feign响应Image流对象

feign面向方法签名的http调用，越来越受欢迎，类型于rpc的thrift，只需要关注方法签名和返回值即可，当然feign响应流对象时，需要我们做一下特殊处理，否则会出现异常。也有一些文章通过重写httpmessageconvert来实现，但我测试后发现还是失败的。
> accept: image/*会返回406 not acceptable

### 解决方法
feign代码，注意返回值必须是`feign.response`
```
  @postmapping(value = "/wxa/getwxacodeunlimit")
  feign.response getqrimagepath(@requestparam("access_token") string accesstoken,@requestbody map<string, object> body);

  class weixinclientfallback implements weixinclient {
```
restcontroller代码,需要显示声明`produces`类型，这里因为是图片，所以声明为`mediatype.image_jpeg_value`
```
 @getmapping(value = "/v1/api/sales/qrcode", produces = mediatype.image_jpeg_value)
  public void qrcode(httpservletresponse response) {
    //获取token
    map<string, object> tokenmap = weixinclient.gettoken("client_credential", wxappid, wxappsecret);
    if (tokenmap == null) {
      throw exceptions.paramerror("获取token失败");
    }
    if (tokenmap.containskey("errcode")) {
      throw exceptions.paramerror(maputils.getstring(tokenmap, "errmsg"));
    }
    string scene = string.format("salespersonid=%s&agencyid=%s",
        tokencontext.gettoken().getuserid(),
        tokencontext.gettoken().getcompanyid());
    string token = maputils.getstring(tokenmap, "access_token");
    map<string, object> requestparams = new hashmap<>();
    requestparams.put("scene", scene);
    requestparams.put("page", weixinpage);
    feign.response imgreponse = weixinclient.getqrimagepath(token, requestparams);
    if (imgreponse == null) {
      throw exceptions.paramerror("获取二维码失败");
    }
    try (inputstream inputstream = imgreponse.body().asinputstream();
         servletoutputstream outputstream = response.getoutputstream()) {
      response.setcontenttype("image/png");
      outputstream.write(ioutils.tobytearray(inputstream));
    } catch (runtimeexception e) {
      throw exceptions.paramerror("获取二维码失败");
    } catch (exception ex) {
      throw exceptions.paramerror("获取二维码失败");
    }
  }
```