How to Download a File from a Spring Boot REST Service: Why InputStreamReader Fails and How to Fix It with InputStreamResource or ByteArrayResource?

Downloading a File from Spring Boot REST Service

This article addresses the issue of downloading a file from a Spring Boot REST service effectively. The code provided below attempts to facilitate this functionality:

<code class="java">@RequestMapping(path="/downloadFile",method=RequestMethod.GET)
@Consumes(MediaType.APPLICATION_JSON_VALUE)
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));
        System.out.println("The length of the file is : "+file2Upload.length());

        return ResponseEntity.ok().headers(headers).contentLength(file2Upload.length())
                .contentType(MediaType.parseMediaType("application/octet-stream"))
                .body(i);
        }</code>

However, upon attempting to download the file through a browser, the process initiates but ultimately fails. The following options can be explored to address this issue:

Option 1: Utilizing an InputStreamResource

An InputStreamResource can be employed to represent an InputStream. It should be considered when other specific Resource implementations are not applicable.

<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: Using a ByteArrayResource

As recommended by the documentation for InputStreamResource, a ByteArrayResource can also be employed.

<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>

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