[microservice openfeign] @feignclient detailed explanation

Last one , We use sentinel Integrate feign, Have a preliminary understanding of both , This article , More focused on feign Use and details of .

The steps of integration are roughly the same as the former , Let's take a look first @FeignClient.

value/name

value and name It does the same thing , If not configured url Then the configured value will be the service name , For service discovery .

On the contrary, it's just a name .

If you also specify url and name/value , With url Subject to , name/value Will be the name of the service ,url Address for service .

serviceId

serviceId It's abandoned , Use it directly name that will do .

contextId

If I have two feignclient All have the same name , By specifying different contextId To distinguish between , Otherwise, there are two at the same time bean It's a mistake .

Of course , You can also configure spring.main.allow-bean-definition-overriding=true, The function is to allow beanName Same BeanDefinition.

Let's take a look at the source code ：

org.springframework.cloud.openfeign.FeignClientsRegistrar#getClientName

	private String getClientName(Map<String, Object> client) {
    
		if (client == null) {
    
			return null;
		}
		String value = (String) client.get("contextId");
		if (!StringUtils.hasText(value)) {
    
			value = (String) client.get("value");
		}
		if (!StringUtils.hasText(value)) {
    
			value = (String) client.get("name");
		}
		if (!StringUtils.hasText(value)) {
    
			value = (String) client.get("serviceId");
		}
		if (StringUtils.hasText(value)) {
    
			return value;
		}

		throw new IllegalStateException("Either 'name' or 'value' must be provided in @"
				+ FeignClient.class.getSimpleName());
	}

You can see that if it is configured contextId Will use contextId, If it's not configured, it will go value And then there was name And finally serviceId. No configuration by default , When a service has more than one Feign Client When it's time to report something wrong .

The second role is to register FeignClient in ,contextId Will act as Client Part of the alias , If the qualifier Give priority to qualifier As an alias .

	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);

		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;
		}

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

url

Used to configure the address of the specified service , It's equivalent to requesting the service directly , Service selection without load balancer .

decode404

When a call request occurs 404 When it's wrong ,decode404 The value of is true, Then it will execute decoder decode , Otherwise, throw an exception .

configuration

configuration It's configuration Feign Configuration class , In the configuration class, you can customize Feign Of Encoder、Decoder、LogLevel、Contract etc. .

fallback

Defines fault-tolerant handling classes , That is, fallback logic ,fallback Must implement Feign Client The interface of , It is impossible to know the abnormal information of fusing .

fallbackFactory

It's also fault-tolerant processing , We can know the abnormal information of the fuse .

path

path Define the current FeignClient Uniform prefixes for interfaces , For example, the interface address is /user/get, If you define the prefix as user, Then the path of the specific method only needs to write /get that will do , When we configure server.context-path,server.servlet-path When using .

primary

primary The corresponding is @Primary annotation , The default is true, There's also a reason for the official setting . When our Feign Realized fallback after , That means Feign Client There are several identical Bean stay Spring In the container , When we are using @Autowired When it comes to injection , I don't know which one to inject , So we need to set a high priority ,@Primary Annotation is what we do .

qualifier

qualifier The corresponding is @Qualifier annotation , General scene direct @Autowired Just inject it directly .

If our Feign Client Yes fallback Realization , Default @FeignClient Annotated primary=true, It means that we use @Autowired There is no problem with injection , Will give priority to your Feign Client.

If you are a ghost axe and a god sent one primary Set to false 了 , Direct use @Autowired The injection place will report an error , I don't know which object to inject .

The solution is obvious , You can take primary Set to true that will do , If for some special reason , You have to get rid of primary=true Set up , How do we inject in this case , We can configure a qualifier, And then use @Qualifier Annotations are injected .