详解Spring Boot最核心的27个注解，你了解多少？

@Configuration
public class TaskAutoConfiguration {

  @Bean
  @Profile("biz-electrfence-controller")
  public BizElectrfenceControllerJob bizElectrfenceControllerJob() {
    return new BizElectrfenceControllerJob();
  }

  @Bean
  @Profile("biz-consume-1-datasync")
  public BizBikeElectrFenceTradeSyncJob bizBikeElectrFenceTradeSyncJob() {
    return new BizBikeElectrFenceTradeSyncJob();
  }
}

@ComponentScan(value = "com.abacus.check.api")
public class CheckApiApplication {
  public static void main(String[] args) {
    SpringApplication.run(CheckApiApplication.class, args);
  }
}

@SpringBootApplication(scanBasePackages = {"com.abacus.check.api", "com.abacus.check.service"})
public class CheckApiApplication {
  public static void main(String[] args) {
    SpringApplication.run(CheckApiApplication.class, args);
  }
}

//类定义
public class Square {}

public class Circular {}

//导入
@Import({Square.class,Circular.class})
@Configuration
public class MainConfig{}

 @ImportResource("classpath:spring-redis.xml")   //导入xml配置

public class CheckApiApplication {
  public static void main(String[] args) {
    SpringApplication.run(CheckApiApplication.class, args);
  }
}

@SpringBootApplication(exclude = {
    MongoAutoConfiguration.class,
    MongoDataAutoConfiguration.class,
    DataSourceAutoConfiguration.class,
    ValidationAutoConfiguration.class,
    MybatisAutoConfiguration.class,
    MailSenderAutoConfiguration.class,
})
public class API {
  public static void main(String[] args) {
    SpringApplication.run(API.class, args);
  }
}

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage//导入AutoConfigurationImportSelector的子类@Import({EnableAutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
  String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

  Class<?>[] exclude() default {};

  String[] excludeName() default {};
}

@Bean
//当前环境上下文存在DefaultMQProducer实例时，才能创建RocketMQProducerLifecycle这个Bean
@ConditionalOnBean(DefaultMQProducer.class)
public RocketMQProducerLifecycle rocketMQLifecycle() {
   return new RocketMQProducerLifecycle();
}

 @Bean
 //仅当当前环境上下文缺失RocketMQProducer对象时，才允许创建RocketMQProducer Bean对象
 @ConditionalOnMissingBean(RocketMQProducer.class)
 public RocketMQProducer mqProducer() {
   return new RocketMQProducer();
 }

 @Bean
 //当classpath中存在类HealthIndicator时，才创建HealthIndicator Bean对象
 @ConditionalOnClass(HealthIndicator.class)
 public HealthIndicator rocketMQProducerHealthIndicator(Map<String, DefaultMQProducer> producers) {
   if (producers.size() == 1) {
     return new RocketMQProducerHealthIndicator(producers.values().iterator().next());
   }
 }

 @Bean
 //匹配属性rocketmq.producer.enabled值是否为true
 @ConditionalOnProperty(value = "rocketmq.producer.enabled", havingValue = "true", matchIfMissing = true)
 public RocketMQProducer mqProducer() {
   return new RocketMQProducer();
 }

@Configuration
@ConditionalOnExpression("${enabled:false}")
public class BigpipeConfiguration {
  @Bean
  public OrderMessageMonitor orderMessageMonitor(ConfigContext configContext) {
    return new OrderMessageMonitor(configContext);
  }
}

@Bean
@ConditionalOnResource(resources="classpath:shiro.ini")
protected Realm iniClasspathRealm(){
 return new Realm();
}

@Data
@ConfigurationProperties("rocketmq.consumer")
public class RocketMQConsumerProperties extends RocketMQProperties {
  private boolean enabled = true;

  private String consumerGroup;

  private MessageModel messageModel = MessageModel.CLUSTERING;

  private ConsumeFromWhere consumeFromWhere = ConsumeFromWhere.CONSUME_FROM_LAST_OFFSET;

  private int consumeThreadMin = 20;

  private int consumeThreadMax = 64;

  private int consumeConcurrentlyMaxSpan = 2000;

  private int pullThresholdForQueue = 1000;

  private int pullInterval = 0;

  private int consumeMessageBatchMaxSize = 1;

  private int pullBatchSize = 32;
}

@Configuration
@EnableConfigurationProperties({
  RocketMQProducerProperties.class,
  RocketMQConsumerProperties.class,
})
@AutoConfigureOrder
public class RocketMQAutoConfiguration {
  @Value("${spring.application.name}")
  private String applicationName;
}

@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration {
}

 @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE) // 自动配置里面的最高优先级
 @Configuration
 @ConditionalOnWebApplication // 仅限于web应用
 @Import(BeanPostProcessorsRegistrar.class) // 导入内置容器的设置
 public class EmbeddedServletContainerAutoConfiguration {
   @Configuration
   @ConditionalOnClass({ Servlet.class, Tomcat.class })
   @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
   public static class EmbeddedTomcat {
     // ...
   }

   @Configuration
   @ConditionalOnClass({ Servlet.class, Server.class, Loader.class, WebAppContext.class })
   @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
   public static class EmbeddedJetty {
     // ...
   }
}