Spring Cloud 声明式REST客户端 OpenFeign -- 5. Feign Hystrix fallback 后备方案

Hystrix支持后备方案(fallback)的概念: 电路断开(也就是不通电时)或者遇到错误时执行一段缺省代码。要对一个给定的@FeignClient启用后备方案，将它的fallback属性设置成后备方案逻辑实现类的类名。如下所示 ：

@FeignClient(name = "hello", fallback = HystrixClientFallback.class)
protected interface HystrixClient {
    @RequestMapping(method = RequestMethod.GET, value = "/hello")
    Hello iFailSometimes();
}

static class HystrixClientFallback implements HystrixClient {
    @Override
    public Hello iFailSometimes() {
        return new Hello("fallback");
    }
}

如果你需要知道后备方案逻辑被触发的原因，那就得使用@FeignClient的属性fallbackFactory。如下所示 :

@FeignClient(name = "hello", fallbackFactory = HystrixClientFallbackFactory.class)
protected interface HystrixClient {
	@RequestMapping(method = RequestMethod.GET, value = "/hello")
	Hello iFailSometimes();
}

@Component
static class HystrixClientFallbackFactory implements FallbackFactory<HystrixClient> {
	@Override
	public HystrixClient create(Throwable cause) {
		return new HystrixClient() {
			@Override
			public Hello iFailSometimes() {
				return new Hello("fallback; reason was: " + cause.getMessage());
			}
		};
	}
}

注意 : 目前在Feign使用Hystrix后备逻辑机制还有一定的限制: 对于返回com.netflix.hystrix.HystrixCommand和rx.Observable的方法，还不支持后备方案(fallback)。