Spring REST - 正在下載損壞/空白文件

Question

我正在嘗試創建一個端點來呈現/提供PDF文件。 我已經通過以下鏈接來構建API，但仍面臨一些問題。

鏈接1

鏈接2

以下是我的代碼：

byte[] targetArray = null;

InputStream is = null;

InputStream objectData = object.getObjectContent();

BufferedReader reader = new BufferedReader(new InputStreamReader(objectData));

char[] charArray = new char[8 * 1024];
StringBuilder builder = new StringBuilder();
int numCharsRead;
while ((numCharsRead = reader.read(charArray, 0, charArray.length)) != -1) {

    builder.append(charArray, 0, numCharsRead);
}
reader.close();

objectData.close();
object.close();
targetArray = builder.toString().getBytes();

is = new ByteArrayInputStream(targetArray);


return ResponseEntity.ok().contentLength(targetArray.length).contentType(MediaType.APPLICATION_PDF)
                .cacheControl(CacheControl.noCache()).header("Content-Disposition", "attachment; filename=" + "testing.pdf")
                .body(new InputStreamResource(is));

當我使用郵遞員點擊我的API時，我能夠下載PDF文件，但問題是它完全是空白的。 可能是什么問題？

Answer 1

從服務器下載文件有多種方法 ，可以使用ResponseEntity<InputStreamResource> ， HttpServletResponse .Below是下載的兩種方法。

@GetMapping("/download1")
       public ResponseEntity<InputStreamResource> downloadFile1() throws IOException {

          File file = new File(FILE_PATH);
          InputStreamResource resource = new InputStreamResource(new FileInputStream(file));

          return ResponseEntity.ok()
                .header(HttpHeaders.CONTENT_DISPOSITION,
                      "attachment;filename=" + file.getName())
                .contentType(MediaType.APPLICATION_PDF).contentLength(file.length())
                .body(resource);
       }

要么

您可以使用StreamingResponseBody下載大文件。 在這種情況下，服務器同時將數據寫入OutputStream瀏覽器讀取數據，這意味着它的並行。

@RequestMapping(value = "downloadFile", method = RequestMethod.GET)
    public StreamingResponseBody getSteamingFile(HttpServletResponse response) throws IOException {
        response.setContentType("application/pdf");
        response.setHeader("Content-Disposition", "attachment; filename=\"demo.pdf\"");
        InputStream inputStream = new FileInputStream(new File("C:\\demo-file.pdf"));
        return outputStream -> {
            int nRead;
            byte[] data = new byte[1024];
            while ((nRead = inputStream.read(data, 0, data.length)) != -1) {
                System.out.println("Writing some bytes..");
                outputStream.write(data, 0, nRead);
            }
        };
    }

Answer 2

您可以嘗試使用apache commons IOUtils。 為什么要重新發明輪子:) 1.打開與遠程服務器的連接2.將inputStream復制到目標文件outputStream。

public void downloadFileFromRemoteLocation(String serverlocation, File destinationFile) throws IOException
{
    try (FileOutputStream fos = new FileOutputStream( destinationFile )){
        URL url = new URL(serverlocation);
        URLConnection connection = url.openConnection();
        IOUtils.copy( connection.getInputStream(),  fos);
    } 
}

如果你想堅持使用Java，那么請看下面的代碼片段

try {
        // Get the directory and iterate them to get file by file...
        File file = new File(fileName);

        if (!file.exists()) {
            context.addMessage(new ErrorMessage("msg.file.notdownloaded"));
            context.setForwardName("failure");
        } else {
            response.setContentType("APPLICATION/DOWNLOAD");
            response.setHeader("Content-Disposition", "attachment"+ 
                                     "filename=" + file.getName());
            stream = new FileInputStream(file);
            response.setContentLength(stream.available());
            OutputStream os = response.getOutputStream();      
            os.close();
            response.flushBuffer();
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (stream != null) {
            try {
                stream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }