Java File createTempFile() method with examples

November 30, 2019 No comments Java IO Examples createTempFile

1. Introduction

The createTempFile() method creates an empty file in the temporary directory which commonly is a /tmp or /var/tmp in Linux and C:\Users\<username>\AppData\Local\Temp in Windows. The method accepts also the third parameter where we can specify a different folder in which the file will be generated. Two first parameters are prefix and suffix that will be used for generating the file's name. Note that the prefix and the suffix may first be adjusted to fit the limitations of the operating system. The name of the new file will be generated by concatenating the prefix, five or more internally-generated characters, and the suffix.

2. Method signature

createTempFile takes two or three parameters. The third parameter is a directory in which the file will be generated.

createTempFile(prefix, suffix, null) is the same as createTempFile(prefix, suffix).

public static File createTempFile(String prefix, String suffix) throws IOException
public static File createTempFile(String prefix, String suffix, File directory) throws IOException

Parameters:

  • prefix - prefix string to be used in generating the file's name; this argument must be at least three characters long
  • suffix - suffix string to be used in generating the file's name; if null then the default suffix ".tmp" will be used

  • directory - directory in which the file should be created, if this parameter is null the default temporary folder will be used

Returns

  • File - a newly-created empty file

Throws

  • IllegalArgumentException - if the prefix parameter contains fewer than three characters
  • IOException - in case the file could not be created
  • SecurityException - when security manager does not allow to create a file

3. Examples

3.1. The program that creates an empty file in the temporary directory

package com.frontbackend.java.io.examples;

import java.io.File;

public class FrontBackend {

    public static void main(String args[]) {

        try {
            File file = File.createTempFile("frontbackend", ".txt");

            System.out.println(file.getAbsolutePath());

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The output:

/tmp/frontbackend6591641783176241525.txt

3.2. Program that creates file using createTempFile() in /var/tmp directory

package com.frontbackend.java.io.examples;

import java.io.File;

public class FrontBackend {

    public static void main(String args[]) {

        try {
            File file = File.createTempFile("frontbackend", ".txt", new File("/var/tmp"));

            System.out.println(file.getAbsolutePath());

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

The output:

/var/tmp/frontbackend2899620267305156807.txt

4. Conclusion

In this article we presented File.createTempFile() a method that creates an empty file in a temporary directory. We can use this method also to generate a file in any other directory, using the third parameter. Creating and using temporary files are common operations used in complex systems where we must store a partially computed date on the filesystem to improve performance.

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