listall">返回用户列表</a>
</body>
</html>
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