Java Cookbook

Creating a Transient File

Problem

You need to create a file with a unique temporary filename or arrange for a file to be deleted when your program is finished.

Solution

Use a java.io.File object’s createTempFile( ) or deleteOnExit( ) method.

Discussion

The File object has a createTempFile method and a deleteOnExit method. The former creates a file with a unique name -- in case several users run the same program at the same time on a server -- and the latter arranges for any file (no matter how it was created) to be deleted when the program exits. Here we arrange for a backup copy of a program to be deleted on exit, and we also create a temporary file and arrange for it to be removed on exit. Sure enough, both files are gone after the program runs.

import java.io.*; /** * Work with temporary files in Java. */ public class TempFiles { public static void main(String[] argv) throws IOException { // 1. Make an existing file temporary // Construct a File object for the backup created by editing // this source file. The file probably already exists. // My editor creates backups by putting ~ at the end of the name. File bkup = new File("Rename.java~"); // Arrange to have it deleted when the program ends. bkup.deleteOnExit( ); // 2. Create a new temporary file. // Make a file object for foo.tmp, in the default temp directory File tmp = File.createTempFile("foo", "tmp"); // Report on the filename that it made up for us. System.out.println("Your temp file is " + tmp.getCanonicalPath( )); // ...