How to Implement a Simple File Download Servlet?

Implement a Simple File Download Servlet

To implement a simple file download servlet, follow these steps:

1. Create a Servlet:

   • In web.xml, register a servlet with the URL pattern /download.

2. Implement the Servlet:

   • In the doGet() method, retrieve the file ID from the request.
   • Query the database for the file name and type using the file ID.
   • Set the Content-Type header to specify the file type (e.g., application/pdf).
   • Set the Content-disposition header to instruct the browser to download the file (e.g., attachment; filename=yourcustomfilename.pdf).
   • Retrieve the file from the file system based on the file name.
   • Send the file contents to the response output stream in chunks.

Here's an example servlet implementation:

public class DownloadServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String id = request.getParameter("id");
        // Retrieve file name and type using ID from database
        response.setContentType("fileType");
        response.setHeader("Content-disposition", "attachment; filename=yourcustomfilename.pdf");
        File file = new File("fileName");
        OutputStream out = response.getOutputStream();
        try (FileInputStream in = new FileInputStream(file)) {
            byte[] buffer = new byte[4096];
            int length;
            while ((length = in.read(buffer)) > 0) {
                out.write(buffer, 0, length);
            }
        } finally {
            out.flush();
        }
    }
}

The above is the detailed content of How to Implement a Simple File Download Servlet?. For more information, please follow other related articles on the PHP Chinese website!