How to avoid delete the Temp files using java?

Question

I have a simple code to generate the temp files and store the some values(I don't want to store the files in normal storage area) In future, I want to use that file and get the data from that file (its not a problem if the user manually delete the files). But I don't want to delete the files automatically. when read this link, I get some information, generally temp files not deleted when you explicitly call deleteOnExit() but when my JVM finish the work temp file deleted automatically.

//create a temp file
File temp = File.createTempFile("demo_", ".txt");
String path = temp.getParent();

//count the file which names starts with "demo"
File f = new File(path);
File[] matchingFiles = f.listFiles(new FilenameFilter() {
public boolean accept(File dir, String name) {
    return name.startsWith("demo") && name.endsWith(".txt");
}
});

// Print count array elements
    System.out.println("Length : " + matchingFiles.length + " ");

Here I never call the deleteOnExit() (but file delete automtically)OR JVM automatically delete the file? By the way its deleted automatically if is it possible to avoid deleting the file? or any other ways to do my requirement?

I tried your code on Windows and the file is not deleted after the program exits. What operating system are you running this on? Does the OS have a temp-file cleanup process running continuously? — Jim Garrison
– Jim Garrison, Commented Nov 25, 2017 at 7:14

Basil Bourque · Accepted Answer · 2025-05-04 16:26:06Z

2

Creating temp file does not imply deleting

File.createTempFile only creates files with unique names, other than that they are just regular files. They are not deleted automatically. Ditto for the newer Files.createTempFile

It is explained in the Javadoc:

This method provides only part of a temporary-file facility. To arrange for a file created by this method to be deleted automatically, use the deleteOnExit() method.

edited May 4 at 16:26

Basil Bourque

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answered Nov 25, 2017 at 5:05

Evgeniy Dorofeev

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11 Comments

Moorthy Over a year ago

Thanks for expatiation, its nice. so file will be deleted autoamatically right??/if i want to want to create the undeleted temp files means how to dot that?

Evgeniy Dorofeev Over a year ago

no, by default it wil not be deleted on exit. only if you explicitly call deleteOnExit

Moorthy Over a year ago

BUT how i never call deleteOnExit () method in my code still my files deleted. why?How??

Evgeniy Dorofeev Over a year ago

Are you sure it is deleted? Temp files are created in user's temp folder. Add System.out.println(temp); to your code and see where it is created

Jim Garrison Over a year ago

WARNING Do not use deleteOnExit() in a system designed to remain active for long periods of time -- i.e. a web application. Files to be deleted are stored in a Map, and if the application never exits the map will eventually fill up all available memory and crash the system. This is a known restriction of deleteOnExit().

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