写出javaweb代码

以下是使用 Java Web 技术和 MySQL 数据库的示例代码，基于 Servlet 和 JSP：

1. 配置数据库连接

在 `WEB-INF` 目录下创建一个名为 `db.properties` 的文件，并添加以下内容：

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/your_database_name
jdbc.username=your_database_username
jdbc.password=your_database_password

将 `your_database_name`、`your_database_username` 和 `your_database_password` 替换为您的 MySQL 数据库名称、用户名和密码。

2. 创建 DAO 类

创建一个名为 `StudentDao` 的 Java 类，用于与数据库交互并处理学生信息。以下是该类的示例代码：

import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;

public class StudentDao {
  private Connection connection;

  public StudentDao() {
    try {
      Properties properties = new Properties();
      properties.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("db.properties"));
      Class.forName(properties.getProperty("jdbc.driver"));
      connection = DriverManager.getConnection(
          properties.getProperty("jdbc.url"),
          properties.getProperty("jdbc.username"),
          properties.getProperty("jdbc.password")
      );
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  public List<Student> getAllStudents() {
    List<Student> students = new ArrayList<>();
    try {
      Statement statement = connection.createStatement();
      ResultSet resultSet = statement.executeQuery("SELECT * FROM students");
      while (resultSet.next()) {
        Student student = new Student();
        student.setId(resultSet.getInt("id"));
        student.setName(resultSet.getString("name"));
        student.setEmail(resultSet.getString("email"));
        student.setPhone(resultSet.getString("phone"));
        students.add(student);
      }
    } catch (SQLException e) {
      e.printStackTrace();
    }
    return students;
  }

  public void addStudent(Student student) {
    try {
      PreparedStatement preparedStatement = connection.prepareStatement(
          "INSERT INTO students (name, email, phone) VALUES (?, ?, ?)"
      );
      preparedStatement.setString(1, student.getName());
      preparedStatement.setString(2, student.getEmail());
      preparedStatement.setString(3, student.getPhone());
      preparedStatement.executeUpdate();
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }

  public void updateStudent(Student student) {
    try {
      PreparedStatement preparedStatement = connection.prepareStatement(
          "UPDATE students SET name=?, email=?, phone=? WHERE id=?"
      );
      preparedStatement.setString(1, student.getName());
      preparedStatement.setString(2, student.getEmail());
      preparedStatement.setString(3, student.getPhone());
      preparedStatement.setInt(4, student.getId());
      preparedStatement.executeUpdate();
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }

  public void deleteStudent(int id) {
    try {
      PreparedStatement preparedStatement = connection.prepareStatement(
          "DELETE FROM students WHERE id=?"
      );
      preparedStatement.setInt(1, id);
      preparedStatement.executeUpdate();
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }
}

该类使用 JDBC API 与 MySQL 数据库进行交互。其中 `getAllStudents()` 方法用于获取所有学生信息，`addStudent()` 方法用于添加新学生，`updateStudent()` 方法用于更新学生信息，`deleteStudent()` 方法用于删除学生信息。每个方法都使用预处理语句来执行 SQL 查询和修改。

3. 创建 Servlet 类

创建一个名为 `StudentServlet` 的 Java 类，用于处理学生信息请求。以下是该类的示例代码：

import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class StudentServlet extends HttpServlet {
  private StudentDao studentDao;

  public void init() {
    studentDao = new StudentDao();
  }

  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    String action = request.getParameter("action");
    if (action == null) {
      action = "list";
    }

    switch (action) {
      case "list":
        listStudents(request, response);
        break;
      case "add":
        addStudent(request, response);
        break;
      case "edit":
        editStudent(request, response);
        break;
      case "delete":
        deleteStudent(request, response);
        break;
      default:
        listStudents(request, response);
        break;
    }
  }

  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    doGet(request, response);
  }

  private void listStudents(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    List<Student> students = studentDao.getAllStudents();
    request.setAttribute("students", students);
    request.getRequestDispatcher("student-list.jsp").forward(request, response);
  }

  private void addStudent(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    String name = request.getParameter("name");
    String email = request.getParameter("email");
    String phone = request.getParameter("phone");
    Student student = new Student(name, email, phone);
    studentDao.addStudent(student);
    response.sendRedirect("student?action=list");
  }

  private void editStudent(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    int id = Integer.parseInt(request.getParameter("id"));
    String name = request.getParameter("name");
    String email = request.getParameter("email");
    String phone = request.getParameter("phone");
    Student student = new Student(id, name, email, phone);
    studentDao.updateStudent(student);
    response.sendRedirect("student?action=list");
  }

  private void deleteStudent(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    int id = Integer.parseInt(request.getParameter("id"));
    studentDao.deleteStudent(id);
    response.sendRedirect("student?action=list");
  }
}

该类继承了 `HttpServlet` 类，并覆盖了 `doGet` 和 `doPost` 方法。在 `doGet` 方法中，根据请求参数 `action` 的值调用相应的方法。例如，当 `action` 为 `list` 时，调用 `listStudents()` 方法来获取所有学生信息并将其显示在 JSP 页面上。当 `action` 为 `add` 时，调用 `addStudent()` 方法来添加新学生并重定向到学生列表页面。其他方法（`editStudent()` 和 `deleteStudent()`）类似。

4. 创建 JSP 页面

在 `WebContent` 目录下创建一个名为 `student-list.jsp` 的 JSP 文件，并添加以下内容：

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>学生列表</title>
</head>

<body>
  <h1>学生列表</h1>
  <table>
    <tr>
      <th>ID</th>
      <th>姓名</th>
      <th>邮箱</th>
      <th>电话</th>
      <th>操作</th>
    </tr>
    <c:forEach var="student" items="${students}">
      <tr>
        <td>${student.id}</td>
        <td>${student.name}</td>
        <td>${student.email}</td>
        <td>${student.phone}</td>
        <td>
          <a href="student?action=edit&id=${student.id}">编辑</a>
          <a href="student?action=delete&id=${student.id}">删除</a>
        </td>
      </tr>
    </c:forEach>
  </table>
  <hr>
  <h2>添加学生</h2>
  <form method="post" action="student">
    <input type="hidden" name="action" value="add">
    <label>姓名：<input type="text" name="name"></label>
    <label>邮箱：<input type="text" name="email"></label>
    <label>电话：<input type="text" name="phone"></label>
    <button type="submit">添加</button>
  </form>
</body>
</html>

该 JSP 页面使用 JSTL 标签库来循环显示学生信息。在表格中，每个学生都有一个编辑和删除链接。在页面底部，有一个表单用于添加新学生。该表单将请求方法设置为 `post`，并将表单数据提交到 `StudentServlet`。