Servlet responses to upload/download requests

Question

My task is to write a program to store files in object store. One of the subtasks requires to send json or xml format response to the file uploader/downloader as requested by client.

The following rules must be followed:

                         entry                         
               +-------------------------+             
               v                         v             
           upload                      download        
       +-----------+              +--------------+     
       v           v              v              v     
    succ          err            succ           err    
  +-----+       +-----+                       +-----+  
  v     v       v     v                       v     v  
json1  xml1    json2  xml2                  josn2  xml2

1. if user uploads file with success, return json/xml type 1
2. if user uploads file with error, return json/xml type 2
3. if user downloads file with success, don't change return object
4. if user downloads file with error, return json/xml type 2

I've managed to solve the task but I'm not satisfied with the class dependencies and nested if/else-s I have. I think mixture of abstract factory and strategy are suitable for the issue. Can you give me a hint on how I can deal with the problem?

My code snippet:

public Result upload(HttpServletRequest request) {
        UploadRequestParams uploadParams = UploadRequestParams.getObjectFrom(request);
        ... // create info object
        Result res = handleUploadRequest(uploadParams);

        Result result = jsonXml(info, res);
        return result;
    }

private Result jsonXml(RequestInfo info, Result result) {
        Serializer ser;
        if ("xml".equals(format)) {
            ser = new XmlSerializer();
        } else {
            ser = new JsonSerializer();
        }
        Result res = ser.serialize(info, result);

        return res;
    }

@Override
public Result serialize(RequestInfo info, Result result) { // json implementation
        GsonBuilder builder = new GsonBuilder();
        Gson g = builder.create();

        InputStream stream = null;
        InfoInterface wrap; 
        if (info.isUpload()) {
            if (result.isValid()) {
                wrap = new InfoWrapperImpl1(info, result);
            } else {
                wrap = new InfoWrapperImpl2(info, result);
            }
        } else {
            wrap = new InfoWrapperImpl1(info, result);
        }
        String res = g.toJson(wrap);
        stream = new ByteArrayInputStream(res.getBytes(StandardCharsets.UTF_8));
        Result newRes = Result.getBuilder().setInputStream(stream).setResultCode(result.getResultCode()).build();
        return newRes;
    }

private class InfoWrapperImpl1 implements InfoInterface {
        private String fileName;
        private ResultCode code;

        public InfoWrapper1(RequestInfo info, Result res) {
            this.fileName = info.getUniqueName();
            this.code = res.getCode;
        }
    }

UML class diagram:

EDIT

I rewrote serialize method, but looks like to be bound to the parameters' implementation. Am I right? On the other, I got rid of the ugly nested classes.

@Override
    public Result serialize(RequestInfo info, Result result) {

        JsonObject body = new JsonObject();

        JsonObject resultCode = new JsonObject();
        resultCode.addProperty("code", result.getResultCode().getCode());
        resultCode.addProperty("value", result.getResultCode().getDescription());

        if (info.isUploadRequest() && result.isValid()) {
            body.addProperty(fileTag, info.getExtendedName());
            body.addProperty("checksum", result.getMySwiftObject().getEtag());
        }
        body.add(statusTag, resultCode);

        String jsonRes = body.toString();
        InputStream stream = new ByteArrayInputStream(jsonRes.getBytes(StandardCharsets.UTF_8));
        return Result.getBuilder().setInputStream(stream).setResultCode(result.getResultCode()).build();
    }

Answer 1

   if (info.isUpload()) {
        if (result.isValid()) {
            wrap = new InfoWrapperImpl1(info, result);
        } else {
            wrap = new InfoWrapperImpl2(info, result);
        }
    } else {
        wrap = new InfoWrapperImpl1(info, result);
    }

Can be written as:

   if (!info.isUpload() || result.isValid()) {
        wrap = new InfoWrapperImpl1(info, result);
    } else {
        wrap = new InfoWrapperImpl2(info, result);
    }

Also InfoWrapperImpl1 and InfoWrapperImpl2 are not very good names, as they are not expressive and look quite similar to each other.