Spring Cloud OpenFeign 源码解析

0. 入门demo

• 此代码是 OpenFeign 的示例代码，获取一个Github 仓库的所有贡献者，创建一个issue。 建议由此开始 DEBUG 调试阅读源码

interface GitHub {
  @RequestLine("GET /repos/{owner}/{repo}/contributors")
  List<Contributor> contributors(@Param("owner") String owner, @Param("repo") String repo);

  @RequestLine("POST /repos/{owner}/{repo}/issues")
  void createIssue(Issue issue, @Param("owner") String owner, @Param("repo") String repo);

}

public static class Contributor {
  String login;
  int contributions;
}

public static class Issue {
  String title;
  String body;
  List<String> assignees;
  int milestone;
  List<String> labels;
}

public class MyApp {
  public static void main(String... args) {
    GitHub github = Feign.builder()
                         .decoder(new GsonDecoder())
                         .target(GitHub.class, "https://api.github.com");
  
    // Fetch and print a list of the contributors to this library.
    List<Contributor> contributors = github.contributors("OpenFeign", "feign");
    for (Contributor contributor : contributors) {
      System.out.println(contributor.login + " (" + contributor.contributions + ")");
    }
  }
}

Feign.build 注入依赖配置项

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

调用JDK动态代理生成接口代理类

动态代理生成接口对象

public class ReflectiveFeign extends Feign {
    @Override
    public <T> T newInstance(Target<T> target) {
        //使用Contract解析接口类上的方法和注解，转换单独MethodHandler处理
        Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
        // 使用DK动态代理为接口生成代理对象，实际业务逻辑交给 InvocationHandler 处理，其实就是调用 MethodHandler 
        InvocationHandler handler = factory.create(target, methodToHandler);
        T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class<?>[]{target.type()}, handler);
        return proxy;
    }
}

解析接口方法注解信息

• 如何解析上文 Demo 中 Github.contributors 方法的注解信息呢。 Feign中提供一个Contract 解析协议，有如下实现。
  

默认支持解析逻辑

class Default extends Contract.BaseContract {
    protected void processAnnotationOnMethod(MethodMetadata data, Annotation methodAnnotation, Method method) {
        Class<? extends Annotation> annotationType = methodAnnotation.annotationType();
        if (annotationType == RequestLine.class) {
            //@RequestLine    注解处理逻辑
        } else if (annotationType == Body.class) {
            //@Body    注解处理逻辑
        } else if (annotationType == Headers.class) {
            //@Headers    注解处理逻辑
        }
    }
    protected boolean processAnnotationsOnParameter(MethodMetadata data, Annotation[] annotations, int paramIndex) {
        boolean isHttpAnnotation = false;
        for (Annotation annotation : annotations) {
            Class<? extends Annotation> annotationType = annotation.annotationType();
            if (annotationType == Param.class) {
                Param paramAnnotation = (Param) annotation;
                //@Param    注解处理逻辑
            } else if (annotationType == QueryMap.class) {
                //@QueryMap    注解处理逻辑
            } else if (annotationType == HeaderMap.class) {
                //@HeaderMap    注解处理逻辑
            }
        }
        return isHttpAnnotation;
    }
}

原生的常用注解

Annotation	Interface Target
@RequestLine	Method
@Param	Parameter
@Headers	Method, Type
@QueryMap	Parameter
@HeaderMap	Parameter
@Body	Method

Spring MVC 扩展注解

• SpringMvcContract 为 spring-cloud-open-feign 的扩展支持SpringMVC注解，现 feign 版本也已支持

public class SpringMvcContract  {
    
    // 处理类上的 @RequestMapping
    @Override
    protected void processAnnotationOnClass(MethodMetadata data, Class<?> clz) {
        if (clz.getInterfaces().length == 0) {
            RequestMapping classAnnotation = findMergedAnnotation(clz,
                    RequestMapping.class);
        }
    }
    
    // 处理 @RequestMapping 注解，当然也支持衍生注解 @GetMapping @PostMapping 等处理
    @Override
    protected void processAnnotationOnMethod(MethodMetadata data,
                                             Annotation methodAnnotation, Method method) {
        if (!RequestMapping.class.isInstance(methodAnnotation) && !methodAnnotation
                .annotationType().isAnnotationPresent(RequestMapping.class)) {
            return;
        }
        RequestMapping methodMapping = findMergedAnnotation(method, RequestMapping.class);
        // 获取请求方法
        RequestMethod[] methods = methodMapping.method();
        // produce处理
        parseProduces(data, method, methodMapping);
        // consumes处理
        parseConsumes(data, method, methodMapping);
        // headers头处理
        parseHeaders(data, method, methodMapping);

        data.indexToExpander(new LinkedHashMap<Integer, Param.Expander>());
    }

    // 处理 请求参数 SpringMVC 原生注解
    @Override
    protected boolean processAnnotationsOnParameter(MethodMetadata data,
                                                    Annotation[] annotations, int paramIndex) {
        Param.Expander expander = this.convertingExpanderFactory
                .getExpander(typeDescriptor);
        if (expander != null) {
            data.indexToExpander().put(paramIndex, expander);
        }
        return isHttpAnnotation;
    }
}

MethodHandler 请求处理逻辑

MethodHandler 路由

如上图， 根据不同的请求方法路由到不同的 MethodHandler 实现

final class SynchronousMethodHandler implements MethodHandler {
    @Override
    public Object invoke(Object[] argv) throws Throwable {
        // 获取请求模板
        RequestTemplate template = buildTemplateFromArgs.create(argv);
        // 参数处理
        Options options = findOptions(argv);
        // 默认的重试器
        Retryer retryer = this.retryer.clone();
        while (true) {
            try {
                // 执行请求拦截器
                Request request = targetRequest(template);
                // 输出请求报文
                if (logLevel != Logger.Level.NONE) {
                    logger.logRequest(metadata.configKey(), logLevel, request);
                }
                Response response = client.execute(request, options);
                // 根据返回的状态码 ，做 Decode 处理
                ...
                return response;
            } catch (RetryableException e) {
                // 执行重试的相关逻辑
            }
        }
    }
}

根据不同参数构建请求模板

• 表单提交 、还是直接body 提交

执行请求拦截器生成最终Request

// 获取全部的请求拦截器，一个个执行
  Request targetRequest(RequestTemplate template) {
    for (RequestInterceptor interceptor : requestInterceptors) {
      interceptor.apply(template);
    }
    return target.apply(template);
  }

请求日志处理

• 日志输出级别，配置

public enum Level {
    /**
     * 不输出
     */
    NONE,
    /**
     * 只记录输出Http 方法、URL、状态码、执行时间
     */
    BASIC,
    /**
     * 输出请求头 和 Http 方法、URL、状态码、执行时间
     */
    HEADERS,
    /**
     * 输出请求头、报文体 和 Http 方法、URL、状态码、执行时间
     */
    FULL
}

Client 执行最终的Requst 请求

默认default 处理

• 通过JDK 的 java.net包 实现，没请求都会创建连接实现。可以配置成 HttpClient 或者 OKHttp 的高性能实现

class Default implements Client {

    private final SSLSocketFactory sslContextFactory;
    private final HostnameVerifier hostnameVerifier;
    
    @Override
    public Response execute(Request request, Request.Options options) throws IOException {
        HttpURLConnection connection = convertAndSend(request, options);
        return convertResponse(connection, request);
    }
」

Spring Cloud 的负载均衡处理

// Spring Cloud 的Client 实现
public class FeignBlockingLoadBalancerClient {
    @Override
    public Response execute(Request request, Request.Options options) throws IOException {
        // 例如请求： http://pig-auth-server/token/info
        final URI originalUri = URI.create(request.url());
        // 截取到serviceId: pig-auth-server
        String serviceId = originalUri.getHost();
        // 调用 loadBalancer API 获取到可以的服务实例
        ServiceInstance instance = loadBalancerClient.choose(serviceId);
        // 构建真实的请求URL http://172.17.0.110:8763/token/info
        String reconstructedUrl = loadBalancerClient.reconstructURI(instance, originalUri)
                .toString();
        // 创建请求 并执行
        Request newRequest = Request.create(request.httpMethod(), reconstructedUrl,
                request.headers(), request.requestBody());
        return delegate.execute(newRequest, options);
    }
}

返回报文Decoder 处理

• 默认处理

  class Default implements Encoder {

    @Override
    public void encode(Object object, Type bodyType, RequestTemplate template) {
      if (bodyType == String.class) {
        template.body(object.toString());
      } else if (bodyType == byte[].class) {
        template.body((byte[]) object, null);
      } else if (object != null) {
        throw new EncodeException(
            format("%s is not a type supported by this encoder.", object.getClass()));
      }
    }
  }

• 若是返回报文报错处理

  public static class Default implements ErrorDecoder {

    private final RetryAfterDecoder retryAfterDecoder = new RetryAfterDecoder();

    @Override
    public Exception decode(String methodKey, Response response) {
      FeignException exception = errorStatus(methodKey, response);
      Date retryAfter = retryAfterDecoder.apply(firstOrNull(response.headers(), RETRY_AFTER));
      if (retryAfter != null) {
        return new RetryableException(
            response.status(),
            exception.getMessage(),
            response.request().httpMethod(),
            exception,
            retryAfter,
            response.request());
      }
      return exception;
    }

    private <T> T firstOrNull(Map<String, Collection<T>> map, String key) {
      if (map.containsKey(key) && !map.get(key).isEmpty()) {
        return map.get(key).iterator().next();
      }
      return null;
    }
  }
}

注入 自定义的 ErrorDecoder 比较常用。

以上内容为 OpenFeign 的请求处理流程，下面为扩展内容 spring-cloud-open-feign 是如何初始化及其运行的呢?

【扩展】 Spring Cloud OpenFeign

EnableFeignClients 解析

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

• 当我们在 Main 方法，加上 @EnableFeignClients 注解，则开启了 spring-cloud-open-feign的相关功能。
• Import(FeignClientsRegistrar.class) 导入FeignClientsRegistrar,扫描 @FeignClient 注入到容器

FeignClientsRegistrar

class FeignClientsRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata,
                                        BeanDefinitionRegistry registry) {
        registerFeignClients(metadata, registry);
    }
    
    public void registerFeignClients(AnnotationMetadata metadata,
                                     BeanDefinitionRegistry registry) {
        
        // 扫描配置注解中配置范围内的 @FeignClient
        for (String basePackage : basePackages) {
            // 注入IOC 容器
            registerClientConfiguration(registry, name,
                            attributes.get("configuration"));
        }
    }
    
    //feignclient <--> bean 构造
    private void registerFeignClient(BeanDefinitionRegistry registry,
                                     AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
        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);
        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"));
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
        ...

        BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className,
                new String[] { alias });
        BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
    }
}

默认情况

public class FeignAutoConfiguration {
    // 未引入 feign-hystrix 模块，则还是注入 DefaultTargeter
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnMissingClass("feign.hystrix.HystrixFeign")
    protected static class DefaultFeignTargeterConfiguration {
    
        @Bean
        @ConditionalOnMissingBean
        public Targeter feignTargeter() {
            return new DefaultTargeter();
        }
    }
}

未引入 feign-hystrix 则还是上文的流程就同最初的流程一致 ， 我们在调用 feignclient.method 会触发动态代理,执行 MethodHandler 的逻辑

HystrixFeign

• 首先，引入了 HystrixFeign，是不是意味逻辑变得更了呢

最初 0. 入门Demo Feign.builder(),就变成了 HystrixFeign.builder()

public final class HystrixFeign {
    public static Builder builder() {
        return new Builder();
    }
    public static final class Builder extends Feign.Builder {
        
        // 注入 HystrixInvocationHandler 的实现
        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();
        }
        
    }
}

• 注入 HystrixInvocationHandler 的实现，使用HystrixCommand 包装，最终还是使用methodhandler 去调用最终的接口

final class HystrixInvocationHandler implements InvocationHandler {
    
    @Override
    public Object invoke(final Object proxy, final Method method, final Object[] args)
            throws Throwable {

        // 使用HystrixCommand 包装
        HystrixCommand<Object> hystrixCommand =
                new HystrixCommand<Object>(setterMethodMap.get(method)) {
                    @Override
                    protected Object run() throws Exception {
                        try {
                            // 调用 methodhandler 处理最终的请求
                            return HystrixInvocationHandler.this.dispatch.get(method).invoke(args);
                        } catch (Exception e) {
                            throw e;
                        } catch (Throwable t) {
                            throw (Error) t;
                        }
                    }
                };


        return hystrixCommand.execute();
    }
}

SentinelFeign

• 先看类注释 like {@link HystrixFeign.Builder} ，"借鉴" HystrixFeign

/**
 * {@link Feign.Builder} like {@link HystrixFeign.Builder}.
 */
public final class SentinelFeign {
}

• 注入 SentinelInvocationHandler 的实现，使用Sentinel包装，最终还是使用methodhandler 去调用最终的接口

public class SentinelInvocationHandler implements InvocationHandler {
    @Override
    public Object invoke(final Object proxy, final Method method, final Object[] args)
            throws Throwable {
        // 使用sentinel 包装请求
        try {
            ContextUtil.enter(resourceName);
            entry = SphU.entry(resourceName, EntryType.OUT, 1, args);
            result = methodHandler.invoke(args);
        }
        catch (Throwable ex) {
            // fallback 逻辑
        }
        finally {
            ContextUtil.exit();
        }
        return result;
    }
}

总结时序图

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