OpenFeign源码分析

compile ‘org.springframework.cloud:spring-cloud-starter-openfeign‘

@SpringBootApplication
@EnableFeignClients(basePackages = {"com.yue.consumer"}) //开启 Feign支持，扫描指定包下接口
public class WebApplication {

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

　　 //声明 feign接口
    @FeignClient(name = "service-name", path = "/v1", url = "http://sck-demo-provider", primary = false)
    static interface FeignService {
        
        //调用服务接口
        @RequestMapping("/test")
        public String getName();
    }
}

@RestController
@RequestMapping("/test")
public class TestController {

    @Autowired
    FeignService feignService;

    @RequestMapping("/getString")
    public String getStr(){
        return feignService.getName();
    }
}

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(FeignClientsRegistrar.class)
public @interface EnableFeignClients {

    /**
     * basePackages 属性的别名。 允许使用更简洁的注释声明
     */
    String[] value() default {};

    /**
     * 扫描包下带注释的组件
     */
    String[] basePackages() default {};

    /**
     * basePackages() 的类型安全的替代方法，用于指定要扫描带注释的组件的软件包。 指定类别的包装将被扫描。
     */
    Class<?>[] basePackageClasses() default {};

    /**
     * 适用于所有自定义@Configuration,可以包含组成客户端的部分的@Bean 
     */
    Class<?>[] defaultConfiguration() default {};

    /**
     * 用@FeignClient注释的类的列表。 如果不为空，则禁用类路径*扫描。
     */
    Class<?>[] clients() default {};

}

class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
    
    // 获取 name
    static String getName(String name) {
        if (!StringUtils.hasText(name)) {
            return "";
        }

        String host = null;
        try {
            String url;
            if (!name.startsWith("http://") && !name.startsWith("https://")) {
                url = "http://" + name;
            }
            else {
                url = name;
            }
            host = new URI(url).getHost();

        }
        catch (URISyntaxException e) {
        }
        Assert.state(host != null, "Service id not legal hostname (" + name + ")");
        return name;
    }
    //获取 url
    static String getUrl(String url) {
        if (StringUtils.hasText(url) && !(url.startsWith("#{") && url.contains("}"))) {
            if (!url.contains("://")) {
                url = "http://" + url;
            }
            try {
                new URL(url);
            }
            catch (MalformedURLException e) {
                throw new IllegalArgumentException(url + " is malformed", e);
            }
        }
        return url;
    }
    //获取 path
    static String getPath(String path) {
        if (StringUtils.hasText(path)) {
            path = path.trim();
            if (!path.startsWith("/")) {
                path = "/" + path;
            }
            if (path.endsWith("/")) {
                path = path.substring(0, path.length() - 1);
            }
        }
        return path;
    }
    
    
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        //注册configuration
        registerDefaultConfiguration(metadata, registry);
        //注册注解
        registerFeignClients(metadata, registry);
    }

    private void registerDefaultConfiguration(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        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();
            }
            //注册客户端配置
            registerClientConfiguration(registry, name, defaultAttrs.get("defaultConfiguration"));
        }
    }
    
    private void registerClientConfiguration(BeanDefinitionRegistry registry, Object name,
            Object configuration) {
        //加载FeignClientSpecification bean
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(FeignClientSpecification.class);
        builder.addConstructorArgValue(name);
        builder.addConstructorArgValue(configuration);
        //注册
        registry.registerBeanDefinition(name + "." + FeignClientSpecification.class.getSimpleName(),builder.getBeanDefinition());
    }

    public void registerFeignClients(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        ClassPathScanningCandidateComponentProvider scanner = getScanner();
        scanner.setResourceLoader(this.resourceLoader);

        Set<String> basePackages;

        Map<String, Object> attrs = metadata
                .getAnnotationAttributes(EnableFeignClients.class.getName());
        // 扫描带有FeignClient注解的类
        AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(FeignClient.class);
        //获取@EnableFeignClients 中clients的值
        final Class<?>[] clients = attrs == null ? null : (Class<?>[]) attrs.get("clients");
        if (clients == null || clients.length == 0) {
            //如果没有设置，那么设置类型过滤器
            scanner.addIncludeFilter(annotationTypeFilter);
            // 如果没有设置，则扫描的包路径为 @EnableFeignClients 注解所在的包
            basePackages = getBasePackages(metadata);
        }
        else {
            final Set<String> clientClasses = new HashSet<>();
            basePackages = new HashSet<>();
            //设置了则使用注解属性来进行扫描注册
            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)));
        }
        //循环扫描注册
        for (String basePackage : basePackages) {
            Set<BeanDefinition> candidateComponents = scanner
                    .findCandidateComponents(basePackage);
            for (BeanDefinition candidateComponent : candidateComponents) {
                if (candidateComponent instanceof AnnotatedBeanDefinition) {
                    // 验证带注释的类必须是接口
                    AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition) candidateComponent;
                    AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();
                    Assert.isTrue(annotationMetadata.isInterface(),"@FeignClient can only be specified on an interface");
                    Map<String, Object> attributes = annotationMetadata.getAnnotationAttributes(FeignClient.class.getCanonicalName());
                    String name = getClientName(attributes);
                    //注册客户端配置
                    registerClientConfiguration(registry, name, attributes.get("configuration"));
                    //注册 FeignClient
                    registerFeignClient(registry, annotationMetadata, attributes);
                }
            }
        }
    }

    private void registerFeignClient(BeanDefinitionRegistry registry,
            AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
        String className = annotationMetadata.getClassName();
        //将属性设置到 FeignClientFactoryBean 中
        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);
        String contextId = getContextId(attributes);
        definition.addPropertyValue("contextId", contextId);
        definition.addPropertyValue("type", className);
        definition.addPropertyValue("decode404", attributes.get("decode404"));
        definition.addPropertyValue("fallback", attributes.get("fallback"));
        definition.addPropertyValue("fallbackFactory", attributes.get("fallbackFactory"));
        //设置 Autowire类型
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);

        String alias = contextId + "FeignClient";
        AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
        beanDefinition.setAttribute(FactoryBean.OBJECT_TYPE_ATTRIBUTE, className);

        // has a default, won‘t be null
        boolean primary = (Boolean) attributes.get("primary");

        beanDefinition.setPrimary(primary);

        String qualifier = getQualifier(attributes);
        if (StringUtils.hasText(qualifier)) {
            alias = qualifier;
        }
        //注册 BeanDefinition
        BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, new String[] { alias });
        BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
    }
}

@RestController
@RequestMapping("/test")
public class TestController {

    @Autowired
    FeignService feignService;

    @RequestMapping("/getString")
    public String getStr(){
        return feignService.getName();
    }
}

class FeignClientFactoryBean implements FactoryBean<Object>, InitializingBean, ApplicationContextAware {


    @Override
    public Object getObject() throws Exception {
        return getTarget();
    }

    <T> T getTarget() {
        FeignContext context = applicationContext.getBean(FeignContext.class);
        Feign.Builder builder = feign(context);

        if (!StringUtils.hasText(url)) {
            if (!name.startsWith("http")) {
                url = "http://" + name;
            }
            else {
                url = name;
            }
            url += cleanPath();
            return (T) loadBalance(builder, context,
                    new HardCodedTarget<>(type, name, url));
        }
        if (StringUtils.hasText(url) && !url.startsWith("http")) {
            url = "http://" + 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();
            }
            if (client instanceof FeignBlockingLoadBalancerClient) {
                // not load balancing because we have a url,
                // but Spring Cloud LoadBalancer is on the classpath, so unwrap
                client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
            }
            builder.client(client);
        }
        Targeter targeter = get(context, Targeter.class);
        return (T) targeter.target(this, builder, context,
                new HardCodedTarget<>(type, name, url));
    }
    protected Feign.Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(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))
                .contract(get(context, Contract.class));
        // @formatter:on

        configureFeign(context, builder);

        return builder;
    }
　　// 获取 Targeter 
    protected <T> T get(FeignContext context, Class<T> type) {
        T instance = context.getInstance(contextId, type);
        if (instance == null) {
            throw new IllegalStateException(
                    "No bean found of type " + type + " for " + contextId);
        }
        return instance;
    }
    
    protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
            HardCodedTarget<T> target) {
        Client client = getOptional(context, Client.class);
        if (client != null) {
            builder.client(client);
            Targeter targeter = get(context, Targeter.class);
            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?");
    }
}

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(Feign.class)
@EnableConfigurationProperties({ FeignClientProperties.class,
        FeignHttpClientProperties.class })
@Import(DefaultGzipDecoderConfiguration.class)
public class FeignAutoConfiguration {

    //如果配置了 feign.hystrix.HystrixFeign属性则加载此配置
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(name = "feign.hystrix.HystrixFeign")
    protected static class HystrixFeignTargeterConfiguration {

        @Bean
        @ConditionalOnMissingBean
        public Targeter feignTargeter() {
            return new HystrixTargeter();
        }
    }
    
    //如果没有配置 feign.hystrix.HystrixFeign属性则加载此配置
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnMissingClass("feign.hystrix.HystrixFeign")
    protected static class DefaultFeignTargeterConfiguration {

        @Bean
        @ConditionalOnMissingBean
        public Targeter feignTargeter() {
            return new DefaultTargeter();
        }
    }
}

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ HystrixCommand.class, HystrixFeign.class })
protected static class HystrixFeignConfiguration {

    @Bean
    @Scope("prototype")
    @ConditionalOnMissingBean
    @ConditionalOnProperty(name = "feign.hystrix.enabled")
    public Feign.Builder feignHystrixBuilder() {
        return HystrixFeign.builder();
    }
}

class HystrixTargeter implements Targeter {

    @Override
    public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
            FeignContext context, Target.HardCodedTarget<T> target) {
        if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
            return feign.target(target);
        }
        feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign;
        String name = StringUtils.isEmpty(factory.getContextId()) ? factory.getName()
                : factory.getContextId();
        SetterFactory setterFactory = getOptional(name, context, SetterFactory.class);
        if (setterFactory != null) {
            builder.setterFactory(setterFactory);
        }
        Class<?> fallback = factory.getFallback();
        if (fallback != void.class) {
　　　　　　　// 如果有配置 fallback
            return targetWithFallback(name, context, target, builder, fallback);
        }
        Class<?> fallbackFactory = factory.getFallbackFactory();
        if (fallbackFactory != void.class) {
　　　　　　  // 如果有配置 fallBackFactory 
            return targetWithFallbackFactory(name, context, target, builder, fallbackFactory);
        }

        return feign.target(target);
    }
}

public final class HystrixFeign {    
    
    public <T> T target(Target<T> target, T fallback) {
      return build(fallback != null ? new FallbackFactory.Default<T>(fallback) : null)
          .newInstance(target);
    }

    public <T> T target(Target<T> target, FallbackFactory<? extends T> fallbackFactory) {
　　　　// 最终是在ReflectiveFeign 实现.
      return build(fallbackFactory).newInstance(target);
    }
    
    Feign build(final FallbackFactory<?> nullableFallbackFactory) {
      super.invocationHandlerFactory(new InvocationHandlerFactory() {
        @Override
        public InvocationHandler create(Target target,
                                        Map<Method, MethodHandler> dispatch) {
          return new HystrixInvocationHandler(target, dispatch, setterFactory,
              nullableFallbackFactory);
        }
      });
      super.contract(new HystrixDelegatingContract(contract));
      return super.build();
    }
}

final class HystrixInvocationHandler implements InvocationHandler {

  private final Target<?> target;
  private final Map<Method, MethodHandler> dispatch;
  private final FallbackFactory<?> fallbackFactory; // Nullable
  private final Map<Method, Method> fallbackMethodMap;
  private final Map<Method, Setter> setterMethodMap;

  HystrixInvocationHandler(Target<?> target, Map<Method, MethodHandler> dispatch,
      SetterFactory setterFactory, FallbackFactory<?> fallbackFactory) {
    this.target = checkNotNull(target, "target");
    this.dispatch = checkNotNull(dispatch, "dispatch");
    this.fallbackFactory = fallbackFactory;
    this.fallbackMethodMap = toFallbackMethod(dispatch);
    this.setterMethodMap = toSetters(setterFactory, target, dispatch.keySet());
  }
  
    @Override
  public Object invoke(final Object proxy, final Method method, final Object[] args)
      throws Throwable {
    // early exit if the invoked method is from java.lang.Object
    // code is the same as ReflectiveFeign.FeignInvocationHandler
    if ("equals".equals(method.getName())) {
      try {
        Object otherHandler =
            args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
        return equals(otherHandler);
      } catch (IllegalArgumentException e) {
        return false;
      }
    } else if ("hashCode".equals(method.getName())) {
      return hashCode();
    } else if ("toString".equals(method.getName())) {
      return toString();
    }

    HystrixCommand<Object> hystrixCommand =
        new HystrixCommand<Object>(setterMethodMap.get(method)) {
          @Override
          protected Object run() throws Exception {
            try {
              return HystrixInvocationHandler.this.dispatch.get(method).invoke(args);
            } catch (Exception e) {
              throw e;
            } catch (Throwable t) {
              throw (Error) t;
            }
          }

          @Override
          protected Object getFallback() {
            if (fallbackFactory == null) {
              return super.getFallback();
            }
            try {
              Object fallback = fallbackFactory.create(getExecutionException());
              Object result = fallbackMethodMap.get(method).invoke(fallback, args);
              ...省略
    return hystrixCommand.execute();
  }
}

public Feign build() {
      Client client = Capability.enrich(this.client, capabilities);
      Retryer retryer = Capability.enrich(this.retryer, capabilities);
      List<RequestInterceptor> requestInterceptors = this.requestInterceptors.stream()
          .map(ri -> Capability.enrich(ri, capabilities))
          .collect(Collectors.toList());
      Logger logger = Capability.enrich(this.logger, capabilities);
      Contract contract = Capability.enrich(this.contract, capabilities);
      Options options = Capability.enrich(this.options, capabilities);
      Encoder encoder = Capability.enrich(this.encoder, capabilities);
      Decoder decoder = Capability.enrich(this.decoder, capabilities);
      InvocationHandlerFactory invocationHandlerFactory =
          Capability.enrich(this.invocationHandlerFactory, capabilities);
      QueryMapEncoder queryMapEncoder = Capability.enrich(this.queryMapEncoder, capabilities);

      SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
          new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
              logLevel, decode404, closeAfterDecode, propagationPolicy, forceDecoding);
      ParseHandlersByName handlersByName =
          new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder,
              errorDecoder, synchronousMethodHandlerFactory);
      return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);
    }

public class ReflectiveFeign extends Feign {

  private final ParseHandlersByName targetToHandlersByName;
  private final InvocationHandlerFactory factory;
  private final QueryMapEncoder queryMapEncoder;

  ReflectiveFeign(ParseHandlersByName targetToHandlersByName, InvocationHandlerFactory factory,
      QueryMapEncoder queryMapEncoder) {
    this.targetToHandlersByName = targetToHandlersByName;
    this.factory = factory;
    this.queryMapEncoder = queryMapEncoder;
  }
  
  
  @Override
  public <T> T newInstance(Target<T> target) {
    Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
    Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
    List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();

    for (Method method : target.type().getMethods()) {
      if (method.getDeclaringClass() == Object.class) {
        continue;
      } 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)));
      }
    }
    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;
  }
}