How to download file in Android using Retrofit library?

Question

I need to download all types of file (binary, image, text, etc) using Retrofit library in my app. All the examples on the net is using HTML GET method. I need to use POST to prevent automatic caching.

My question is how to download a file using POST method in Retrofit?

Answer 1

In kotlin, Do this:

In your service add method:

    @Streaming
    @GET
    suspend fun downloadFile(@Url fileUrl:String): Response<ResponseBody>

To call this method, from ViewModel:

viewModelScope.launch {
     val responseBody=yourServiceInstance.downloadFile(url).body()
     saveFile(responseBody,pathWhereYouWantToSaveFile)
}

To save file:

fun saveFile(body: ResponseBody?, pathWhereYouWantToSaveFile: String):String{
        if (body==null)
            return ""
        var input: InputStream? = null
        try {
            input = body.byteStream()
            //val file = File(getCacheDir(), "cacheFileAppeal.srl")
            val fos = FileOutputStream(pathWhereYouWantToSaveFile)
            fos.use { output ->
                val buffer = ByteArray(4 * 1024) // or other buffer size
                var read: Int
                while (input.read(buffer).also { read = it } != -1) {
                    output.write(buffer, 0, read)
                }
                output.flush()
            }
            return pathWhereYouWantToSaveFile
        }catch (e:Exception){
            Log.e("saveFile",e.toString())
        }
        finally {
            input?.close()
        }
        return ""
    }

Note:

1. Make sure your refrofit client's base url and the url passed to downloadFile makes valid file url:

Retrofit's Base url + downloadFile's method url = File url

2. Here I am using suspend keyword before downloadFile to call this from ViewModel, I have used viewModelScope.launch {} you can use different coroutine scope according to your caller end.

3. Now pathWhereYouWantToSaveFile, If you want to store file into project's file directory, you can do this:

val fileName=url.substring(url.lastIndexOf("/")+1)
val pathWhereYouWantToSaveFile = myApplication.filesDir.absolutePath+fileName

4. If you are storing the downloaded file under file or cache directory, you don't need to acquire permission, otherwise for public storage, you know the process.

Answer 2

Use @Streaming

Asynchronous

EDIT 1

//On your api interface
@POST("path/to/your/resource")
@Streaming
void apiRequest(Callback<POJO> callback);

restAdapter.apiRequest(new Callback<POJO>() {
        @Override
        public void success(POJO pojo, Response response) {
            try {
                //you can now get your file in the InputStream
                InputStream is = response.getBody().in();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void failure(RetrofitError error) {

        }
    });

Synchronous

//On your api interface
@POST("path/to/your/resource")
@Streaming
Response apiRequest();

Response response = restAdapter.apiRequest();

try {
    //you can now get your file in the InputStream
    InputStream is = response.getBody().in();
} catch (IOException e) {
    e.printStackTrace();
}

Answer 3

This is How to DOWNLOAD file in Retrofit 2

public interface ServerAPI {
        @GET
        Call<ResponseBody> downlload(@Url String fileUrl);

        Retrofit retrofit =
                new Retrofit.Builder()
                        .baseUrl("http://192.168.43.135/retro/") // REMEMBER TO END with /
                        .addConverterFactory(GsonConverterFactory.create())
                 .build();

}

    //How To Call
public void download(){
        ServerAPI api = ServerAPI.retrofit.create(ServerAPI.class);
        api.downlload("http://192.168.43.135/retro/pic.jpg").enqueue(new Callback<ResponseBody>() {
                    @Override
                    public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response) {
                        try {
                            File path = Environment.getExternalStorageDirectory();
                            File file = new File(path, "file_name.jpg");
                            FileOutputStream fileOutputStream = new FileOutputStream(file);
                            IOUtils.write(response.body().bytes(), fileOutputStream);
                        }
                        catch (Exception ex){
                        }
                    }

                    @Override
                    public void onFailure(Call<ResponseBody> call, Throwable t) {
                    }
                });
}