Shulou(Shulou.com)06/02 Report--

Today, I will talk to you about the role of FeignClientFactoryBean in Feign. Many people may not know much about it. In order to let everyone know more, Xiaobian summarizes the following contents for everyone. I hope you can gain something according to this article.

图1

其属性如List-1所示，这些属性的值都是在FeignClientsRegistrar中设置的。

List-1

class FeignClientFactoryBean implements FactoryBean, InitializingBean, ApplicationContextAware { /*********************************** * WARNING! Nothing in this class should be @Autowired. It causes NPEs because of some * lifecycle race condition. ***********************************/ private Class type; private String name; private String url; private String contextId; private String path; private boolean decode404; private ApplicationContext applicationContext; private Class fallback = void.class; private Class fallbackFactory = void.class;...

由于实现了FactoryBean接口，我们来看最重要的getObject()方法，如List-2，getTarget方法中首先从Spring上下文中获取FeignContext。FeignContext是在FeignAutoConfiguration中注册到Spring容器中的，如List-3所示，会将spring容器所有的FeignClientSpecification放入到FeignContext中，FeignClientSpecification在Feign源码分析之EnableFeignClients中讲过，即EnableFeignClients的defaultConfiguration。

List-2

@Overridepublic Object getObject() throws Exception { return getTarget();} T getTarget() { FeignContext context = this.applicationContext.getBean(FeignContext.class); Feign.Builder builder = feign(context);...

List-3

public class FeignAutoConfiguration { @Autowired(required = false) private List configurations = new ArrayList(); @Bean public HasFeatures feignFeature() { return HasFeatures.namedFeature("Feign", Feign.class); } @Bean public FeignContext feignContext() { FeignContext context = new FeignContext(); context.setConfigurations(this.configurations); return context; }...

List-2中，得到FeignContext后，调用feign方法，从FeignContext中获取Encoder、Decoder、Contract，其实内部是从spring容器中获取的，得到Feign.Builder。

我们可以实现RequestInterceptor接口，之后交给Spring容器，feign会自动加上这个拦截器，这个的实现也在FeignClientFactoryBean中，在configureUsingConfiguration方法中，如下List-4

List-4

Map requestInterceptors = context.getInstances(this.contextId, RequestInterceptor.class);if (requestInterceptors != null) { builder.requestInterceptors(requestInterceptors.values());}

List-4中的context.getInstances()方法内部是如何实现的呢。来看下FeignContext的父类NamedContextFactory，List-5中的setConfigurations方法在List-3中调用，在构造FeignContext的时候调用的。

List-5

public void setConfigurations(List configurations) { for (C client : configurations) { this.configurations.put(client.getName(), client); }}

List-6中

getConext方法获取ApplicationContext，之后从该ApplicationContext中获取bean

getConext方法中，如过name对应的ApplicationContext不存在，则调用createContext方法进行创建

AnnotationConfigApplicationContext.register方法把配置类注册到ApplicationContext中，还设置了AnnotationConfigApplicationContext的parent为当前Spring上下文，这样当在AnnotationConfigApplicationContext中获取不到bean时，就会从父ApplicationContext中获取

List-6

public T getInstance(String name, Class type) { AnnotationConfigApplicationContext context = getContext(name); if (BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context, type).length > 0) { return context.getBean(type); } return null;}protected AnnotationConfigApplicationContext getContext(String name) { if (!this.contexts.containsKey(name)) { synchronized (this.contexts) { if (!this.contexts.containsKey(name)) { this.contexts.put(name, createContext(name)); } } } return this.contexts.get(name);}protected AnnotationConfigApplicationContext createContext(String name) { AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(); if (this.configurations.containsKey(name)) { for (Class configuration : this.configurations.get(name) .getConfiguration()) { context.register(configuration); } } for (Map.Entry entry : this.configurations.entrySet()) { if (entry.getKey().startsWith("default.")) { for (Class configuration : entry.getValue().getConfiguration()) { context.register(configuration); } } } context.register(PropertyPlaceholderAutoConfiguration.class, this.defaultConfigType); context.getEnvironment().getPropertySources().addFirst(new MapPropertySource( this.propertySourceName, Collections.singletonMap(this.propertyName, name))); if (this.parent != null) { // Uses Environment from parent as well as beans context.setParent(this.parent); // jdk11 issue // https://github.com/spring-cloud/spring-cloud-netflix/issues/3101 context.setClassLoader(this.parent.getClassLoader()); } context.setDisplayName(generateDisplayName(name)); context.refresh(); return context;}看完上述内容，你们对Feign中FeignClientFactoryBean的作用是什么有进一步的了解吗？如果还想了解更多知识或者相关内容，请关注行业资讯频道，感谢大家的支持。

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