Springboot自動(dòng)裝配

springboot啟動(dòng)時(shí)我們常見的就是一個(gè)注解@SpringBootApplication 和 SpringApplication的run方法笨鸡，前面介紹過run（http://www.reibang.com/p/90ebeec86f64）,今天詳細(xì)看一下@SpringBootApplication匀借。

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class);
    }
}

@SpringBootApplication是一個(gè)注解的組合恤磷，進(jìn)去看下它里面

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
      @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
      @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {

主要包含@SpringBootConfiguration狮鸭，@EnableAutoConfiguration浆竭，@ComponentScan

首先@ComponentScan,默認(rèn)掃描的是與該類同級(jí)的類或者同級(jí)包下的所有類

其次@SpringBootConfiguration性昭，只是封裝了@Configuration，把啟動(dòng)類指定為一個(gè)javaConfig（會(huì)在容器刷新中的invokeBeanFactoryPostProcessors里進(jìn)行解析執(zhí)行）

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {

}

最后@EnableAutoConfiguration

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

   String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

   /**
    * Exclude specific auto-configuration classes such that they will never be applied.
    * @return the classes to exclude
    */
   Class<?>[] exclude() default {};

   /**
    * Exclude specific auto-configuration class names such that they will never be
    * applied.
    * @return the class names to exclude
    * @since 1.3.0
    */
   String[] excludeName() default {};

}

@EnableAutoConfiguration里面有兩個(gè)主要的注解@AutoConfigurationPackage和@Import(AutoConfigurationImportSelector.class)捎琐。

@AutoConfigurationPackage蓄髓，該注解的作用是添加該注解的類所在的package（啟動(dòng)類所在路徑） 作為 自動(dòng)配置package 進(jìn)行管理叉庐。

@Import(AutoConfigurationImportSelector.class)，看一下后面它注冊到容器中的bean AutoConfigurationImportSelector.class会喝。

public class AutoConfigurationImportSelector
      implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,
      BeanFactoryAware, EnvironmentAware, Ordered {
        //省略陡叠。。肢执。枉阵。。

其中DeferredImportSelector extends ImportSelector预茄，所以會(huì)執(zhí)行到selectImports岭妖，DeferredImportSelector 和 ImportSelector的區(qū)別在于DeferredImportSelector為延時(shí)加載，等configure都加載完了才開始加載

看一下AutoConfigurationImportSelector里的selectImports

@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
  //判斷是否需要自動(dòng)裝配
   if (!isEnabled(annotationMetadata)) {
      return NO_IMPORTS;
   }
  //從META-INF/spring-autoconfigure-metadata.properties讀取元數(shù)據(jù)與元數(shù)據(jù)的相關(guān)屬性
   AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
         .loadMetadata(this.beanClassLoader);
   AnnotationAttributes attributes = getAttributes(annotationMetadata);
  //讀取META-INF/spring.factories下的EnableAutoConfiguration的配置(這里用到了SpringFactoriesLoader反璃，和啟動(dòng)過程中加載spring.factories中的初始化器和監(jiān)聽器是同一個(gè))
   List<String> configurations = getCandidateConfigurations(annotationMetadata,
         attributes);
  //排除與過濾
   configurations = removeDuplicates(configurations);
   Set<String> exclusions = getExclusions(annotationMetadata, attributes);
   checkExcludedClasses(configurations, exclusions);
   configurations.removeAll(exclusions);
   configurations = filter(configurations, autoConfigurationMetadata);
  //讓所有配置在META-INF/spring.factories下的AutoConfigurationImportListener執(zhí)行AutoConfigurationImportEvent事件
   fireAutoConfigurationImportEvents(configurations, exclusions);
   return StringUtils.toStringArray(configurations);
}

上面這些過程只是確定了需要自定裝配的類昵慌，真正開始處理是在容器刷新中的invokeBeanFactoryPostProcessors方法里，里面用了ConfigurationClassPostProcessor這個(gè)后置處理來處理并且用相應(yīng)的解析器來解析@Configuration注解修飾的類(@Component淮蜈、@ComponentScan斋攀、@Import、@ImportResource修飾的類也會(huì)被處理)梧田，具體可參考http://www.reibang.com/p/ab0b7df24c01

另外淳蔼，每個(gè)需要自動(dòng)裝配的類都可以根據(jù)條件判斷是否進(jìn)行裝配@ConditionalXXX，舉例mq

@Configuration
@ConditionalOnClass({ RabbitTemplate.class, Channel.class })
@EnableConfigurationProperties(RabbitProperties.class)
@Import(RabbitAnnotationDrivenConfiguration.class)
public class RabbitAutoConfiguration {