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Feign源码分析之FeignClientFactoryBean

     springcloud-openfeign-core-2.1.1.release.

    继上篇Feign源码分析之EnableFeignClients后,Springcloud中将FeignClient注解的接口封装到FeignClientFactoryBean中,现在来看看FeignClientFactoryBean的实现。

                 

                                                                                         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<Object>, InitializingBean, ApplicationContextAware {
/***********************************
 * WARNING! Nothing in this class should be @Autowired. It causes NPEs because of some
 * lifecycle race condition.
 ***********************************/

private Class&lt;?&gt; type;

private String name;

private String url;

private String contextId;

private String path;

private boolean decode404;

private ApplicationContext applicationContext;

private Class&lt;?&gt; fallback = void.class;

private Class&lt;?&gt; 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

@Override
public Object getObject() throws Exception {
    return getTarget();
}

<T> T getTarget() { FeignContext context = this.applicationContext.getBean(FeignContext.class); Feign.Builder builder = feign(context); ...

    List-3

public class FeignAutoConfiguration {
	@Autowired(required = false)
	private List<FeignClientSpecification> 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<String, RequestInterceptor> 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<C> configurations) {
    for (C client : configurations) {
        this.configurations.put(client.getName(), client);
    }
}

    List-6中

  1. getConext方法获取ApplicationContext,之后从该ApplicationContext中获取bean
  2. getConext方法中,如过name对应的ApplicationContext不存在,则调用createContext方法进行创建
  3. 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> T getInstance(String name, Class<T> 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<String, C> 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.<String, Object>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; }

 

Reference

  1. 源码,github地址略

本文由【克虏伯】发布于开源中国,原文链接:https://my.oschina.net/u/2518341/blog/3113900

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