SpringCloud @FeignClient 参数详解

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本文围绕Spring Cloud的@FeignClient注解展开，作者因工作中遇到FeignClient的bug而进行总结。介绍了@FeignClient源码中的常用方法，如url是访问地址。还详细讲解了fallback与fallbackFactory，包括使用方式、优先级，以及二者的区别。

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SpringCloud @FeignClient 参数详解

今天因为工作中遇到FeignClient一个奇葩的bug,后面仔细研究了,找出了原因,那么刚好对FeignClient 这个注解总结一下:

1、先看@FeignClient 源码: 源码如下,本文最后面.

11个方法,常用方法说明如下

@FeignClient(name = "service-name", url = "${feign.urls.service-name:}", fallback =ApiFallBack.class,configuration = Interceptor.class)

1.value,name 这两个就同一个意思:对应的是调用的微服务的服务名,对用服务发现、走网关调用,这个很关键.

2.url:这是访问地址,可以直接提供给外部调用,也可以直接写如192.168.1.11:8800/applicationName

3.fallback 与 fallbackFactory

就给@FeignClient注解设置fallback属性，并且回退类要继承@FeignClient所注解的接口

ApiFallBack类拿出去单独作为一个类的话，我们就得在该类上添加注解@Component

如果fallback默认优先级比fallfactory优先级高。所以二者都存在的话，会访问fallback的回退方法。
这里不做演示。
那么fallback和fallfactory有什么区别呢

@FeignClient(name = "service-name", fallbackFactory = HystrixClientFallbackFactory.class)

protected interface HystrixClient {

@RequestMapping(method = RequestMethod.GET, value = "/test")

Hello iFailSometimes();

}

@Component

static class HystrixClientFallbackFactory implements FallbackFactory<HystrixClient> {

@Override

public HystrixClient create(Throwable cause) {

return new HystrixClientWithFallBackFactory() {

@Override

public Hello iFailSometimes() {

return new Hello("fallback; reason was: " + cause.getMessage());

}

};

}

fallback和fallfactory区别：

fallback 只是重写了回退方法。

fallfactory 层面比较深，因为它用线程抛出了异常,可以看到底层具体问题。

/**
 * Annotation for interfaces declaring that a REST client with that interface should be
 * created (e.g. for autowiring into another component). If ribbon is available it will be
 * used to load balance the backend requests, and the load balancer can be configured
 * using a <code>@RibbonClient</code> with the same name (i.e. value) as the feign client.
 *
 * @author Spencer Gibb
 * @author Venil Noronha
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface FeignClient {

   /**
    * The name of the service with optional protocol prefix. Synonym for {@link #name()
    * name}. A name must be specified for all clients, whether or not a url is provided.
    * Can be specified as property key, eg: ${propertyKey}.
    */
   @AliasFor("name")
   String value() default "";

   /**
    * The service id with optional protocol prefix. Synonym for {@link #value() value}.
    *
    * @deprecated use {@link #name() name} instead
    */
   @Deprecated
   String serviceId() default "";

   /**
    * The service id with optional protocol prefix. Synonym for {@link #value() value}.
    */
   @AliasFor("value")
   String name() default "";
   
   /**
    * Sets the <code>@Qualifier</code> value for the feign client.
    */
   String qualifier() default "";

   /**
    * An absolute URL or resolvable hostname (the protocol is optional).
    */
   String url() default "";

   /**
    * Whether 404s should be decoded instead of throwing FeignExceptions
    */
   boolean decode404() default false;

   /**
    * A custom <code>@Configuration</code> for the feign client. Can contain override
    * <code>@Bean</code> definition for the pieces that make up the client, for instance
    * {@link feign.codec.Decoder}, {@link feign.codec.Encoder}, {@link feign.Contract}.
    *
    * @see FeignClientsConfiguration for the defaults
    */
   Class<?>[] configuration() default {};

   /**
    * Fallback class for the specified Feign client interface. The fallback class must
    * implement the interface annotated by this annotation and be a valid spring bean.
    */
   Class<?> fallback() default void.class;

   /**
    * Define a fallback factory for the specified Feign client interface. The fallback
    * factory must produce instances of fallback classes that implement the interface
    * annotated by {@link FeignClient}. The fallback factory must be a valid spring
    * bean.
    *
    * @see feign.hystrix.FallbackFactory for details.
    */
   Class<?> fallbackFactory() default void.class;

   /**
    * Path prefix to be used by all method-level mappings. Can be used with or without
    * <code>@RibbonClient</code>.
    */
   String path() default "";

   /**
    * Whether to mark the feign proxy as a primary bean. Defaults to true.
    */
   boolean primary() default true;

}