How to use a save file dialog from a servlet?

Question

I am trying to let the user save data from my servlet as a CSV file. Originally I was just locating their desktop to drop the file, but permission would be denied with this route so I want to ask the user where they want to save it.

From what I am seeing, I cannot use the Swing API in a servlet because Tomcat does not know how to draw the GUI. I tried this code:

    String fileName = "ClassMonitor" + formatter.format(currentDate) + ".csv";

    File csvFile = new File(fileName);

    //Attempt to write as a CSV file 
    try{

        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setSelectedFile(csvFile);
        int returnValue = fileChooser.showSaveDialog(null);

        if(returnValue == JFileChooser.APPROVE_OPTION)
        {
            BufferedWriter out = new BufferedWriter(new FileWriter(csvFile));

            //Iterates and writes to file
            for(ClassInfo classes : csvWrite)
            {
                //Check if the class has a comma. Currently, only section titles have a comma in them, so that's all we check for.
                classes.setSectionTitle(replaceComma(classes.getSectionTitle()));

                out.write(classes.toString());
            }

            //Close the connection
            out.close();
        }

        //Log the process as successful.
        logger.info("File was successfully written as a CSV file to the desktop at " + new Date() + "\nFilename" +
                "stored as " + fileName + ".");

    }
    catch(FileNotFoundException ex)
    {
        //Note the exception
        logger.error("ERROR: I/O exception has occurred when an attempt was made to write results as a CSV file at " + new Date());
    }
    catch(IOException ex)
    {
        //Note the exception
        logger.error("ERROR: Permission was denied to desktop. FileNotFoundException thrown.");
    }
    catch(Exception ex)
    {
        //Note the exception
        logger.error("ERROR: Save file was not successfull. Ex: " + ex.getMessage());
    }



}

But this will throw a headlessException.

Any guidance on how to implement something like a save file dialog in a servlet would be appreciated.

Answer 1

Just write it to the response body instead of to the local(!!) disk file system.

response.setContentType("text/csv"); // Tell browser what content type the response body represents, so that it can associate it with e.g. MS Excel, if necessary.
response.setHeader("Content-Disposition", "attachment; filename=name.csv"); // Force "Save As" dialogue.
response.getWriter().write(csvAsString); // Write CSV file to response. This will be saved in the location specified by the user.

The Content-Disposition: attachment header takes care of the Save As magic.

See also:

• JSP generating Excel spreadsheet (XLS) to download

Answer 2

You can't call the JFileChooser from the servlet because the servlet runs on the server, not on the client; all of your Java code is executed on the server. If you want to save the file on the server, you need to already know the path you want to write to.

If you want to prompt the user's browser to save the file, use the content-disposition header: Uses of content-disposition in an HTTP response header