用javaweb写一下学生信息管理系统增删改查servlet类代码

下面是一个简单的学生信息管理系统的增删改查的Servlet类代码示例：

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("/StudentServlet")
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":
                addStudent(request, response);
                break;
            case "edit":
                editStudent(request, response);
                break;
            case "update":
                updateStudent(request, response);
                break;
            case "delete":
                deleteStudent(request, response);
                break;
            default:
                listStudents(request, response);
                break;
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
    
    private void listStudents(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setAttribute("students", students);
        request.getRequestDispatcher("list-students.jsp").forward(request, response);
    }
    
    private void addStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        String gender = request.getParameter("gender");
        
        Student student = new Student(name, age, gender);
        students.add(student);
        
        response.sendRedirect("StudentServlet");
    }
    
    private void editStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        Student student = students.get(id);
        
        request.setAttribute("student", student);
        request.getRequestDispatcher("edit-student.jsp").forward(request, response);
    }
    
    private void updateStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        String gender = request.getParameter("gender");
        
        Student student = students.get(id);
        student.setName(name);
        student.setAge(age);
        student.setGender(gender);
        
        response.sendRedirect("StudentServlet");
    }
    
    private void deleteStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        students.remove(id);
        
        response.sendRedirect("StudentServlet");
    }
}

以上代码示例中，每个功能对应一个方法，通过判断action参数来调用相应的方法。listStudents方法用于展示学生列表，addStudent方法用于添加学生，editStudent方法用于编辑学生信息，updateStudent方法用于更新学生信息，deleteStudent方法用于删除学生信息。

注意：上述示例代码仅供参考，具体实现还需要根据具体的业务逻辑进行修改和完善。