Java 将文件从GWT上载到另一个域，响应始终为空

我正在将一个文件从GWT上载到另一个域

文件上传良好，但我从服务器发送的响应在客户端总是达到“null”

                    response.setContentType("text/html");
                    response.setHeader("Access-Control-Allow-Origin", "*");
                    response.getWriter().print("TEST");

仅当我将文件上载到其他域时，响应才为空。。。（在同一个域上，一切正常）

我在GWT文档中也看到了这一点

 Tip:
 The result html can be null as a result of submitting a form to a different domain.

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当我将文件上载到其他域时，是否有任何方法可以在客户端收到回复？有两种可能的答案：

使用生成器

希望能有帮助

    JsonpRequestBuilder requestBuilder = new JsonpRequestBuilder();
    requestBuilder.requestObject(url, new AsyncCallback<FbUser>() {
    @Override
    public void onFailure(Throwable ex) {
        throw SOMETHING_EXCEPTION(ex);
    }

    @Override
    public void onSuccess(ResponseModel resp) {
        if (resp.isError()) {
            // on response error on something
            log.error(resp.getError().getMessage())
            log.error(resp.getError().getCode())
        }
        
        log.info(resp.getAnyData())
    }

public uploadFile() {
    HttpClient httpClient = new DefaultHttpClient();
    HttpContext localContext = new BasicHttpContext();
    HttpPost httpPost = new HttpPost(url);

    FileBody bin = new FileBody(new File(UPLOADED_FILE));
    long size = bin.getContentLength();

    MultipartEntity reqEntity = new MultipartEntity();
    reqEntity.addPart("PART", bin);
    String content = "-";
    try {
         httpPost.setEntity(reqEntity);
            HttpResponse response = httpClient.execute(httpPost, localContext);
            HttpEntity ent = response.getEntity();
            InputStream st = ent.getContent();
            StringWriter writer = new StringWriter();
            IOUtils.copy(st, writer);
            content = writer.toString();                

    } catch (IOException e) {                   
        return "false";
    }
    return content;
}