深入理解Feign之源码解析

谁践踏了优雅 2022-05-23 11:05 208阅读 0赞

# 深入理解Feign之源码解析 #

> 本文出自[方志朋的博客][Link 1]

## 什么是Feign ##

Feign是受到Retrofit，JAXRS-2.0和WebSocket的影响，它是一个jav的到http客户端绑定的开源项目。 Feign的主要目标是将Java Http 客户端变得简单。Feign的源码地址：[https://github.com/OpenFeign/feign][https_github.com_OpenFeign_feign]

## 写一个Feign ##

在我之前的博文有写到如何用Feign去消费服务，文章地址：[http://blog.csdn.net/forezp/article/details/69808079][http_blog.csdn.net_forezp_article_details_69808079] 。

现在来简单的实现一个Feign客户端，首先通过@FeignClient，客户端，其中value为调用其他服务的名称，FeignConfig.class为FeignClient的配置文件，代码如下：

@FeignClient(value = "service-hi",configuration = FeignConfig.class)
    public interface SchedualServiceHi {
        @GetMapping(value = "/hi")
        String sayHiFromClientOne(@RequestParam(value = "name") String name);
    }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7

其自定义配置文件如下，当然也可以不写配置文件，用默认的即可：

@Configuration
    public class FeignConfig { 
    
        @Bean
        public Retryer feignRetryer() {
            return new Retryer.Default(100, SECONDS.toMillis(1), 5);
        }
    
    }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11

查看FeignClient注解的源码，其代码如下：

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface FeignClient { 
    
    @AliasFor("name")
    String value() default "";
    
    @AliasFor("value")
    String name() default "";
    
    @AliasFor("value")
    String name() default "";
    String url() default "";
    boolean decode404() default false;
    
    Class<?>[] configuration() default {};
    Class<?> fallback() default void.class;
    
    Class<?> fallbackFactory() default void.class;
    }
    
    String path() default "";
    
    boolean primary() default true;

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19
 *  20
 *  21
 *  22
 *  23
 *  24
 *  25
 *  26
 *  27

FeignClient注解被@Target(ElementType.TYPE)修饰，表示FeignClient注解的作用目标在接口上；   
@Retention(RetentionPolicy.RUNTIME)，注解会在class字节码文件中存在，在运行时可以通过反射获取到；@Documented表示该注解将被包含在javadoc中。

feign 用于声明具有该接口的REST客户端的接口的注释应该是创建（例如用于自动连接到另一个组件。 如果功能区可用，那将是   
用于负载平衡后端请求，并且可以配置负载平衡器   
使用与伪装客户端相同名称（即值）@RibbonClient 。

其中value()和name()一样，是被调用的 service的名称。   
url(),直接填写硬编码的url,decode404()即404是否被解码，还是抛异常；configuration()，标明FeignClient的配置类，默认的配置类为FeignClientsConfiguration类，可以覆盖Decoder、Encoder和Contract等信息，进行自定义配置。fallback(),填写熔断器的信息类。

## FeignClient的配置 ##

默认的配置类为FeignClientsConfiguration，这个类在spring-cloud-netflix-core的jar包下，打开这个类，可以发现它是一个配置类，注入了很多的相关配置的bean，包括feignRetryer、FeignLoggerFactory、FormattingConversionService等,其中还包括了Decoder、Encoder、Contract，如果这三个bean在没有注入的情况下，会自动注入默认的配置。

*  Decoder feignDecoder: ResponseEntityDecoder(这是对SpringDecoder的封装)
 *  Encoder feignEncoder: SpringEncoder
 *  Logger feignLogger: Slf4jLogger
 *  Contract feignContract: SpringMvcContract
 *  Feign.Builder feignBuilder: HystrixFeign.Builder

代码如下：

@Configuration
    public class FeignClientsConfiguration { 
    
    ...//省略代码
    
    @Bean
        @ConditionalOnMissingBean
        public Decoder feignDecoder() {
            return new ResponseEntityDecoder(new SpringDecoder(this.messageConverters));
        }
    
        @Bean
        @ConditionalOnMissingBean
        public Encoder feignEncoder() {
            return new SpringEncoder(this.messageConverters);
        }
    
        @Bean
        @ConditionalOnMissingBean
        public Contract feignContract(ConversionService feignConversionService) {
            return new SpringMvcContract(this.parameterProcessors, feignConversionService);
        }
    
    ...//省略代码
    }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19
 *  20
 *  21
 *  22
 *  23
 *  24
 *  25
 *  26
 *  27

重写配置：

你可以重写FeignClientsConfiguration中的bean，从而达到自定义配置的目的，比如FeignClientsConfiguration的默认重试次数为Retryer.NEVER\_RETRY，即不重试，那么希望做到重写，写个配置文件，注入feignRetryer的bean,代码如下：

@Configuration
    public class FeignConfig { 
    
        @Bean
        public Retryer feignRetryer() {
            return new Retryer.Default(100, SECONDS.toMillis(1), 5);
        }
    
    }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10

在上述代码更改了该FeignClient的重试次数，重试间隔为100ms，最大重试时间为1s,重试次数为5次。

## Feign的工作原理 ##

feign是一个伪客户端，即它不做任何的请求处理。Feign通过处理注解生成request，从而实现简化HTTP API开发的目的，即开发人员可以使用注解的方式定制request api模板，在发送http request请求之前，feign通过处理注解的方式替换掉request模板中的参数，这种实现方式显得更为直接、可理解。

通过包扫描注入FeignClient的bean，该源码在FeignClientsRegistrar类：   
首先在启动配置上检查是否有@EnableFeignClients注解，如果有该注解，则开启包扫描，扫描被@FeignClient注解接口。代码如下：

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();
                }
                registerClientConfiguration(registry, name,
                        defaultAttrs.get("defaultConfiguration"));
            }
        }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19

程序启动后通过包扫描，当类有@FeignClient注解，将注解的信息取出，连同类名一起取出，赋给BeanDefinitionBuilder，然后根据BeanDefinitionBuilder得到beanDefinition，最后beanDefinition式注入到ioc容器中，源码如下：

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());
            AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(
                    FeignClient.class);
            final Class<?>[] clients = attrs == null ? null
                    : (Class<?>[]) attrs.get("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) {
                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");
    
                        Map<String, Object> attributes = annotationMetadata
                                .getAnnotationAttributes(
                                        FeignClient.class.getCanonicalName());
    
                        String name = getClientName(attributes);
                        registerClientConfiguration(registry, name,
                                attributes.get("configuration"));
    
                        registerFeignClient(registry, annotationMetadata, attributes);
                    }
                }
            }
        }
    
    
    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);
            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 });
            BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
        }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19
 *  20
 *  21
 *  22
 *  23
 *  24
 *  25
 *  26
 *  27
 *  28
 *  29
 *  30
 *  31
 *  32
 *  33
 *  34
 *  35
 *  36
 *  37
 *  38
 *  39
 *  40
 *  41
 *  42
 *  43
 *  44
 *  45
 *  46
 *  47
 *  48
 *  49
 *  50
 *  51
 *  52
 *  53
 *  54
 *  55
 *  56
 *  57
 *  58
 *  59
 *  60
 *  61
 *  62
 *  63
 *  64
 *  65
 *  66
 *  67
 *  68
 *  69
 *  70
 *  71
 *  72
 *  73
 *  74
 *  75
 *  76
 *  77
 *  78
 *  79
 *  80
 *  81
 *  82
 *  83
 *  84
 *  85
 *  86
 *  87
 *  88
 *  89
 *  90
 *  91
 *  92
 *  93
 *  94
 *  95
 *  96

注入bean之后，通过jdk的代理，当请求Feign Client的方法时会被拦截，代码在ReflectiveFeign类，代码如下：

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;
      }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19
 *  20
 *  21
 *  22
 *  23
 *  24
 *  25

在SynchronousMethodHandler类进行拦截处理，当被FeignClient的方法被拦截会根据参数生成RequestTemplate对象，该对象就是http请求的模板，代码如下：

@Override
      public Object invoke(Object[] argv) throws Throwable {
        RequestTemplate template = buildTemplateFromArgs.create(argv);
        Retryer retryer = this.retryer.clone();
        while (true) {
          try {
            return executeAndDecode(template);
          } catch (RetryableException e) {
            retryer.continueOrPropagate(e);
            if (logLevel != Logger.Level.NONE) {
              logger.logRetry(metadata.configKey(), logLevel);
            }
            continue;
          }
        }
      }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17

其中有个executeAndDecode()方法，该方法是通RequestTemplate生成Request请求对象，然后根据用client获取response。

Object executeAndDecode(RequestTemplate template) throws Throwable {
        Request request = targetRequest(template);
        ...//省略代码
        response = client.execute(request, options);
        ...//省略代码
    
    }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8

## Client组件 ##

其中Client组件是一个非常重要的组件，Feign最终发送request请求以及接收response响应，都是由Client组件完成的，其中Client的实现类，只要有Client.Default，该类由HttpURLConnnection实现网络请求，另外还支持HttpClient、Okhttp.

首先来看以下在FeignRibbonClient的自动配置类，FeignRibbonClientAutoConfiguration ，主要在工程启动的时候注入一些bean,其代码如下：

@ConditionalOnClass({ ILoadBalancer.class, Feign.class })
    @Configuration
    @AutoConfigureBefore(FeignAutoConfiguration.class)
    public class FeignRibbonClientAutoConfiguration { 
    
    @Bean
        @ConditionalOnMissingBean
        public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
                SpringClientFactory clientFactory) {
            return new LoadBalancerFeignClient(new Client.Default(null, null),
                    cachingFactory, clientFactory);
        }
    
    }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15

在缺失配置feignClient的情况下，会自动注入new Client.Default(),跟踪Client.Default()源码，它使用的网络请求框架为HttpURLConnection，代码如下：

@Override
        public Response execute(Request request, Options options) throws IOException {
          HttpURLConnection connection = convertAndSend(request, options);
          return convertResponse(connection).toBuilder().request(request).build();
        }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6

怎么在feign中使用HttpClient，查看FeignRibbonClientAutoConfiguration的源码

@ConditionalOnClass({ ILoadBalancer.class, Feign.class })
    @Configuration
    @AutoConfigureBefore(FeignAutoConfiguration.class)
    public class FeignRibbonClientAutoConfiguration {
    ...//省略代码
    
    @Configuration
        @ConditionalOnClass(ApacheHttpClient.class)
        @ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
        protected static class HttpClientFeignLoadBalancedConfiguration {
    
            @Autowired(required = false)
            private HttpClient httpClient;
    
            @Bean
            @ConditionalOnMissingBean(Client.class)
            public Client feignClient(CachingSpringLoadBalancerFactory cachingFactory,
                    SpringClientFactory clientFactory) {
                ApacheHttpClient delegate;
                if (this.httpClient != null) {
                    delegate = new ApacheHttpClient(this.httpClient);
                }
                else {
                    delegate = new ApacheHttpClient();
                }
                return new LoadBalancerFeignClient(delegate, cachingFactory, clientFactory);
            }
        }
    
    ...//省略代码
    }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19
 *  20
 *  21
 *  22
 *  23
 *  24
 *  25
 *  26
 *  27
 *  28
 *  29
 *  30
 *  31
 *  32

从代码@ConditionalOnClass(ApacheHttpClient.class)注解可知道，只需要在pom文件加上HttpClient的classpath就行了，另外需要在配置文件上加上feign.httpclient.enabled为true，从 @ConditionalOnProperty注解可知，这个可以不写，在默认的情况下就为true.

在pom文件加上：

<dependency>
        <groupId>com.netflix.feign</groupId>
        <artifactId>feign-httpclient</artifactId>
        <version>RELEASE</version>
    </dependency>

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7

同理，如果想要feign使用Okhttp，则只需要在pom文件上加上feign-okhttp的依赖：

<dependency>
        <groupId>com.netflix.feign</groupId>
        <artifactId>feign-okhttp</artifactId>
        <version>RELEASE</version>
    </dependency>

*  1
 *  2
 *  3
 *  4
 *  5
 *  6

## feign的负载均衡是怎么样实现的呢？ ##

通过上述的FeignRibbonClientAutoConfiguration类配置Client的类型(httpurlconnection，okhttp和httpclient)时候，可知最终向容器注入的是LoadBalancerFeignClient，即负载均衡客户端。现在来看下LoadBalancerFeignClient的代码：

@Override
        public Response execute(Request request, Request.Options options) throws IOException {
            try {
                URI asUri = URI.create(request.url());
                String clientName = asUri.getHost();
                URI uriWithoutHost = cleanUrl(request.url(), clientName);
                FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
                        this.delegate, request, uriWithoutHost);
    
                IClientConfig requestConfig = getClientConfig(options, clientName);
                return lbClient(clientName).executeWithLoadBalancer(ribbonRequest,
                        requestConfig).toResponse();
            }
            catch (ClientException e) {
                IOException io = findIOException(e);
                if (io != null) {
                    throw io;
                }
                throw new RuntimeException(e);
            }
        }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19
 *  20
 *  21

其中有个executeWithLoadBalancer()方法，即通过负载均衡的方式请求。

public T executeWithLoadBalancer(final S request, final IClientConfig requestConfig) throws ClientException {
            RequestSpecificRetryHandler handler = getRequestSpecificRetryHandler(request, requestConfig);
            LoadBalancerCommand<T> command = LoadBalancerCommand.<T>builder()
                    .withLoadBalancerContext(this)
                    .withRetryHandler(handler)
                    .withLoadBalancerURI(request.getUri())
                    .build();
    
            try {
                return command.submit(
                    new ServerOperation<T>() {
                        @Override
                        public Observable<T> call(Server server) {
                            URI finalUri = reconstructURIWithServer(server, request.getUri());
                            S requestForServer = (S) request.replaceUri(finalUri);
                            try {
                                return Observable.just(AbstractLoadBalancerAwareClient.this.execute(requestForServer, requestConfig));
                            } 
                            catch (Exception e) {
                                return Observable.error(e);
                            }
                        }
                    })
                    .toBlocking()
                    .single();
            } catch (Exception e) {
                Throwable t = e.getCause();
                if (t instanceof ClientException) {
                    throw (ClientException) t;
                } else {
                    throw new ClientException(e);
                }
            }
    
        }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15
 *  16
 *  17
 *  18
 *  19
 *  20
 *  21
 *  22
 *  23
 *  24
 *  25
 *  26
 *  27
 *  28
 *  29
 *  30
 *  31
 *  32
 *  33
 *  34
 *  35
 *  36

其中服务在submit()方法上，点击submit进入具体的方法,这个方法是LoadBalancerCommand的方法：

Observable<T> o = 
                    (server == null ? selectServer() : Observable.just(server))
                    .concatMap(new Func1<Server, Observable<T>>() {
                        @Override
                        // Called for each server being selected
                        public Observable<T> call(Server server) {
                            context.setServer(server);
    
            }}

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10

上述代码中有个selectServe()，该方法是选择服务的进行负载均衡的方法，代码如下：

private Observable<Server> selectServer() {
            return Observable.create(new OnSubscribe<Server>() {
                @Override
                public void call(Subscriber<? super Server> next) {
                    try {
                        Server server = loadBalancerContext.getServerFromLoadBalancer(loadBalancerURI, loadBalancerKey);   
                        next.onNext(server);
                        next.onCompleted();
                    } catch (Exception e) {
                        next.onError(e);
                    }
                }
            });
        }

*  1
 *  2
 *  3
 *  4
 *  5
 *  6
 *  7
 *  8
 *  9
 *  10
 *  11
 *  12
 *  13
 *  14
 *  15

最终负载均衡交给loadBalancerContext来处理，即之前讲述的Ribbon，在这里不再重复。

## 总结 ##

总到来说，Feign的源码实现的过程如下：

*  首先通过@EnableFeignCleints注解开启FeignCleint
 *  根据Feign的规则实现接口，并加@FeignCleint注解
 *  程序启动后，会进行包扫描，扫描所有的@ FeignCleint的注解的类，并将这些信息注入到ioc容器中。
 *  当接口的方法被调用，通过jdk的代理，来生成具体的RequesTemplate
 *  RequesTemplate在生成Request
 *  Request交给Client去处理，其中Client可以是HttpUrlConnection、HttpClient也可以是Okhttp
 *  最后Client被封装到LoadBalanceClient类，这个类结合类Ribbon做到了负载均衡。

## 参考资料 ##

[https://github.com/OpenFeign/feign][https_github.com_OpenFeign_feign]

[https://blog.de-swaef.eu/the-netflix-stack-using-spring-boot-part-3-feign/][https_blog.de-swaef.eu_the-netflix-stack-using-spring-boot-part-3-feign]

文章标签：   [java][] [源码][Link 2] [开源项目][Link 3]

个人分类：   [springcloud][]

所属专栏：   [史上最简单的 Spring Cloud 教程][Spring Cloud]

[Link 1]: http://blog.csdn.net/forezp
[https_github.com_OpenFeign_feign]: https://github.com/OpenFeign/feign
[http_blog.csdn.net_forezp_article_details_69808079]: http://blog.csdn.net/forezp/article/details/69808079
[https_blog.de-swaef.eu_the-netflix-stack-using-spring-boot-part-3-feign]: https://blog.de-swaef.eu/the-netflix-stack-using-spring-boot-part-3-feign/
[java]: http://so.csdn.net/so/search/s.do?q=java&t=blog
[Link 2]: http://so.csdn.net/so/search/s.do?q=%E6%BA%90%E7%A0%81&t=blog
[Link 3]: http://so.csdn.net/so/search/s.do?q=%E5%BC%80%E6%BA%90%E9%A1%B9%E7%9B%AE&t=blog
[springcloud]: https://blog.csdn.net/forezp/article/category/6830968
[Spring Cloud]: https://blog.csdn.net/column/details/15197.html