Spring Boot 核心特性之组件自动装配

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(DelegatingWebMvcConfiguration.class)
public @interface EnableWebMvc {}

@Configuration
public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {}

 @Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {}

public class EnableAutoConfigurationImportSelector
  extends AutoConfigurationImportSelector {}
public class AutoConfigurationImportSelector
		implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,
BeanFactoryAware, EnvironmentAware, Ordered {
  @Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {}
}

@Configuration
@Profile("development")
public class StandaloneDataConfig {
    @Bean
    public DataSource dataSource() {}
}
@Configuration
@Profile("production")
public class JndiDataConfig {
    @Bean
    public DataSource dataSource() throws Exception {}
}

@Configuration
public class SomeConfig {
    @Bean("dataSource")
    @Profile("development")
    public DataSource standaloneDataSource() {}
    @Bean("dataSource")
    @Profile("production")
    public DataSource jndiDataSource() throws Exception {}
}

AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.getEnvironment().setActiveProfiles("development");
ctx.register(SomeConfig.class, StandaloneDataConfig.class, JndiDataConfig.class);
ctx.refresh();

@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Conditional(OnClassCondition.class)
public @interface ConditionalOnClass {}

激活：@EnableAutoConfiguration
Spring Boot 默认没有激活自动装配，存在@SpringBootApplication注解中

参考:org.springframework.boot.autoconfigure.AutoConfigurationImport

Selector#getCandidateConfigurations
 
 

配置：/META-INF/spring.factories

 规约文件，META-INFO指的是元信息目录，如spring.handlers、spring.schemas等

参考:org.springframework.core.io.support.SpringFactoriesLoader
 

实现：XxxAutoConfiguration
ex: org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration
 

@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		try {
          	//加载spring-boot-autoconfigure-1.5.6.RELEASE.jar!\META-INF\spring-autoconfigure-metadata.properties
			AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
					.loadMetadata(this.beanClassLoader);
          	 //获取EnableAutoConfiguration里的exclude和excludeName-->LinkedHashMap-->AnnotationAttributes
			AnnotationAttributes attributes = getAttributes(annotationMetadata);
             //获取依赖里所有的xx.jar!\META-INF\spring.factories的value
			List<String> configurations = getCandidateConfigurations(annotationMetadata,
					attributes);
             //利用Set去重
			configurations = removeDuplicates(configurations);
             //排序->先按照字母排序->再按照Order排序(ex:MessageSourceAutoConfiguration#@AutoConfigureOrder)->然后根据@AutoConfigureBefore @AutoConfigureAfter(ex:WebSocketAutoConfiguration#@AutoConfigureBefore)排序
			configurations = sort(configurations, autoConfigurationMetadata);
             //对attributes封装与去重得到exclusions
			Set<String> exclusions = getExclusions(annotationMetadata, attributes);
			checkExcludedClasses(configurations, exclusions);
             //去掉exclusions里的XxAutoConf...
			configurations.removeAll(exclusions);
             //加载过滤器，对不满足ex:默认有一个OnClassCondition(org.springframework.boot.autoconfigure.AutoConfigurationImportSelector#getAutoConfigurationImportFilters()，见下图)的会排除掉()
			configurations = filter(configurations, autoConfigurationMetadata);
			fireAutoConfigurationImportEvents(configurations, exclusions);
			return configurations.toArray(new String[configurations.size()]);
		}
		catch (IOException ex) {
			throw new IllegalStateException(ex);
		}
	}

org.springframework.context.support.PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors
org.springframework.context.annotation.ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry
org.springframework.context.annotation.ConfigurationClassPostProcessor#processConfigBeanDefinitions
org.springframework.context.annotation.ConfigurationClassParser#parse(java.util.Set<org.springframework.beans.factory.config.BeanDefinitionHolder>)
org.springframework.context.annotation.ConfigurationClassParser#processDeferredImportSelectors
String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());
processImports(configClass, asSourceClass(configClass), asSourceClasses(imports), false);