Использование HttpClient 4 (из Apache)
HttpPost post = new HttpPost(url);
MultipartEntity content = new MultipartEntity(HttpMultipartMode.STRICT);
//To add parameters, use StringBody
content.addPart("param", new StringBody("value"));
content.addPart("param1", new StringBody("value1"));
content.addPart("param2", new StringBody("value2"));
//To add files, use InputStreamBody
content.addPart("source", new InputStreamBody(inputStream, mimeType, fileName)); //OR
content.addPart("source", new InputStreamBody(inputStream, mimeType));
//Finally
post.setEntity(content);
Надеюсь, это поможет.