spring cloud openfeign源码分析

大体流程鱼骨图

 1.读取配置

　启动类上添加注解@EnableFeignClients，工程启动后会自动读取注解上的配置

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

这里我们可以看到 EnableFeignClients 注解引入了配置类 org.springframework.cloud.openfeign.FeignClientsRegistrar

registerBeanDefinitions方法提供了注册 EnableFeignClients注解信息和 FeignClient信息的功能

@Override
    public void registerBeanDefinitions(AnnotationMetadata metadata,
            BeanDefinitionRegistry registry) {
        registerDefaultConfiguration(metadata, registry);
        registerFeignClients(metadata, registry);
    }

 拼接注解信息放在 definition中，然后交给spring容器管理

org.springframework.cloud.openfeign.FeignClientsRegistrar#registerFeignClients

private void registerFeignClient(BeanDefinitionRegistry registry,
            AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
        String className = annotationMetadata.getClassName();
                //根据工厂类获得对象
        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);

        String alias = contextId + "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);
    }        

　

2.创建代理实例方法

feign.ReflectiveFeign#newInstance

  public <T> T newInstance(Target<T> target) {
        Map<String, MethodHandler> nameToHandler = this.targetToHandlersByName.apply(target);
        Map<Method, MethodHandler> methodToHandler = new LinkedHashMap();
        List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList();
        Method[] var5 = target.type().getMethods();
        int var6 = var5.length;

        for(int var7 = 0; var7 < var6; ++var7) {
            Method method = var5[var7];
            if (method.getDeclaringClass() != Object.class) {
                if (Util.isDefault(method)) {
                    DefaultMethodHandler handler = new DefaultMethodHandler(method);
                    defaultMethodHandlers.add(handler);
                    methodToHandler.put(method, handler);
                } else {
                    methodToHandler.put(method, (MethodHandler)nameToHandler.get(Feign.configKey(target.type(), method)));
                }
            }
        }
　　　　 //在这里我们可以看到feign创建了一个代理类
        InvocationHandler handler = this.factory.create(target, methodToHandler);
        T proxy = Proxy.newProxyInstance(target.type().getClassLoader(), new Class[]{target.type()}, handler);
        Iterator var12 = defaultMethodHandlers.iterator();

        while(var12.hasNext()) {
            DefaultMethodHandler defaultMethodHandler = (DefaultMethodHandler)var12.next();
            defaultMethodHandler.bindTo(proxy);
        }

        return proxy;
    }

创建代理类的方法

        public InvocationHandler create(Target target, Map<Method, InvocationHandlerFactory.MethodHandler> dispatch) {
            return new FeignInvocationHandler(target, dispatch);
        }
    }

代理类的invoke方法，feign.ReflectiveFeign.FeignInvocationHandler#invoke

 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if (!"equals".equals(method.getName())) {
                if ("hashCode".equals(method.getName())) {
                    return this.hashCode();
                } else {
                    return "toString".equals(method.getName()) ? this.toString() : ((MethodHandler)this.dispatch.get(method)).invoke(args);
                }
            } else {
                try {
                    Object otherHandler = args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
                    return this.equals(otherHandler);
                } catch (IllegalArgumentException var5) {
                    return false;
                }
            }
        }

查看上面的invoke方法是怎么实现的

    public interface MethodHandler {
        Object invoke(Object[] var1) throws Throwable;
    }

找到实现类 feign.SynchronousMethodHandler#invoke

 public Object invoke(Object[] argv) throws Throwable {
        //这里创建了一个template
        RequestTemplate template = this.buildTemplateFromArgs.create(argv);
        Options options = this.findOptions(argv);
        Retryer retryer = this.retryer.clone();

        while(true) {
            try {
    
                return this.executeAndDecode(template, options);
            } catch (RetryableException var9) {
                RetryableException e = var9;

                try {
                    retryer.continueOrPropagate(e);
                } catch (RetryableException var8) {
                    Throwable cause = var8.getCause();
                    if (this.propagationPolicy == ExceptionPropagationPolicy.UNWRAP && cause != null) {
                        throw cause;
                    }

                    throw var8;
                }

                if (this.logLevel != Level.NONE) {
                    this.logger.logRetry(this.metadata.configKey(), this.logLevel);
                }
            }
        }
    }        

 然后调用ribbon，执行rest请求 org.springframework.cloud.openfeign.ribbon.LoadBalancerFeignClient#execute

@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);
        }
    }

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大部分都是贴的源码，本文只是为了记录一次feign的大致实现思想，其中很多精妙的方式并没有提及