spring cloud openfeign 源码

一、读取注解信息

　入口

 1 import org.springframework.boot.SpringApplication;
 2 import org.springframework.boot.autoconfigure.SpringBootApplication;
 3 import org.springframework.cloud.openfeign.EnableFeignClients;
 4
 5
 6 @SpringBootApplication
 7 @EnableFeignClients
 8 public class CjsPriceServiceApplication {
 9
10     public static void main(String[] args) {
11         SpringApplication.run(CjsPriceServiceApplication.class, args);
12     }
13
14 }

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

1 @Retention(RetentionPolicy.RUNTIME)
2 @Target(ElementType.TYPE)
3 @Documented
4 @Import(FeignClientsRegistrar.class)
5 public @interface EnableFeignClients {
6 。。。。
7 }

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

1     @Override
2     public void registerBeanDefinitions(AnnotationMetadata metadata,
3             BeanDefinitionRegistry registry) {
4         registerDefaultConfiguration(metadata, registry);
5         registerFeignClients(metadata, registry);
6     }

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

1     @Override
2     public Object getObject() throws Exception {
3         return getTarget();
4     }

 1 <T> T getTarget() {
 2         FeignContext context = this.applicationContext.getBean(FeignContext.class);
 3         Feign.Builder builder = feign(context);
 4
 5         if (!StringUtils.hasText(this.url)) {
 6             if (!this.name.startsWith("http")) {
 7                 this.url = "http://" + this.name;
 8             }
 9             else {
10                 this.url = this.name;
11             }
12             this.url += cleanPath();
13             return (T) loadBalance(builder, context,
14                     new HardCodedTarget<>(this.type, this.name, this.url));
15         }
16         if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
17             this.url = "http://" + this.url;
18         }
19         String url = this.url + cleanPath();
20         Client client = getOptional(context, Client.class);
21         if (client != null) {
22             if (client instanceof LoadBalancerFeignClient) {
23                 // not load balancing because we have a url,
24                 // but ribbon is on the classpath, so unwrap
25                 client = ((LoadBalancerFeignClient) client).getDelegate();
26             }
27             builder.client(client);
28         }
29         Targeter targeter = get(context, Targeter.class);
30         return (T) targeter.target(this, builder, context,
31                 new HardCodedTarget<>(this.type, this.name, url));
32     }

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

 1 package org.springframework.cloud.openfeign;
 2
 3 import feign.Feign;
 4 import feign.Target;
 5
 6 /**
 7  * @author Spencer Gibb
 8  */
 9 interface Targeter {
10
11     <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
12             FeignContext context, Target.HardCodedTarget<T> target);
13
14 }

默认实现类

 1 package org.springframework.cloud.openfeign;
 2
 3 import feign.Feign;
 4 import feign.Target;
 5
 6 /**
 7  * @author Spencer Gibb
 8  */
 9 class DefaultTargeter implements Targeter {
10
11     @Override
12     public <T> T target(FeignClientFactoryBean factory, Feign.Builder feign,
13             FeignContext context, Target.HardCodedTarget<T> target) {
14         return feign.target(target);
15     }
16
17 }

然后再看 feign.target(target);方法

 1     public <T> T target(Target<T> target) {
 2       return build().newInstance(target);
 3     }
 4
 5     public Feign build() {
 6       SynchronousMethodHandler.Factory synchronousMethodHandlerFactory =
 7           new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger,
 8               logLevel, decode404, closeAfterDecode, propagationPolicy);
 9       ParseHandlersByName handlersByName =
10           new ParseHandlersByName(contract, options, encoder, decoder, queryMapEncoder,
11               errorDecoder, synchronousMethodHandlerFactory);
12       return new ReflectiveFeign(handlersByName, invocationHandlerFactory, queryMapEncoder);
13     }
14   }

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

 1   public <T> T newInstance(Target<T> target) {
 2     Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
 3     Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
 4     List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();
 5
 6     for (Method method : target.type().getMethods()) {
 7       if (method.getDeclaringClass() == Object.class) {
 8         continue;
 9       } else if (Util.isDefault(method)) {
10         DefaultMethodHandler handler = new DefaultMethodHandler(method);
11         defaultMethodHandlers.add(handler);
12         methodToHandler.put(method, handler);
13       } else {
14         methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
15       }
16     }
17     InvocationHandler handler = factory.create(target, methodToHandler);
18     T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
19         new Class<?>[] {target.type()}, handler);
20
21     for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
22       defaultMethodHandler.bindTo(proxy);
23     }
24     return proxy;
25   }

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

原文地址：https://www.cnblogs.com/yechen2019/p/11676859.html