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).

Answer 1

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

Answer 2

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);
}

Answer 3

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)
    {
    }
}

Answer 4

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).

Answer 5

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);
    }
}

Answer 6

If you are already using Guava:

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

Answer 7

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

public static void touch(final Path path) throws IOException {
    Objects.requireNotNull(path, "path is null");
    if (Files.exists(path)) {
        Files.setLastModifiedTime(path, FileTime.from(Instant.now()));
    } else {
        Files.createFile(path);
    }
}