In Java, CRUD (Create, Read, Update, Delete) operations can be implemented in Servlets to interact with a database or another data source. Servlets can act as controllers that receive HTTP requests, process them, and send back responses. Here's an example of a simple Servlet that implements CRUD operations using JDBC:

import java.io.IOException;
import java.sql.*;
import javax.servlet.ServletException;
import javax.servlet.http.*;

public class StudentServlet extends HttpServlet {
    private Connection connection;

    @Override
    public void init() throws ServletException {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "username", "password");
        } catch (ClassNotFoundException | SQLException e) {
            throw new ServletException(e);
        }
    }

    @Override
    public void destroy() {
        try {
            if (connection != null) {
                connection.close();
            }
        } catch (SQLException e) {
            // Ignore
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            String action = request.getParameter("action");
            if ("list".equals(action)) {
                listStudents(request, response);
            } else if ("edit".equals(action)) {
                showEditForm(request, response);
            } else if ("delete".equals(action)) {
                deleteStudent(request, response);
            } else {
                response.sendError(HttpServletResponse.SC_BAD_REQUEST);
            }
        } catch (SQLException e) {
            throw new ServletException(e);
        }
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            String action = request.getParameter("action");
            if ("create".equals(action)) {
                createStudent(request, response);
            } else if ("update".equals(action)) {
                updateStudent(request, response);
            } else {
                response.sendError(HttpServletResponse.SC_BAD_REQUEST);
            }
        } catch (SQLException e) {
            throw new ServletException(e);
        }
    }

    private void listStudents(HttpServletRequest request, HttpServletResponse response) throws SQLException, ServletException, IOException {
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("SELECT * FROM students");
        request.setAttribute("students", resultSet);
        request.getRequestDispatcher("list.jsp").forward(request, response);
    }

    private void showEditForm(HttpServletRequest request, HttpServletResponse response) throws SQLException, ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        PreparedStatement statement = connection.prepareStatement("SELECT * FROM students WHERE id = ?");
        statement.setInt(1, id);
        ResultSet resultSet = statement.executeQuery();
        if (resultSet.next()) {
            request.setAttribute("student", resultSet);
            request.getRequestDispatcher("edit.jsp").forward(request, response);
        } else {
            response.sendError(HttpServletResponse.SC_NOT_FOUND);
        }
    }

    private void createStudent(HttpServletRequest request, HttpServletResponse response) throws SQLException, ServletException, IOException {
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        PreparedStatement statement = connection.prepareStatement("INSERT INTO students (name, age) VALUES (?, ?)");
        statement.setString(1, name);
        statement.setInt(2, age);
        statement.executeUpdate();
        response.sendRedirect("student?action=list");
    }

    private void updateStudent(HttpServletRequest request, HttpServletResponse response) throws SQLException, ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        String name = request.getParameter("name");
        int age = Integer.parseInt(request.getParameter("age"));
        PreparedStatement statement = connection.prepareStatement("UPDATE students SET name = ?, age = ? WHERE id = ?");
        statement.setString(1, name);
        statement.setInt(2, age);
        statement.setInt(3, id