封装的上传文件

public void upload(String url, Map<String, Object> params, Callback callback) {
    MultipartBody.Builder builder = new MultipartBody.Builder();
    builder.setType(MultipartBody.FORM);
    for (String key : params.keySet()) {
        Object obj = params.get(key);
        if (obj instanceof String) {
            builder.addFormDataPart(key, obj.toString());
        } else if (obj instanceof File) {
            File file = (File) obj;
            builder.addFormDataPart("file", file.getName(), RequestBody.create(MediaType.parse("image/jpeg"), file));
        }
    }
    MultipartBody body = builder.build();

    Request request = new Request.Builder().url(url).post(body).build();
    client.newCall(request).enqueue(callback);
}