@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients(basePackages = {"com.aiqinhai.client2.feignclient"})
public class Client2Application {
    public static void main(String[] args) {
        SpringApplication.run(Client2Application.class, args);
    }
}

/**
 * 掃描注解@FeignClient標(biāo)注的接口
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {
 //同basePackages
 String[] value() default {};
        //掃描的package.
 String[] basePackages() default {};
 //feigin client全局配置，默認(rèn)配置在FeignClientsConfiguration類中
 Class<?>[] defaultConfiguration() default {};
 //@FeignClient注解的接口，如果指定了該屬性，則關(guān)閉掃描。
 Class<?>[] clients() default {};
}

class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar,
		ResourceLoaderAware, EnvironmentAware {
	//包掃描方法入口
	@Override
	public void registerBeanDefinitions(AnnotationMetadata metadata,
			BeanDefinitionRegistry registry) {
		//注冊(cè)默認(rèn)配置bean到ioc
		registerDefaultConfiguration(metadata, registry);
		//注冊(cè)@FeignClients標(biāo)注的接口bean,為其生成動(dòng)態(tài)代理
		registerFeignClients(metadata, registry);
	}
	private void registerDefaultConfiguration(AnnotationMetadata metadata,
			BeanDefinitionRegistry registry) {
		//獲取@EnableFeignClients注解屬性
		Map<String, Object> defaultAttrs = metadata
				.getAnnotationAttributes(EnableFeignClients.class.getName(), true);
		if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {
			String name;
			if (metadata.hasEnclosingClass()) {
				name = "default." + metadata.getEnclosingClassName();
			}
			else {
				name = "default." + metadata.getClassName();
			}
			//注冊(cè)@EnableFeignClients defaultConfiguration 類中定義的bean到ioc
			registerClientConfiguration(registry, name,
					defaultAttrs.get("defaultConfiguration"));		}
	}
	public void registerFeignClients(AnnotationMetadata metadata,
			BeanDefinitionRegistry registry) {
		//spring 掃描工具類
		ClassPathScanningCandidateComponentProvider scanner = getScanner();
		scanner.setResourceLoader(this.resourceLoader);
        //待掃描的包
		Set<String> basePackages;
        //@EnableFeignClients注解屬性
		Map<String, Object> attrs = metadata
				.getAnnotationAttributes(EnableFeignClients.class.getName());
		//@FeignClient注解過濾器，只掃描@FeignClient注解標(biāo)注的接口
		AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
				FeignClient.class);
		//解析@EnableFeignClient 屬性clients
		final Class<?>[] clients = attrs == null ? null
				: (Class<?>[]) attrs.get("clients");
		//如果@EnableFeignClient沒有指定clients,則開啟包掃描，否則關(guān)閉掃描，使用clients
		if (clients == null || clients.length == 0) {
			scanner.addIncludeFilter(annotationTypeFilter);
			basePackages = getBasePackages(metadata);
		}
		else {
			final Set<String> clientClasses = new HashSet<>();
			basePackages = new HashSet<>();
			for (Class<?> clazz : clients) {
				basePackages.add(ClassUtils.getPackageName(clazz));
				clientClasses.add(clazz.getCanonicalName());
			}
			AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {
				@Override
				protected boolean match(ClassMetadata metadata) {
					String cleaned = metadata.getClassName().replaceAll("\\$", ".");
					return clientClasses.contains(cleaned);
				}
			};
			scanner.addIncludeFilter(
					new AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));
		}
		for (String basePackage : basePackages) {
		    //從類路徑下的所有.class文件中掃描@FeignClient注解的接口
			Set<BeanDefinition> candidateComponents = scanner
					.findCandidateComponents(basePackage);
			for (BeanDefinition candidateComponent : candidateComponents) {
				if (candidateComponent instanceof AnnotatedBeanDefinition) {
					// verify annotated class is an interface
					AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
					//獲取注解
					AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
					//@FeignClient注解必須應(yīng)用在接口上，否則拋出異常。
					Assert.isTrue(annotationMetadata.isInterface(),
							"@FeignClient can only be specified on an interface");
                        //獲取FeignClient注解屬性
					Map<String, Object> attributes = annotationMetadata
							.getAnnotationAttributes(
									FeignClient.class.getCanonicalName());
                        //服務(wù)名稱
					String name = getClientName(attributes);
					//注冊(cè)configuration中指定的bean
					registerClientConfiguration(registry, name,
							attributes.get("configuration"));
					//生成FeignClient bean,并注冊(cè)到ioc
					registerFeignClient(registry, annotationMetadata, attributes);
				}
			}
		}
	}
 
    //生成bean,注入到IOC容器
	private void registerFeignClient(BeanDefinitionRegistry registry,
			AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
		// feignclient類名稱
		String className = annotationMetadata.getClassName();
		BeanDefinitionBuilder definition = BeanDefinitionBuilder
				.genericBeanDefinition(FeignClientFactoryBean.class);
		validate(attributes);
		definition.addPropertyValue("url", getUrl(attributes));
		definition.addPropertyValue("path", getPath(attributes));
		String name = getName(attributes);
		definition.addPropertyValue("name", name);
		definition.addPropertyValue("type", className);
		definition.addPropertyValue("decode404", attributes.get("decode404"));
		definition.addPropertyValue("fallback", attributes.get("fallback"));
		definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
		definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE); 
		String alias = name + "FeignClient";
		AbstractBeanDefinition beanDefinition = definition.getBeanDefinition(); 
		boolean primary = (Boolean)attributes.get("primary"); // has a default, won't be null
		beanDefinition.setPrimary(primary);
		String qualifier = getQualifier(attributes);
		if (StringUtils.hasText(qualifier)) {
			alias = qualifier;
		}
		BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
				new String[] { alias });
		//注冊(cè)到ioc
		BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
	}
}