一、读取注解信息

入口

import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.cloud.openfeign.EnableFeignClients;@SpringBootApplication@EnableFeignClientspublic class CjsPriceServiceApplication { public static void main(String[] args) { SpringApplication.run(CjsPriceServiceApplication.class, args); }}

spring boot 项目启动后会自动扫描application上面的注解，@EnableFeignClients的注解如下

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

在注解中导入了 FeignClientsRegistrar类，用来像spring注册，EnableFeignClients和FeignClient上面开发人员添加的注解信息

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

二、当项目启动，读取@Autowired时会调用，实现了FactoryBean接口的FeignClientFactoryBean.getObject()方法

@Override public Object getObject() throws Exception { return getTarget(); }
<T> T getTarget() { FeignContext context = this.applicationContext.getBean(FeignContext.class); Feign.Builder builder = feign(context); if (!StringUtils.hasText(this.url)) { if (!this.name.startsWith("http")) { this.url = "http://" + this.name; } else { this.url = this.name; } this.url += cleanPath(); return (T) loadBalance(builder, context, new HardCodedTarget<>(this.type, this.name, this.url)); } if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) { this.url = "http://" + this.url; } String url = this.url + cleanPath(); Client client = getOptional(context, Client.class); if (client != null) { if (client instanceof LoadBalancerFeignClient) { // not load balancing because we have a url, // but ribbon is on the classpath, so unwrap client = ((LoadBalancerFeignClient) client).getDelegate(); } builder.client(client); } Targeter targeter = get(context, Targeter.class); return (T) targeter.target(this, builder, context, new HardCodedTarget<>(this.type, this.name, url)); }

可以看到 getTarget（）有两种返回结果的情况，其原理都一样后来调用了 targeter.target（）方法

package org.springframework.cloud.openfeign;import feign.Feign;import feign.Target;/** * @author Spencer Gibb */interface Targeter { <T> T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context, Target.HardCodedTarget<T> target);}

默认实现类

package org.springframework.cloud.openfeign;import feign.Feign;import feign.Target;/** * @author Spencer Gibb */class DefaultTargeter implements Targeter { @Override public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context, Target.HardCodedTarget<T> target) { return feign.target(target); }}

然后再看 feign.target(target);方法

public <T> T target(Target<T> target) { return build().newInstance(target); } public Feign build() { SynchronousMethodHandler.Factory synchronousMethodHandlerFactory = new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger, logLevel, decode404, closeAfterDecode, propagationPolicy); ParseHandlersByName handlersByName = new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder, errorDecoder, synchronousMethodHandlerFactory); return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder); } }

build（）方法返回了创建代理类的对象，然后调用了创建代理的 newInstance方法

public <T> T newInstance(Target<T> target) { Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target); Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>(); List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>(); for (Method method : target.type().getMethods()) { if (method.getDeclaringClass() == Object.class) { continue; } else if (Util.isDefault(method)) { DefaultMethodHandler handler = new DefaultMethodHandler(method); defaultMethodHandlers.add(handler); methodToHandler.put(method, handler); } else { methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method))); } } InvocationHandler handler = factory.create(target, methodToHandler); T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class<?>[] {target.type()}, handler); for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) { defaultMethodHandler.bindTo(proxy); } return proxy; }

最后，当我们项目中使用 @Autowired注入时，就回调用工厂类 FeignClientFactoryBean方法的 getObject()方法 返回我们的代理对象

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。