gistfile1.java

        RequestBuilder requestBuilder = new RequestBuilder("POST").setUrl("http://myUrl/multipartUploadEndpoint");

        MultipartBodyGeneratorFeeder bodyFeeder = MultipartBodyGeneratorFeeder.create(requestBuilder);

        Request request = requestBuilder.build();

        ListenableFuture<Response> asyncRes = asyncHttpClient
                .prepareRequest(request)
                .execute(new AsyncCompletionHandlerBase());

        bodyFeeder.addBodyPart(new StringPart("param1", "x"))
                .addBodyPart(new StringPart("param2", "y"))
                .addBodyPart(new StringPart("param3", "z"))
                .addBodyPart(new FilePart("file", inputStream))
                .feed();

        Response uploadResponse = asyncRes.get();