javaee编写一个增删改查

好的，以下是一个简单的 JavaEE 实现增删改查（CRUD）的示例：

首先，创建一个名为 `User` 的 JavaBean，表示一个用户，包含以下属性和方法：

public class User {
    private int id;
    private String name;
    private int age;
    // 省略构造方法和getter/setter方法
    
    // toString方法，用于输出用户信息
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
    }
}

接下来，创建一个 DAO（数据访问对象） 接口 `UserDao`，定义增删改查的方法：

public interface UserDao {
    // 添加用户
    public void addUser(User user);
    
    // 根据ID删除用户
    public void deleteUser(int id);
    
    // 修改用户信息
    public void updateUser(User user);
    
    // 根据ID查询用户信息
    public User getUserById(int id);
    
    // 查询所有用户信息
    public List<User> getAllUsers();
}

然后，创建一个 `UserDaoImpl` 类实现 `UserDao` 接口，使用 JDBC 连接数据库进行数据操作：

public class UserDaoImpl implements UserDao {
    // JDBC连接对象
    private Connection conn;
    
    // 构造方法，获取JDBC连接
    public UserDaoImpl() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "123456");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // 添加用户
    public void addUser(User user) {
        try {
            PreparedStatement ps = conn.prepareStatement("insert into user(name, age) values(?, ?)");
            ps.setString(1, user.getName());
            ps.setInt(2, user.getAge());
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // 根据ID删除用户
    public void deleteUser(int id) {
        try {
            PreparedStatement ps = conn.prepareStatement("delete from user where id = ?");
            ps.setInt(1, id);
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // 修改用户信息
    public void updateUser(User user) {
        try {
            PreparedStatement ps = conn.prepareStatement("update user set name=?, age=? where id=?");
            ps.setString(1, user.getName());
            ps.setInt(2, user.getAge());
            ps.setInt(3, user.getId());
            ps.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    // 根据ID查询用户信息
    public User getUserById(int id) {
        User user = null;
        try {
            PreparedStatement ps = conn.prepareStatement("select * from user where id = ?");
            ps.setInt(1, id);
            ResultSet rs = ps.executeQuery();
            if (rs.next()) {
                user = new User();
                user.setId(rs.getInt("id"));
                user.setName(rs.getString("name"));
                user.setAge(rs.getInt("age"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return user;
    }

    // 查询所有用户信息
    public List<User> getAllUsers() {
        List<User> userList = new ArrayList<User>();
        try {
            PreparedStatement ps = conn.prepareStatement("select * from user");
            ResultSet rs = ps.executeQuery();
            while (rs.next()) {
                User user = new User();
                user.setId(rs.getInt("id"));
                user.setName(rs.getString("name"));
                user.setAge(rs.getInt("age"));
                userList.add(user);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return userList;
    }
}

最后，可以创建一个 `UserServlet` 类作为控制器，处理 HTTP 请求并调用 `UserDao` 对象进行数据操作：

public class UserServlet extends HttpServlet {
    private UserDao userDao = new UserDaoImpl();  // 创建UserDao对象
    
    // 处理GET请求，查询所有用户信息
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        List<User> userList = userDao.getAllUsers();
        request.setAttribute("userList", userList);
        request.getRequestDispatcher("/userList.jsp").forward(request, response);
    }

    // 处理POST请求，添加或修改用户信息
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String action = request.getParameter("action");
        if ("add".equals(action)) {  // 添加用户信息
            String name = request.getParameter("name");
            int age = Integer.parseInt(request.getParameter("age"));
            User user = new User();
            user.setName(name);
            user.setAge(age);
            userDao.addUser(user);
            response.sendRedirect(request.getContextPath() + "/user");
        } else if ("update".equals(action)) {  // 修改用户信息
            int id = Integer.parseInt(request.getParameter("id"));
            String name = request.getParameter("name");
            int age = Integer.parseInt(request.getParameter("age"));
            User user = new User();
            user.setId(id);
            user.setName(name);
            user.setAge(age);
            userDao.updateUser(user);
            response.sendRedirect(request.getContextPath() + "/user");
        }
    }

    // 处理DELETE请求，删除用户信息
    protected void doDelete(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        int id = Integer.parseInt(request.getParameter("id"));
        userDao.deleteUser(id);
        response.getWriter().write("success");
    }
}

最后，可以创建一个 `userList.jsp` 页面显示所有用户信息，并提供添加、修改和删除功能：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>User List</title>
</head>
<body>
    <h1>User List</h1>
    
    <table border="1">
        <tr>
            <th>ID</th>
            <th>Name</th>
            <th>Age</th>
            <th>Edit</th>
            <th>Delete</th>
        </tr>
        <c:forEach items="${userList}" var="user">
            <tr>
                <td>${user.id}</td>
                <td>${user.name}</td>
                <td>${user.age}</td>
                <td><a href="<c:url value='/user/edit'/>?id=${user.id}">Edit</a></td>
                <td><a href="javascript:void(0)" onclick="deleteUser(${user.id}, this)">Delete</a></td>
            </tr>
        </c:forEach>
    </table>
    
    <h2>Add User</h2>
    <form action="<c:url value='/user'/>" method="post">
        <input type="hidden" name="action" value="add"/>
        Name: <input type="text" name="name"/><br/>
        Age: <input type="text" name="age"/><br/>
        <input type="submit" value="Submit"/>
    </form>
    
    <h2>Edit User</h2>
    <form action="<c:url value='/user'/>" method="post">
        <input type="hidden" name="action" value="update"/>
        <input type="hidden" name="id" value="${param.id}"/>
        Name: <input type="text" name="name" value="${user.name}"/><br/>
        Age: <input type="text" name="age" value="${user.age}"/><br/>
        <input type="submit" value="Submit"/>
    </form>
    
    <script>
        // 删除用户信息
        function deleteUser(id, link) {
            if (confirm("Are you sure to delete this user?")) {
                var xhr = new XMLHttpRequest();
                xhr.open("DELETE", "<c:url value='/user'/>?id=" + id, true);
                xhr.onreadystatechange = function() {
                    if (xhr.readyState == 4 && xhr.status == 200) {
                        alert("Delete user successfully.");
                        link.parentNode.parentNode.remove();
                    }
                };
                xhr.send();
            }
        }
    </script>
</body>
</html>

以上就是一个简单的 JavaEE 实现增删改查的示例，可以根据实际需求进行修改和完善。