What is a safe way to create a Temp file in Java?

Question

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)

Answer 1

NIO.2

Since Java 7 there is the new file API "NIO2" which contains new methods for creating temp files and directories.

Modern	Use default temp folder	Specify folder
Create folder	Files.createTempDirectory	Files.createTempDirectory
Create file	Files.createTempFile	Files.createTempFile

e.g.

Path tempDir = Files.createTempDirectory("tempfiles");

or

Path tempFile = Files.createTempFile("file", ".tmp");

For more info:

• Oracle’s online tutorial, free-of-cost: File I/O (Featuring NIO.2)
• Oracle technical notes: NIO and NIO.2 Examples
• What Is the Difference Between NIO and NIO.2? at Baeldung.com.
• Introduction to the Java NIO2 File API at Baeldung.com.

Legacy

Before Java 7, you might use the legacy methods createTempFile found on the File class. Notice the name “File” is singular, in contrast to the Files class in modern NIO.2.

Legacy	Use default temp folder	Specify folder
Create folder	—	—
Create file	File.createTempFile	File.createTempFile

Security note

An 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.

Answer 2

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