What is a safe way to create a Temp file in Java?
I'm looking for a safe way to create a temp file in Java. By safe, I mean the following:
- Name should be unique, even under potential race conditions (e.g. another Thread calls the same func at the same time, or another process runs this code simultaneously)
- File should be private, even under potential race conditions (e.g. another user tries to chmod file at high rate)
- I can tell it to delete the file, without me having to do a generic delete, and risk deleting the wrong file
- Ideally, should ensure file is deleted, even if exception is thrown before I get the chance to
- File should default to a sane location (e.g. the JVM specified tmp dir, defaulting to the system temp dir)
Solution 1:
Use File.createTempFile().
File tempFile = File.createTempFile("prefix-", "-suffix");
//File tempFile = File.createTempFile("MyAppName-", ".tmp");
tempFile.deleteOnExit();
Will create a file in the temp dir, like:
prefix-6340763779352094442-suffix
Solution 2:
Since Java 7 there is the new file API "NIO2" which contains new methods for creating temnp files and directories. See
- createTempDirectory
- createTempDirectory
- createTempFile
- createTempFile
e.g.
Path tempDir = Files.createTempDirectory("tempfiles");
or
Path tempFile = Files.createTempFile("tempfiles", ".tmp");
Security notice:
Important difference between File.createTempFile() and Files.createTempFile is also that the latter has more secure permission defaults.
When no file attributes are specified, then the resulting file may have more restrictive access permissions to files created by the
File.createTempFile(String,String,File)method.