Use retrofit to download image file

Question

I use Retrofit 1.6.0 on my Android project,

the request url:

https://example.com/image/thumbs/filename/sample.png

My interface like this:

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Answer 1

Of course we usually use Picasso to load image, but sometimes we really need use Retrofit to load a special image (like fetch a captcha image), you need add some header for request, get some value from header of response (of course you can also use Picasso + OkHttp, but in a project you have already use Retrofit to handle most of net requests), so here introduce how to implement by Retrofit 2.0.0 (I have already implemented in my project).

The key point is that you need use okhttp3.ResponseBody to receive response, else Retrofit will parse the response data as JSON, not binary data.

codes:

public interface Api {
    // don't need add 'Content-Type' header, it not works for Retrofit 2.0.0
    // @Headers({"Content-Type: image/png"})
    @GET
    Call fetchCaptcha(@Url String url);
}

Call call = api.fetchCaptcha(url);
call.enqueue(new Callback() {
        @Override
        public void onResponse(Call call, Response response) {
            if (response.isSuccessful()) {
                if (response.body() != null) {
                    // display the image data in a ImageView or save it
                    Bitmap bm = BitmapFactory.decodeStream(response.body().byteStream());
                    ivCaptcha.setImageBitmap(bm);
                } else {
                    // TODO
                }
            } else {
                // TODO
            }
        }

        @Override
        public void onFailure(Call call, Throwable t) {
            // TODO
        }
    });