Once you receive the ResponseBody , you need to write its byteStream() to a file. In modern Android development, using Kotlin Coroutines on Dispatchers.IO is the standard way to ensure these disk operations don't block the UI thread.
This guide covers how to download files using Retrofit while maintaining performance and providing a smooth user experience. 1. Define the Retrofit Interface download file with retrofit
To download a file, your API interface must return a ResponseBody . This prevents Retrofit from attempting to parse the binary data into a POJO. Once you receive the ResponseBody , you need
If you are saving to public folders like Downloads , ensure you handle the necessary permissions or use the Storage Access Framework for modern Android versions. If you are saving to public folders like
Always wrap your download logic in a try-catch block to handle network interruptions or disk-full scenarios.
For large files, you use the @Streaming annotation. This tells Retrofit to pass the raw bytes immediately to you rather than buffering the whole file in RAM.
interface FileDownloadService { // Option 1: Fixed URL @Streaming @GET("path/to/resource.zip") suspend fun downloadFileWithFixedUrl(): ResponseBody // Option 2: Dynamic URL @Streaming @GET suspend fun downloadFileWithDynamicUrl(@Url fileUrl: String): ResponseBody } Use code with caution. 2. Stream and Save the File to Disk