写一下javaweb学生信息管理系统的servlet类

以下是一个简单的学生信息管理系统的Servlet类示例：

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/student")
public class StudentServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    
    private List<Student> students;
    
    public StudentServlet() {
        super();
        students = new ArrayList<>();
    }

    protected 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":
                showAddForm(request, response);
                break;
            case "edit":
                showEditForm(request, response);
                break;
            case "delete":
                deleteStudent(request, response);
                break;
            default:
                listStudents(request, response);
                break;
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String action = request.getParameter("action");
        
        if (action == null) {
            action = "list";
        }
        
        switch (action) {
            case "add":
                addStudent(request, response);
                break;
            case "edit":
                updateStudent(request, response);
                break;
            default:
                listStudents(request, response);
                break;
        }
    }
    
    private void listStudents(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setAttribute("students", students);
        request.getRequestDispatcher("list.jsp").forward(request, response);
    }
    
    private void showAddForm(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.getRequestDispatcher("add.jsp").forward(request, response);
    }
    
    private void showEditForm(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        Student student = getStudentById(id);
        
        if(student != null) {
            request.setAttribute("student", student);
            request.getRequestDispatcher("edit.jsp").forward(request, response);
        } else {
            response.sendRedirect("student");
        }
    }
    
    private void addStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        
        Student student = new Student(name, age);
        students.add(student);
        
        response.sendRedirect("student");
    }
    
    private void updateStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        Student student = getStudentById(id);
        
        if(student != null) {
            String name = request.getParameter("name");
            int age = Integer.parseInt(request.getParameter("age"));
            
            student.setName(name);
            student.setAge(age);
            
            response.sendRedirect("student");
        } else {
            response.sendRedirect("student");
        }
    }
    
    private void deleteStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        Student student = getStudentById(id);
        
        if(student != null) {
            students.remove(student);
        }
        
        response.sendRedirect("student");
    }
    
    private Student getStudentById(int id) {
        for(Student student : students) {
            if(student.getId() == id) {
                return student;
            }
        }
        
        return null;
    }
}

上述代码是一个基本的学生信息管理系统的Servlet类，包含了添加、编辑、删除和显示学生列表的功能。具体的页面逻辑可以通过JSP页面实现，例如list.jsp用于显示学生列表，add.jsp用于添加学生，edit.jsp用于编辑学生信息。