Feign動態設置header和原理

項目中用到了Feign作遠程調用, 有部分場景須要動態配置header

開始的作法是經過 @RequestHeader 設置參數來實現動態的header配置

例如:

@GetMapping(value = "/test", consumes = {MediaType.APPLICATION_JSON_UTF8_VALUE})    
String access(@RequestHeader("Auth") String auth, @RequestBody Expression expression);

這種方式雖然能夠達到header的動態配置, 可是當參數過多時會下降接口可用性, 因此想經過傳遞bean的方式來設置header

先說解決辦法:

public class HeaderInterceptor implements RequestInterceptor {



    @Override
    public void apply(RequestTemplate requestTemplate) {
        byte[] bytes = requestTemplate.requestBody().asBytes();
        Identity identity = JSONObject.parseObject(bytes, Identity.class);
        requestTemplate.header("Auth", identity.getSecret());
    }
} 
/**
 * configuration指定Interceptor
**/
@FeignClient(name = "test", url = "127.0.0.1:8300", configuration = HeaderInterceptor.class)
public interface GolangTestHandle2 {

    @GetMapping(value = "/handler", consumes = {MediaType.APPLICATION_JSON_UTF8_VALUE})
    String handle(Identity identity);

}

自定義Interceptor實現RequestInterceptor接口, 回調方法apply提供了RequestTemplate對象, 對象內部封裝了request的全部信息, 最後經過configuration指定接口, 以後就隨便你怎麼玩了(例如經過body獲取接口參數並動態設置header)

值得注意的一點是HeaderInterceptor若是注入到Springboot容器的話會全局生效, 就是說及時沒有指定configuration也會對全局feign接口生效, 爲何呢? 這裏簡單說明一下

首先Feign爲每一個feign class建立springcontext上下文
spring經過調用getObject獲取feign工廠實例

@Override
    public Object getObject() throws Exception {
        return getTarget();
    }

內部調用FeignClientFatoryBean.getTarget()方法

<T> T getTarget() {
        //獲取feign上下文
        FeignContext context = this.applicationContext.getBean(FeignContext.class);
        //構建feign Builder
        Feign.Builder builder = feign(context);
        ...
    }

根據feign(FeignContext context)構建Builder

protected Feign.Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(this.type);

        // @formatter:off
        Feign.Builder builder = get(context, Feign.Builder.class)
                // required values
                .logger(logger)
                //默認springEncoder
                .encoder(get(context, Encoder.class))
                //默認OptionalDecoder
                .decoder(get(context, Decoder.class))
                //默認SpringMvcContrat
                .contract(get(context, Contract.class));
        // @formatter:on
        //配置該feign的context
        configureFeign(context, builder);

        return builder;
    }

在構建過程當中經過FeignClientFactoryBean.configureUsingConfiguration爲feign class註冊基本的配置項, 其中也包括了Interceptor的註冊

protected void configureUsingConfiguration(FeignContext context,
            Feign.Builder builder) {
        Logger.Level level = getOptional(context, Logger.Level.class);
        if (level != null) {
            builder.logLevel(level);
        }
        Retryer retryer = getOptional(context, Retryer.class);
        if (retryer != null) {
            builder.retryer(retryer);
        }
        ErrorDecoder errorDecoder = getOptional(context, ErrorDecoder.class);
        if (errorDecoder != null) {
            builder.errorDecoder(errorDecoder);
        }
        Request.Options options = getOptional(context, Request.Options.class);
        if (options != null) {
            builder.options(options);
        }
        //從feign context獲取interceptors
        Map<String, RequestInterceptor> requestInterceptors = context
                .getInstances(this.contextId, RequestInterceptor.class);
        if (requestInterceptors != null) {
            builder.requestInterceptors(requestInterceptors.values());
        }

        if (this.decode404) {
            builder.decode404();
        }
    }

contextId爲具體的feign class id, RequestInterceptor爲具體的接口, 便是說經過context.getInstances獲取全部RequestInterceptor實例並註冊到builder中.

public <T> Map<String, T> getInstances(String name, Class<T> type) {
        AnnotationConfigApplicationContext context = getContext(name);
        //使用beanNamesForTypeIncludingAncestors
        if (BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context,
                type).length > 0) {
            return BeanFactoryUtils.beansOfTypeIncludingAncestors(context, type);
        }
        return null;
    }

獲取工廠中的實例使用的是beanNamesForTypeIncludingAncestors方法, 該不只會總feign的factory中查找, 也會經過父級別spring工廠查找相應實例(相似於springmvc的工廠)

也是由於該方法, 及時你沒有在FeignClient中配置configuration, 可是你的Interceptor經過@Component等方法注入容器的話也會全局生效的, 因此若是指向讓你的Interceptor部分生效不讓它注入到Spring容器就好