用spj+MySQL+servlet+dao实现增删查改的简单代码

以下是使用SPJ（Spring+JPA）、MySQL数据库、Servlet和DAO实现增删查改的简单代码示例：

Student.java（学生实体类）

@Entity
@Table(name = "student")
public class Student {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private Integer age;
    private Float score;

    // getter和setter方法
}

StudentDao.java（学生DAO接口）

public interface StudentDao {
    List<Student> findAll();
    Student findById(Long id);
    void save(Student student);
    void update(Student student);
    void delete(Student student);
}

StudentDaoImpl.java（学生DAO实现类）

@Repository
public class StudentDaoImpl implements StudentDao {
    @PersistenceContext
    private EntityManager entityManager;

    @Override
    public List<Student> findAll() {
        return entityManager.createQuery("SELECT s FROM Student s", Student.class).getResultList();
    }

    @Override
    public Student findById(Long id) {
        return entityManager.find(Student.class, id);
    }

    @Override
    public void save(Student student) {
        entityManager.persist(student);
    }

    @Override
    public void update(Student student) {
        entityManager.merge(student);
    }

    @Override
    public void delete(Student student) {
        entityManager.remove(student);
    }
}

StudentServlet.java（学生Servlet）

@WebServlet("/student/*")
public class StudentServlet extends HttpServlet {
    private StudentDao studentDao;

    @Override
    public void init() throws ServletException {
        super.init();
        studentDao = new StudentDaoImpl();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String pathInfo = request.getPathInfo();
        if (pathInfo == null || pathInfo.equals("/")) {
            List<Student> students = studentDao.findAll();
            request.setAttribute("students", students);
            request.getRequestDispatcher("/WEB-INF/views/student/list.jsp").forward(request, response);
        } else if (pathInfo.equals("/add")) {
            request.getRequestDispatcher("/WEB-INF/views/student/add.jsp").forward(request, response);
        } else if (pathInfo.matches("/\\d+")) {
            Long id = Long.parseLong(pathInfo.substring(1));
            Student student = studentDao.findById(id);
            if (student != null) {
                request.setAttribute("student", student);
                request.getRequestDispatcher("/WEB-INF/views/student/edit.jsp").forward(request, response);
            } else {
                response.sendError(HttpServletResponse.SC_NOT_FOUND);
            }
        } else {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST);
        }
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String pathInfo = request.getPathInfo();
        if (pathInfo == null || pathInfo.equals("/")) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST);
        } else if (pathInfo.equals("/add")) {
            String name = request.getParameter("name");
            Integer age = Integer.parseInt(request.getParameter("age"));
            Float score = Float.parseFloat(request.getParameter("score"));
            Student student = new Student();
            student.setName(name);
            student.setAge(age);
            student.setScore(score);
            studentDao.save(student);
            response.sendRedirect(request.getContextPath() + "/student/");
        } else if (pathInfo.matches("/\\d+")) {
            Long id = Long.parseLong(pathInfo.substring(1));
            Student student = studentDao.findById(id);
            if (student != null) {
                String name = request.getParameter("name");
                Integer age = Integer.parseInt(request.getParameter("age"));
                Float score = Float.parseFloat(request.getParameter("score"));
                student.setName(name);
                student.setAge(age);
                student.setScore(score);
                studentDao.update(student);
                response.sendRedirect(request.getContextPath() + "/student/");
            } else {
                response.sendError(HttpServletResponse.SC_NOT_FOUND);
            }
        } else {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST);
        }
    }

    @Override
    protected void doDelete(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String pathInfo = request.getPathInfo();
        if (pathInfo == null || pathInfo.equals("/")) {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST);
        } else if (pathInfo.matches("/\\d+")) {
            Long id = Long.parseLong(pathInfo.substring(1));
            Student student = studentDao.findById(id);
            if (student != null) {
                studentDao.delete(student);
                response.setStatus(HttpServletResponse.SC_NO_CONTENT);
            } else {
                response.sendError(HttpServletResponse.SC_NOT_FOUND);
            }
        } else {
            response.sendError(HttpServletResponse.SC_BAD_REQUEST);
        }
    }
}

list.jsp（学生列表页面）

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>学生管理</title>
</head>
<body>
    <h1>学生管理</h1>
    <table border="1">
        <thead>
            <tr>
                <th>姓名</th>
                <th>