How to Download Files Generated Dynamically Using Spring Controllers?

Downloading Files from Spring Controllers

Many applications require the download of files from a website. In some cases, these files are generated dynamically using a framework such as Freemarker and a PDF generation library like iText. However, this raises the issue of how to allow users to download the file through a Spring Controller.

The solution involves using the HttpServletResponse object to write the file to the output stream. This can be achieved with the following code:

@RequestMapping(value = "/files/{file_name}", method = RequestMethod.GET)
public void getFile(
    @PathVariable("file_name") String fileName, 
    HttpServletResponse response) {
    try {
      // get your file as InputStream
      InputStream is = ...;
      // copy it to response's OutputStream
      org.apache.commons.io.IOUtils.copy(is, response.getOutputStream());
      response.flushBuffer();
    } catch (IOException ex) {
      log.info("Error writing file to output stream. Filename was '{}'", fileName, ex);
      throw new RuntimeException("IOError writing file to output stream");
    }

}

Once the output stream is accessible, it can be used as the destination for the PDF generated by the PDF generator. Additionally, by setting the Content-Type to "application/pdf," the correct file type can be specified for the browser.

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