Feign动态设置header和原理

项目中用到了Feign作远程调用, 有部分场景须要动态配置header

开始的作法是经过 @RequestHeader 设置参数来实现动态的header配置

例如:

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

这种方式虽然能够达到header的动态配置, 可是当参数过多时会下降接口可用性, 因此想经过传递bean的方式来设置header

先说解决办法:

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);

}

自定义Interceptor实现RequestInterceptor接口, 回调方法apply提供了RequestTemplate对象, 对象内部封装了request的全部信息, 最后经过configuration指定接口, 以后就随便你怎么玩了(例如经过body获取接口参数并动态设置header)

值得注意的一点是HeaderInterceptor若是注入到Springboot容器的话会全局生效, 就是说及时没有指定configuration也会对全局feign接口生效, 为何呢? 这里简单说明一下

首先Feign为每一个feign class建立springcontext上下文
spring经过调用getObject获取feign工厂实例

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

内部调用FeignClientFatoryBean.getTarget()方法

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

根据feign(FeignContext context)构建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)
                //默认springEncoder
                .encoder(get(context, Encoder.class))
                //默认OptionalDecoder
                .decoder(get(context, Decoder.class))
                //默认SpringMvcContrat
                .contract(get(context, Contract.class));
        // @formatter:on
        //配置该feign的context
        configureFeign(context, builder);

        return builder;
    }

在构建过程当中经过FeignClientFactoryBean.configureUsingConfiguration为feign class注册基本的配置项, 其中也包括了Interceptor的注册

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);
        }
        //从feign context获取interceptors
        Map<String, RequestInterceptor> requestInterceptors = context
                .getInstances(this.contextId, RequestInterceptor.class);
        if (requestInterceptors != null) {
            builder.requestInterceptors(requestInterceptors.values());
        }

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

contextId为具体的feign class id, RequestInterceptor为具体的接口, 便是说经过context.getInstances获取全部RequestInterceptor实例并注册到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;
    }

获取工厂中的实例使用的是beanNamesForTypeIncludingAncestors方法, 该不只会总feign的factory中查找, 也会经过父级别spring工厂查找相应实例(相似于springmvc的工厂)

也是由于该方法, 及时你没有在FeignClient中配置configuration, 可是你的Interceptor经过@Component等方法注入容器的话也会全局生效的, 因此若是指向让你的Interceptor部分生效不让它注入到Spring容器就好