Create a temporary file, then upload it using FTP (Java webapp)

Question

Users of my web application have an option to start a process that generates a CSV file (populated by some data from a database) and uploads it to an FTP server (and another department will read the file from there). I'm just trying to figure out how to best implement this. I use commons net ftp functionality. It offers two ways to upload data to the FTP server:

• storeFile(String remote, InputStream local)
• storeFileStream(String remote)

It can take a while to generate all the CSV data so I think keeping a connection open the whole time (storeFileStream) would not be the best way. That's why I want to generate a temporary file, populate it and only then transfer it.

What is the best way to generate a temporary file in a webapp? Is it safe and recommended to use File.createTempFile?

Answer 1

As long as you don't create thousands of CSV files concurrently the upload-time doesn't matter from my point of view. Databases usually output the data row by row and if this is already the format you need for the CSV file I strongly recommend not to use temporary files at all - just do the conversion on-the-fly:

Create an InputStream implementation that reads the database data row by row, converts it to CSV and publish the data via it's read() methods.

BTW: You mentioned that the conversion is done by a web application and that it can take a long time - this can be problematic as the default web client has a timeout. Therefore the long lasting process should be better done by a background thread only triggered by the webapp interface.

Answer 2

It is ok to use createTempFile, new File(tmpDir, UUID.randomUUID().toString()) can do as well. Just do not use deleteOnExit(), it is a leak master. Make sure you delete the file on your right own.

Edit: since you WILL have the data in memory, do not store it anywhere; wrap a java.io.ByteArrayInputSteam and use the method w/ the InputStream. Much neater and better solution.