Why is my Spring Boot REST service download failing, despite the browser initiating the process?

Download a File from Spring Boot Rest Service: Troubleshooting Failed Downloads

This article addresses a problem encountered when attempting to download a file via a Spring Boot REST service. Despite initiation of the download in the browser, the process consistently fails. Here's an analysis of the issue and potential solutions:

The Service Method:

The provided code demonstrates the service method responsible for downloading the file:

<code class="java">@RequestMapping(path="/downloadFile",method=RequestMethod.GET)
public ResponseEntity<InputStreamReader> downloadDocument(String acquistionId, String fileType, Integer expressVfId) throws IOException {
    File file2Upload = new File("C:\Users\admin\Desktop\bkp\1.rtf");
    HttpHeaders headers = new HttpHeaders();
    headers.add("Cache-Control", "no-cache, no-store, must-revalidate");
    headers.add("Pragma", "no-cache");
    headers.add("Expires", "0");
    InputStreamReader i = new InputStreamReader(new FileInputStream(file2Upload));
    return ResponseEntity.ok().headers(headers).contentLength(file2Upload.length())
            .contentType(MediaType.parseMediaType("application/octet-stream"))
            .body(i);
}</code>

Option 1: Utilizing an InputStreamResource

The provided code creates an InputStreamReader from a file and returns it with a ResponseEntity. However, it's recommended to use an InputStreamResource from the spring-core library. This implementation offers a resource for streams, ensuring proper handling of the stream during the download process.

<code class="java">@RequestMapping(path = "/download", method = RequestMethod.GET)
public ResponseEntity<Resource> download(String param) throws IOException {
    InputStreamResource resource = new InputStreamResource(new FileInputStream(file));
    return ResponseEntity.ok()
            .headers(headers)
            .contentLength(file.length())
            .contentType(MediaType.APPLICATION_OCTET_STREAM)
            .body(resource);
}</code>

Option 2: Employing a ByteArrayResource

The Spring documentation suggests utilizing a ByteArrayResource instead of an InputStreamResource. Using this resource type involves reading the entire file into a byte array and creating a resource from it. This approach can be advantageous in certain scenarios, such as improved performance for small files.

<code class="java">@RequestMapping(path = "/download", method = RequestMethod.GET)
public ResponseEntity<Resource> download(String param) throws IOException {
    Path path = Paths.get(file.getAbsolutePath());
    ByteArrayResource resource = new ByteArrayResource(Files.readAllBytes(path));
    return ResponseEntity.ok()
            .headers(headers)
            .contentLength(file.length())
            .contentType(MediaType.APPLICATION_OCTET_STREAM)
            .body(resource);
}</code>

By implementing either of these options, the issue with download failures should be resolved, enabling seamless file downloads through the Spring Boot REST service.

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