Trail: Essential Java Classes

Lesson: Basic I/O

Section: File I/O (Featuring NIO.2)

The Java Tutorials have been written for JDK 8. Examples and practices described in this page don’t take advantage of improvements introduced in later releases and might use technology no longer available. See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases. See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

Copying a File or Directory

You can copy a file or directory by using the
copy(Path, Path, CopyOption...) method. The copy fails if the target file exists, unless the REPLACE_EXISTING option is specified.

Directories can be copied. However, files inside the directory are not copied, so the new directory is empty even when the original directory contains files.

When copying a symbolic link, the target of the link is copied. If you want to copy the link itself, and not the contents of the link, specify either the NOFOLLOW_LINKS or REPLACE_EXISTING option.

This method takes a varargs argument. The following StandardCopyOption and LinkOption enums are supported:

• REPLACE_EXISTING – Performs the copy even when the target file already exists. If the target is a symbolic link, the link itself is copied (and not the target of the link). If the target is a non-empty directory, the copy fails with the DirectoryNotEmptyException exception.
• COPY_ATTRIBUTES – Copies the file attributes associated with the file to the target file. The exact file attributes supported are file system and platform dependent, but last-modified-time is supported across platforms and is copied to the target file.
• NOFOLLOW_LINKS – Indicates that symbolic links should not be followed. If the file to be copied is a symbolic link, the link is copied (and not the target of the link).

If you are not familiar with enums, see
Enum Types.

The following shows how to use the copy method:

import static java.nio.file.StandardCopyOption.*;
...
Files.copy(source, target, REPLACE_EXISTING);

In addition to file copy, the Files class also defines methods that may be used to copy between a file and a stream. The
copy(InputStream, Path, CopyOptions...) method may be used to copy all bytes from an input stream to a file. The
copy(Path, OutputStream) method may be used to copy all bytes from a file to an output stream.

The
Copy example uses the copy and Files.walkFileTree methods to support a recursive copy. See
Walking the File Tree for more information.