How to Successfully Download Files from a Spring Boot REST Service?

Downloading Files from a Spring Boot REST Service

In Spring Boot, you can utilize a REST service to download files. However, a common issue arises when downloading fails.

Here's a service implementation that encounters this error:

<code class="java">@RequestMapping(path="/downloadFile",method=RequestMethod.GET)
public  ResponseEntity<InputStreamReader> downloadDocument(
                String acquistionId,
                String fileType,
                Integer expressVfId) throws IOException {
    // Code for file acquisition...

    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>

To resolve this issue, consider the following solutions:

Option 1: Using an InputStreamResource

Use an InputStreamResource to wrap the InputStream of the file:

<code class="java">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 suggested by the InputStreamResource documentation, using a ByteArrayResource may be more efficient:

<code class="java">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 incorporating these solutions, you should be able to download files successfully from your Spring Boot REST service.

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