SpringBoot 常用注解详细解析

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;
// 方式一：直接在 @SpringBootApplication 上指定扫描包
@SpringBootApplication(scanBasePackages = {
        "com.example.service",
        "com.example.web"
})
public class CustomScanApplication {
    public static void main(String[] args) {
        SpringApplication.run(CustomScanApplication.class, args);
    }
}
// 方式二：配合 @ComponentScan 单独配置（等价写法）
@SpringBootApplication
@ComponentScan(basePackages = {
        "com.example.service",
        "com.example.web"
})
class AnotherApplication {
}

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class DemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

import org.springframework.stereotype.Service;
import org.springframework.stereotype.Repository;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Service
public class UserService {
    public String getUserName() {
        return "Tom";
    }
}
@Repository
public class UserRepository {
    // 模拟持久层
}
@Configuration
public class AppConfig {
    @Bean
    public String commonBean() {
        return "I am a bean";
    }
}

@Configuration
public class BeanConfig {
    @Bean
    public User user() {
        return new User();
    }
    @Bean
    public List<User> userList() {
        // 虽然看起来调用了两次 user()，但因为有 CGLIB 代理，这里返回的是同一个单例 Bean
        return Arrays.asList(user(), user());
    }
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;
public interface MessageService {
    String send();
}
@Component("emailService")
@Primary // 同类型多个 Bean 时，优先注入
class EmailService implements MessageService {
    @Override
    public String send() {
        return "send email";
    }
}
@Component("smsService")
class SmsService implements MessageService {
    @Override
    public String send() {
        return "send sms";
    }
}
@Component
class MessageController {
    // 指定注入 smsService，而不是默认的 @Primary emailService
    @Autowired
    @Qualifier("smsService")
    private MessageService messageService;
}

// application.yml
app:
  name: demo-app
  version: v1.0
server:
  port: 8081

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;
@Component
@ConfigurationProperties(prefix = "app")
public class AppProperties {
    private String name;
    private String version;
    // getter / setter 省略
}
@Component
public class ConfigDemo {
    // 读取单个配置
    @Value("${server.port}")
    private int serverPort;
}

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@RequestMapping("/users")
public class UserController {
    @GetMapping("/{id}")
    public String getUser(@PathVariable Long id) {
        return "user id = " + id;
    }
    @PostMapping
    public User createUser(@RequestBody User user) {
        // 简化处理：直接返回请求体
        return user;
    }
}

import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
@RestController
@CrossOrigin(origins = "http://localhost:3000")
public class DemoController {
    // GET /hello?name=Tom
    @GetMapping("/hello")
    public String hello(@RequestParam String name) {
        return "hello " + name;
    }
    // GET /order/100
    @GetMapping("/order/{id}")
    public String getOrder(@PathVariable("id") Long orderId) {
        return "order id = " + orderId;
    }
}

// application.yml
feature:
  sms:
    enabled: true

import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.stereotype.Component;
@Component
@ConditionalOnProperty(prefix = "feature.sms", name = "enabled", havingValue = "true")
public class SmsSender {
    // 只有当 feature.sms.enabled = true 时才会装配
}

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
@SpringBootApplication
@EnableScheduling
public class ScheduleApplication {
    public static void main(String[] args) {
        SpringApplication.run(ScheduleApplication.class, args);
    }
}
@Component
class TaskJob {
    // 每 5 秒执行一次
    @Scheduled(fixedRate = 5000)
    public void run() {
        System.out.println("task running...");
    }
}

import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
@Service
public class OrderService {
    @Transactional(rollbackFor = Exception.class)
    public void createOrder() {
        // 1. 插入订单表
        // 2. 扣减库存
        // 3. 发生异常时整体回滚
    }
}

// 引入依赖（通常在 pom.xml 中）：
// spring-boot-starter-validation
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.Max;
public class UserDTO {
    @NotBlank(message = "用户名不能为空")
    private String name;
    @Max(value = 120, message = "年龄不能超过 120")
    private int age;
    // getter / setter 省略
}

import jakarta.validation.Valid;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class ValidateController {
    @PostMapping("/users")
    public String create(@Valid @RequestBody UserDTO user) {
        return "ok";
    }
}