快学快用系列：一文学会java后端WebApi开发

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>com.mysql</groupId>
        <artifactId>mysql-connector-j</artifactId>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <optional>true</optional>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-validation</artifactId>
    </dependency>
</dependencies>

com.example.demo
├── DemoApplication.java          // 启动类
├── controller/                   // REST 接口层
├── service/                      // 业务逻辑层
├── repository/                   // 数据访问层
├── entity/                       // 实体类（数据库表映射）
├── dto/                          // 请求/响应 DTO（推荐）
├── exception/                    // 全局异常处理
└── config/                       // 配置类

package com.example.demo.entity;

import jakarta.persistence.*;
import lombok.Data;
import java.time.LocalDateTime;

@Entity
@Table(name = "users")
@Data  // Lombok：自动生成 getter/setter/toString 等
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, unique = true)
    private String username;

    @Column(nullable = false)
    private String email;

    private String password;  // 实际项目需加密

    private LocalDateTime createTime = LocalDateTime.now();
}

package com.example.demo.repository;

import com.example.demo.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import java.util.Optional;

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    Optional<User> findByUsername(String username);
    boolean existsByEmail(String email);
}

package com.example.demo.service;

import com.example.demo.entity.User;
import com.example.demo.repository.UserRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import java.util.List;

@Service
public class UserService {

    @Autowired
    private UserRepository userRepository;

    public List<User> getAllUsers() {
        return userRepository.findAll();
    }

    public User getUserById(Long id) {
        return userRepository.findById(id).orElseThrow(() -> new RuntimeException("User not found"));
    }

    @Transactional
    public User createUser(User user) {
        if (userRepository.existsByEmail(user.getEmail())) {
            throw new RuntimeException("Email already exists");
        }
        return userRepository.save(user);
    }

    @Transactional
    public User updateUser(Long id, User updatedUser) {
        User user = getUserById(id);
        user.setUsername(updatedUser.getUsername());
        user.setEmail(updatedUser.getEmail());
        // password 处理...
        return userRepository.save(user);
    }

    @Transactional
    public void deleteUser(Long id) {
        userRepository.deleteById(id);
    }
}

package com.example.demo.controller;

import com.example.demo.entity.User;
import com.example.demo.service.UserService;
import jakarta.validation.Valid;
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;

@RestController
@RequestMapping("/api/v1/users")  // API 版本控制
@CrossOrigin(origins = "*")  // 跨域（生产谨慎配置）
public class UserController {

    @Autowired
    private UserService userService;

    @GetMapping
    public ResponseEntity<List<User>> getAll() {
        return ResponseEntity.ok(userService.getAllUsers());
    }

    @GetMapping("/{id}")
    public ResponseEntity<User> getById(@PathVariable Long id) {
        return ResponseEntity.ok(userService.getUserById(id));
    }

    @PostMapping
    public ResponseEntity<User> create(@Valid @RequestBody User user) {
        return new ResponseEntity<>(userService.createUser(user), HttpStatus.CREATED);
    }

    @PutMapping("/{id}")
    public ResponseEntity<User> update(@PathVariable Long id, @Valid @RequestBody User user) {
        return ResponseEntity.ok(userService.updateUser(id, user));
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> delete(@PathVariable Long id) {
        userService.deleteUser(id);
        return ResponseEntity.noContent().build();
    }
}

package com.example.demo.exception;

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.RestControllerAdvice;

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(RuntimeException.class)
    public ResponseEntity<String> handleRuntimeException(RuntimeException ex) {
        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(ex.getMessage());
    }
}

server:
  port: 8080

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/demo_db?useSSL=false&serverTimezone=Asia/Shanghai
    username: root
    password: yourpassword
  jpa:
    hibernate:
      ddl-auto: update  # 开发用，生产用 none 或 validate
    show-sql: true