Feign's overall process

1. Feign The overall process of
   1. effect
   2. Overall process
      1. FeignClientsRegistrar Of registerFeignClient() Method
      2. getTarget() Method
      3. Creation of dynamic agents
   3. summary

Feign The overall process of

effect

feign Is the basis RPC The interface called remotely generates a dynamic proxy instance , And then according to SpringMVC Annotation generation method processor on Method in , The resulting HTTP request , adopt feignClient Send it to the server .

Overall process

feign The overall process of ：

FeignClientsRegistrar Of registerFeignClient() Method

Add comments to the startup class @EnableFeignClients, This annotation imports FeignClientsRegistrar class ,FeignClientsRegistrar The main function of class is to scan @FeignClient Annotation creation FeignClientFactoryBean example , Then inject into Spring In the container .

private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {        String className = annotationMetadata.getClassName();        BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(FeignClientFactoryBean.class);        this.validate(attributes);        definition.addPropertyValue("url", this.getUrl(attributes));        definition.addPropertyValue("path", this.getPath(attributes));        String name = this.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(2);        String alias = name + "FeignClient";        AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();        boolean primary = (Boolean)attributes.get("primary");        beanDefinition.setPrimary(primary);        String qualifier = this.getQualifier(attributes);        if (StringUtils.hasText(qualifier)) {            alias = qualifier;        }        BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, new String[]{alias});        BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);    }

getTarget() Method

Then the code passes @Resource When annotations are used , Will pass FeignClientFactoryBean Of getObject() Method to get the dynamic proxy object . Dynamic proxy objects are generated by Feign.Builder Of target Call in method build（） Method generation ReflectiveFeign Example , And then through newInstance Create the final RPC An instance of a dynamic proxy .

<T> T getTarget() {        FeignContext context = (FeignContext)this.applicationContext.getBean(FeignContext.class);        Builder builder = this.feign(context);        String url;        if (!StringUtils.hasText(this.url)) {            if (!this.name.startsWith("http")) {                url = "http://" + this.name;            } else {                url = this.name;            }            url = url + this.cleanPath();            return this.loadBalance(builder, context, new HardCodedTarget(this.type, this.name, url));        } else {            if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {                this.url = "http://" + this.url;            }            url = this.url + this.cleanPath();            Client client = (Client)this.getOptional(context, Client.class);            if (client != null) {                if (client instanceof LoadBalancerFeignClient) {                    client = ((LoadBalancerFeignClient)client).getDelegate();                }                builder.client(client);            }            Targeter targeter = (Targeter)this.get(context, Targeter.class);            return targeter.target(this, builder, context, new HardCodedTarget(this.type, this.name, url));        }    }

Creation of dynamic agents

When creating a dynamic proxy instance ,feign You will first create a call processor , Then each method creates a method handler , The method processor is cached in the calling processor dispatch Collection . When a dynamic proxy instance makes a method call ,Feign According to the reflection instance, call the processor from dispatch Find the corresponding method processor in the collection , Then proceed Http request . Method processor generates Request request , And then to feign Call from the client of , Use it when you really use it LoadBalancerFeignClient, Because it can carry out load balancing , It also delegates specific client complete http request .

summary

This article mainly talks about Feign The overall process of , Mainly through @EnableFeignClients Annotation introduction FeignClientsRegistrar class , Scan in class @FeignClient annotation , Inject FeignClientFactoryBean example , adopt getObject() Method to get a dynamic instance ,Feign The remote call of is actually completed through dynamic proxy , The creation of dynamic proxy is feign Create proxy objects based on the reflection mechanism , Then find the corresponding method processor to launch http request