通过Feign在服务之间传递header请求头信息

微服务等情况下，通过feign调用接口，很多情况下需要在fegin所在的服务中心获取header等等的信息，默认情况下是不带有的。

所以，最好是自行处理，转发所有，以下以header为例

@Slf4j
public class FeignConfig implements RequestInterceptor {

    @Override
    public void apply(RequestTemplate requestTemplate) {
        ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        if(null == attributes){
            log.info("attributes在feginConfig中没有获取到");
            attributes = new ServletRequestAttributes((HttpServletRequest) new MockHttpServletRequest());
            RequestContextHolder.setRequestAttributes(attributes);
        }
        HttpServletRequest request = attributes.getRequest();
        log.info("RequestTemplate.headers:" + JSON.toJSONString(requestTemplate.headers()));
        if (null != httpServletRequest) {
            Map<String, String> headers = getHeaders(httpServletRequest);
            for (Map.Entry<String, String> entry : headers.entrySet()) {
                requestTemplate.header(entry.getKey(), entry.getValue());
            }
        }
    }

    private HttpServletRequest getHttpServletRequest() {
        try {
            return ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

    private Map<String, String> getHeaders(HttpServletRequest request) {
        Map<String, String> map = new LinkedHashMap<>();
        Enumeration<String> enumeration = request.getHeaderNames();
        if (enumeration != null) {
            while (enumeration.hasMoreElements()) {
                String key = enumeration.nextElement();
                String value = request.getHeader(key);
                map.put(key, value);
            }
        }
        return map;
    }
}