Feign踩坑源码分析--@FeignClient注入容器

一. @EnableFeignClients

　　1.1.类介绍

　　从上面注释可以看出是扫描声明了@FeignClient接口的类，还引入了 FeignClientsRegistrar类，从字面意思可以看出是进行了 FeignClient 客户端类的注册。

　　1.2.FeignClientsRegistrar 详解

　　最主要的一个方法：registerBeanDefinitions注册bean定义信息，主要功能是实现向容器注册Feign客户端配置信息和所有的使用了@FeignClient的类；

　　1.2.1.registerDefaultConfiguration()

private void registerDefaultConfiguration(AnnotationMetadata metadata,
        BeanDefinitionRegistry registry) {
    // 获取@EnableFeignClients注解的属性和值
    Map<String, Object> defaultAttrs = metadata
            .getAnnotationAttributes(EnableFeignClients.class.getName(), true);
    // 获取属性中的默认配置 defaultConfiguration，name是main主程序
    if (defaultAttrs != null && defaultAttrs.containsKey("defaultConfiguration")) {
        String name;
        if (metadata.hasEnclosingClass()) {
            name = "default." + metadata.getEnclosingClassName();
        }
        else {
            name = "default." + metadata.getClassName();
        }
        //默认配置信息进行容器注册
        registerClientConfiguration(registry, name,
                defaultAttrs.get("defaultConfiguration"));
    }
}

　　1.2.1.1.registerClientConfiguration

private void registerClientConfiguration(BeanDefinitionRegistry registry, Object name,
        Object configuration) {
    // 创建一个 FeignClientSpecification.class 构造器
    BeanDefinitionBuilder builder = BeanDefinitionBuilder
            .genericBeanDefinition(FeignClientSpecification.class);
    builder.addConstructorArgValue(name);
    builder.addConstructorArgValue(configuration);
    // 向容器中注册默认配置
    registry.registerBeanDefinition(
            name + "." + FeignClientSpecification.class.getSimpleName(),
            builder.getBeanDefinition());
}

　　1.2.1.2.registerBeanDefinition

　　核心代码在：org.springframework.beans.factory.support.DefaultListableBeanFactory#registerBeanDefinition

    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

            ............
            if (hasBeanCreationStarted()) {
                // Cannot modify startup-time collection elements anymore (for stable iteration)
                synchronized (this.beanDefinitionMap) {
                    //放到beanDefinitionMap，到AbstractApplicationContext#finishBeanFactoryInitialization(beanFactory)中取出进行bean实例化
                    //此时是处于invokeBeanFactoryPostProcessors(beanFactory);阶段，进行BeanDefinitionRegistryPostProcessor的处理
                    this.beanDefinitionMap.put(beanName, beanDefinition);
                    List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    removeManualSingletonName(beanName);
                }
            }
            ..........
    }

　　1.2.2.registerFeignClients()

    public void registerFeignClients(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        //获取一个扫描器
        ClassPathScanningCandidateComponentProvider scanner = getScanner();
        //设置资源路径
        scanner.setResourceLoader(this.resourceLoader);
        //包路径
        Set<String> basePackages;
        //获取EnableFeignClients注解的参数和值，有5个值，其中clients对应的class[0]是没有值的
        Map<String, Object> attrs = metadata
                .getAnnotationAttributes(EnableFeignClients.class.getName());
        //定义一个 FeignClient 注解类型过滤器
        AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
                FeignClient.class);
        //clients为class[0]，长度为0
        final Class<?>[] clients = attrs == null ? null
                : (Class<?>[]) attrs.get("clients");
        if (clients == null || clients.length == 0) {
            //FeignClient 注解过滤器添加到扫描器中
            scanner.addIncludeFilter(annotationTypeFilter);
            //获取Application对应的根路径包
            basePackages = getBasePackages(metadata);
        }
        //clients不为空：FeignClient 注解过滤器添加到扫描器中、获取包路径
        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)));
        }
        //遍历包路径，获取标记@FeignClient注解的接口向容器中注入
        for (String basePackage : basePackages) {
            Set<BeanDefinition> candidateComponents = scanner
                    .findCandidateComponents(basePackage);
            for (BeanDefinition candidateComponent : candidateComponents) {
                if (candidateComponent instanceof AnnotatedBeanDefinition) {
                    // verify annotated class is an interface
                    AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
                    AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
                    Assert.isTrue(annotationMetadata.isInterface(),
                            "@FeignClient can only be specified on an interface");
                    //获取@FeignClient的参数和值
                    Map<String, Object> attributes = annotationMetadata
                            .getAnnotationAttributes(
                                    FeignClient.class.getCanonicalName());

                    String name = getClientName(attributes);
                    //再次更新配置
                    registerClientConfiguration(registry, name,
                            attributes.get("configuration"));
                    //注册
                    registerFeignClient(registry, annotationMetadata, attributes);
                }
            }
        }
    }

　　1.2.2.2.registerFeignClient

    //定义一个 FeignClientFactoryBean bean定义构造器(重点）
    BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);
    ..........
    //前面根据attributes进行属性赋值后注入到Spring容器中
    BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);

二.@FeignClient

　　从上面可以看到在注册客户端时注册了一个FeignClientFactoryBean（对于FactoryBean的扩展知识和案例），所以FeignClient的获取是从getObject()获取的：

　　2.1.getTarget()

	<T> T getTarget() {
		//获取创建feign实例的工厂
		FeignContext context = this.applicationContext.getBean(FeignContext.class);
		//获取feign构造器
		Feign.Builder builder = feign(context);
		//url拼接
		if (!StringUtils.hasText(this.url)) {
			//拼接name
			if (!this.name.startsWith("http")) {
				this.url = "http://" + this.name;
			}
			else {
				this.url = this.name;
			}
			//拼接path
			this.url += cleanPath();
			//创建实例
			return (T) loadBalance(builder, context,
					new HardCodedTarget<>(this.type, this.name, this.url));
		}
		if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
			this.url = "http://" + this.url;
		}
		String url = this.url + cleanPath();
		Client client = getOptional(context, Client.class);
		if (client != null) {
			if (client instanceof LoadBalancerFeignClient) {
				// not load balancing because we have a url,
				// but ribbon is on the classpath, so unwrap
				client = ((LoadBalancerFeignClient) client).getDelegate();
			}
			builder.client(client);
		}
		Targeter targeter = get(context, Targeter.class);
		return (T) targeter.target(this, builder, context,
				new HardCodedTarget<>(this.type, this.name, url));
	}

　　2.1.1. feign()

    //添加日志对象、编码器、解码器、解析规则器
    protected Feign.Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(this.type);

        // @formatter:off
        Feign.Builder builder = get(context, Feign.Builder.class)
                // required values
                .logger(logger)
                .encoder(get(context, Encoder.class))
                .decoder(get(context, Decoder.class))
                //SpringMvcContract:对RequestMapping、RequestParam、RequestHeader等注解进行解析
                .contract(get(context, Contract.class));
        // @formatter:on

        configureFeign(context, builder);

        return builder;
    }

　　2.1.2. loadBalance()

    protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
            HardCodedTarget<T> target) {
        //根据context上下文获取客户端实例，client:TraceLoadBalancerFeignClient,负载均衡
        Client client = getOptional(context, Client.class);
        if (client != null) {
            //客户端创建
            builder.client(client);
            //获取HystrixTargerer
            Targeter targeter = get(context, Targeter.class);
            //调用HystrixTargeter#target进行实例创建
            return targeter.target(this, builder, context, target);
        }

        throw new IllegalStateException(
                "No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");
    }

　2.1.3. HystrixTargeter#target

class HystrixTargeter implements Targeter {

@Override
public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
        FeignContext context, Target.HardCodedTarget<T> target) {
    // 不是同一种类型，进入feign#target方法
    if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
        return feign.target(target);
    }
    ......
}

　2.1.4. Feign.Builder#target

    public <T> T target(Target<T> target) {
      return build().newInstance(target);
    }

　2.1.4.1. Feign.Builder#target

    public Feign build() {
      //同步方法处理工厂，构建了日志级别信息
      SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
          new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
              logLevel, decode404, closeAfterDecode, propagationPolicy);
      //解析信息：编码、解密、同步方法处理工厂
      ParseHandlersByName handlersByName =
          new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder,
              errorDecoder, synchronousMethodHandlerFactory);
      //new对象
      return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);
    }

　2.1.4.2.ReflectiveFeign#newInstance

  @Override
  public <T> T newInstance(Target<T> target) {
    //得到feign类的定义方法
    Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
    //定义方法存放集合
    Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
    //默认方法存放集合
    List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();
    //对feign类方法进行遍历
    for (Method method : target.type().getMethods()) {
      if (method.getDeclaringClass() == Object.class) {
        continue;
        //默认方法
      } else if (Util.isDefault(method)) {
        DefaultMethodHandler handler = new DefaultMethodHandler(method);
        defaultMethodHandlers.add(handler);
        methodToHandler.put(method, handler);
      } else {
        methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
      }
    }
    //jdk动态代理创建对象
    InvocationHandler handler = factory.create(target, methodToHandler);
    T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
        new Class<?>[] {target.type()}, handler);

    for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
      defaultMethodHandler.bindTo(proxy);
    }
    return proxy;
  }

三.总结

　　主要应用了FactoryBean的特性getObject()进行jdk动态创建一个ReflectiveFeign的代理对象。