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一、读取注解信息
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入口
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;
@SpringBootApplication
@EnableFeignClients
public 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 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 target(FeignClientFactoryBean factory, Feign.Builder feign,
FeignContext context, Target.HardCodedTarget 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 target(FeignClientFactoryBean factory, Feign.Builder feign,
FeignContext context, Target.HardCodedTarget target) {
return feign.target(target);
}
} 然后再看 feign.target(target);方法
publicT target(Target 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