Simulate touch command with Java

Question

I want to change modification timestamp of a binary file. What is the best way for doing this?

Would opening and closing the file be a good option? (I require a solution where the modification of the timestamp will be changed on every platform and JVM).

Someone should submit this as an enhancement request to unix4j: https://github.com/tools4j/unix4j — Sridhar Sarnobat, May 21 '17 at 05:37
I do not understand the the relation between the title and the question here? — Lealo, Sep 28 '17 at 19:29
@Lealo see [Unix touch command](https://en.wikipedia.org/wiki/Touch_(Unix)) — GreenGiant, Jul 09 '18 at 20:31
The title is confusing, as is the accepted answer. Touch *creates* a file if it does not exist. The title should be changed. — user239558, Jul 12 '18 at 08:22

score 50 · Accepted Answer · edited Sep 02 '14 at 08:19

50

The File class has a setLastModified method. That is what ANT does.

edited Sep 02 '14 at 08:19

Mmmh mmh

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answered Sep 10 '09 at 17:07

Yishai

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3

Except that there is known Android bug, and File.setLastModified doesn't do anything on most Android devices. – Pointer Null Dec 19 '15 at 17:57
14

And except shell `touch` creates the file, and this doesn't. – Victor Sergienko Aug 07 '16 at 21:58

score 28 · Answer 2 · edited May 23 '17 at 12:02

28

My 2 cents, based on @Joe.M answer

public static void touch(File file) throws IOException{
    long timestamp = System.currentTimeMillis();
    touch(file, timestamp);
}

public static void touch(File file, long timestamp) throws IOException{
    if (!file.exists()) {
       new FileOutputStream(file).close();
    }

    file.setLastModified(timestamp);
}

edited May 23 '17 at 12:02

Community

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answered Sep 02 '14 at 15:02

Mmmh mmh

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sdgfsdh · Answer 3 · 2023-03-13T15:36:26.273

18

Since File is a bad abstraction, it is better to use Files and Path:

public static void touch(final Path path) throws IOException {
    Objects.requireNonNull(path, "path is null");
    try {
        Files.createFile(path);
    } catch (FileAlreadyExistsException e) {
        Files.setLastModifiedTime(path, FileTime.from(Instant.now()));
    }
}

edited Mar 13 '23 at 15:36

answered Jun 05 '17 at 16:59

sdgfsdh

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`Files.createFile(Path)` also checks for existence of the file. This check and the creation are an atomic operation. I think it’s better to always use `Files.createFile(Path)` and use `Files.setLastModifiedTime` if a `java.nio.file.FileAlreadyExistsException` is thrown. Or use `Path.toFile().createNewFile()` which also does the check and creation in an atomic operation, but uses a `boolean` return code instead of an exception to indicate if the file already existed. – Martin Mar 13 '23 at 12:41
@Martin Good point. I have updated the answer to be atomic. It still might fail if (somehow) the file is deleted between the `try` and `catch` though. – sdgfsdh Mar 13 '23 at 16:18

score 12 · Answer 4 · answered Mar 30 '13 at 17:49

12

Here's a simple snippet:

void touch(File file, long timestamp)
{
    try
    {
        if (!file.exists())
            new FileOutputStream(file).close();
        file.setLastModified(timestamp);
    }
    catch (IOException e)
    {
    }
}

answered Mar 30 '13 at 17:49

Zach-M

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10

Why not `file.createNewFile()` instead of `new FileOutputStream(file).close()`? – Harvey Aug 20 '15 at 19:04

score 8 · Answer 5 · edited Jan 26 '11 at 00:33

I know Apache Ant has a Task which does just that.
See the source code of Touch (which can show you how they do it)

They use FILE_UTILS.setFileLastModified(file, modTime);, which uses ResourceUtils.setLastModified(new FileResource(file), time);, which uses a org.apache.tools.ant.types.resources.Touchable, implemented by org.apache.tools.ant.types.resources.FileResource...

Basically, it is a call to File.setLastModified(modTime).

score 6 · Answer 6 · answered Jul 24 '13 at 16:42

This question only mentions updating the timestamp, but I thought I'd put this in here anyways. I was looking for touch like in Unix which will also create a file if it doesn't exist.

For anyone using Apache Commons, there's FileUtils.touch(File file) that does just that.

Here's the source from (inlined openInputStream(File f)):

public static void touch(final File file) throws IOException {
    if (file.exists()) {
        if (file.isDirectory()) {
            throw new IOException("File '" + file + "' exists but is a directory");
        }
        if (file.canWrite() == false) {
            throw new IOException("File '" + file + "' cannot be written to");
        }
    } else {
        final File parent = file.getParentFile();
        if (parent != null) {
            if (!parent.mkdirs() && !parent.isDirectory()) {
                throw new IOException("Directory '" + parent + "' could not be created");
            }
        }
        final OutputStream out = new FileOutputStream(file);
        IOUtils.closeQuietly(out);
    }
    final boolean success = file.setLastModified(System.currentTimeMillis());
    if (!success) {
        throw new IOException("Unable to set the last modification time for " + file);
    }
}

There is a race condition between the file.exists and file.setLastModified calls. I.e. this code gets it backwards: FIRST you go ahead and try, THEN you do the post-mortem diagnostics. — toolforger, Apr 17 '18 at 12:44

score 6 · Answer 7 · answered Dec 14 '15 at 11:35

6

If you are already using Guava:

com.google.common.io.Files.touch(file)

answered Dec 14 '15 at 11:35

Joe23

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Simulate touch command with Java

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