深入理解RESTful API的无状态性与数据持久化实践

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity // 声明这是一个JPA实体
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    private String email;

    // 构造函数、Getter和Setter
    public User() {
    }

    public User(String username, String email) {
        this.username = username;
        this.email = email;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import java.util.Optional;

@Repository // 声明这是一个Spring Data JPA仓库
public interface UserRepository extends JpaRepository<User, Long> {
    Optional<User> findByUsername(String username);
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

import java.util.List;
import java.util.Optional;

@RestController // 声明这是一个REST控制器
@RequestMapping("/api/users") // 所有请求都映射到/api/users路径下
public class UserController {

    private final UserRepository userRepository;

    @Autowired // 自动注入UserRepository
    public UserController(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    // 创建新用户 (POST /api/users)
    @PostMapping
    public ResponseEntity<User> createUser(@RequestBody User user) {
        User savedUser = userRepository.save(user); // 将用户保存到数据库
        return new ResponseEntity<>(savedUser, HttpStatus.CREATED);
    }

    // 获取所有用户 (GET /api/users)
    @GetMapping
    public List<User> getAllUsers() {
        return userRepository.findAll(); // 从数据库获取所有用户
    }

    // 获取特定用户 (GET /api/users/{id})
    @GetMapping("/{id}")
    public ResponseEntity<User> getUserById(@PathVariable Long id) {
        Optional<User> user = userRepository.findById(id); // 从数据库获取用户
        return user.map(value -> new ResponseEntity<>(value, HttpStatus.OK))
                   .orElseGet(() -> new ResponseEntity<>(HttpStatus.NOT_FOUND));
    }

    // 更新用户 (PUT /api/users/{id})
    @PutMapping("/{id}")
    public ResponseEntity<User> updateUser(@PathVariable Long id, @RequestBody User userDetails) {
        return userRepository.findById(id)
                .map(user -> {
                    user.setUsername(userDetails.getUsername());
                    user.setEmail(userDetails.getEmail());
                    User updatedUser = userRepository.save(user); // 更新数据库中的用户
                    return new ResponseEntity<>(updatedUser, HttpStatus.OK);
                })
                .orElseGet(() -> new ResponseEntity<>(HttpStatus.NOT_FOUND));
    }

    // 删除用户 (DELETE /api/users/{id})
    @DeleteMapping("/{id}")
    public ResponseEntity<HttpStatus> deleteUser(@PathVariable Long id) {
        try {
            userRepository.deleteById(id); // 从数据库删除用户
            return new ResponseEntity<>(HttpStatus.NO_CONTENT);
        } catch (Exception e) {
            return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
        }
    }
}