How to Efficiently Download Generated PDF Files from Spring Controllers?

Downloading PDF Files from Spring Controllers

Background:

Downloading files efficiently from web applications is a common requirement. This article addresses the challenge of downloading generated PDF files from Spring controllers.

Generating PDF Files:

To generate PDF files, consider using a combination of Freemarker templates and a PDF generation framework such as iText. This allows for dynamic generation of PDF content based on user input or other data.

Downloading Files through Controllers:

To enable file downloads through Spring controllers:

1. Create a Controller Method:
   Create a controller method that handles the download request. Typically, this involves using the @RequestMapping annotation to map the method to a specific request path. For example:

   @RequestMapping(value = "/download/pdf/{fileName}", method = RequestMethod.GET)
   public void downloadPdf(@PathVariable("fileName") String fileName, HttpServletResponse response) {
   ...
   }

2. Get the File Data:
   Obtain the PDF data as an InputStream. This may involve invoking your PDF generation logic or fetching the file from a storage location.

3. Configure the Response:
   Set the response headers to indicate the file type and specify the file name for saving. For PDF files, use:

   response.setContentType("application/pdf");
   response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");

4. Copy the File Data to the Response:
   Use the org.apache.commons.io.IOUtils.copy method to transfer the PDF data from the input stream to the response's output stream:

   IOUtils.copy(inputStream, response.getOutputStream());

5. Flush the Response:
   Flush the response to send the PDF file to the client. This initiates the download process.

Example Code:

The following code snippet demonstrates the implementation of a controller method for PDF file downloads:

@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
      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");
    }

}

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