Trouble Implementing Asynchronous File Download in Spring Boot with CompletableFuture
I'm trying to debug I'm working through a tutorial and I'm integrating two systems and I've searched everywhere and can't find a clear answer. I'm working on a personal project and I'm trying to implement an asynchronous file download feature in my Spring Boot application using `CompletableFuture`. The goal is to allow users to download files without blocking the main thread while keeping the UI responsive. Despite following the documentation, I'm running into a `java.lang.IllegalStateException: No WebApplicationContext found` error when I attempt to start the download. Here’s the code snippet I’m using: ```java @Service public class FileService { public CompletableFuture<Resource> downloadFile(String filePath) { return CompletableFuture.supplyAsync(() -> { File file = new File(filePath); if (!file.exists()) { throw new FileNotFoundException("File not found: " + filePath); } return new UrlResource(file.toURI()); }); } } ``` I have a controller that invokes this service: ```java @RestController @RequestMapping("/api/files") public class FileController { @Autowired private FileService fileService; @GetMapping("/download") public ResponseEntity<Resource> download(@RequestParam String filePath) { CompletableFuture<Resource> resourceFuture = fileService.downloadFile(filePath); // Wait for the result Resource resource = resourceFuture.join(); return ResponseEntity.ok() .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + resource.getFilename()) .body(resource); } } ``` I have also annotated my main application class with `@EnableAsync` but still face the same exception. I've searched for solutions online and ensured that my Spring Boot version is 2.5.4 which should support these features. Any idea what might be causing this error? I would appreciate any tips for correctly implementing this asynchronous file download while maintaining a responsive application. This is part of a larger service I'm building. I'd really appreciate any guidance on this. I'm working in a Linux environment. What's the best practice here? This is for a REST API running on Ubuntu 20.04.