Files.copy

A file exists at one location, but we want to copy it to another location. This is a task for Files.copy, a useful method from Java.nio.file.

With this method, we do not need to process the file contents. We do not need to read in the file—this also has speed and memory benefits.

Example program

Here we get two Path objects from the default FileSystem. We then pass these Path objects to Files.copy, which has two arguments.

import java.io.IOException;
import java.nio.file.*;

public class Program {
    public static void main(String[] args) throws IOException {

        // Get paths for input and target files.
        FileSystem system = FileSystems.getDefault();
        Path original = system.getPath("C:\\programs\\file.txt");
        Path target = system.getPath("C:\\programs\\file-2.txt");

        // Copy original to target location.
        Files.copy(original, target);

        // Helpful message.
        System.out.println("File copied!");
    }
}
File copied!

Replace existing file

Here we use a CopyOption as the third argument to Files.copy. CopyOption is an interface—we specify it as a StandardCopyOption.

import java.io.IOException;
import java.nio.file.*;

public class Program {
    public static void main(String[] args) throws IOException {

        // Get paths.
        Path original = FileSystems.getDefault().getPath(
                "C:\\programs\\file.txt");
        Path target = FileSystems.getDefault().getPath(
                "C:\\programs\\file-2.txt");

        // Replace an existing file with REPLACE_EXISTING.
        // ... No FileAlreadyExistsException will be thrown.
        Files.copy(original, target, StandardCopyOption.REPLACE_EXISTING);

        System.out.println("DONE");
    }
}
DONE

Handle exceptions

The Files.copy method can throw exceptions in many circumstances. If the original file is missing, it will cause an IOException.

import java.io.IOException;
import java.nio.file.*;

public class Program {
    public static void main(String[] args) {

        // These files do not exist in our example.
        FileSystem system = FileSystems.getDefault();
        Path original = system.getPath("C:\\programs\\mystery.txt");
        Path target = system.getPath("C:\\programs\\mystery-2.txt");

        try {
            // Throws an exception if the original file is not found.
            Files.copy(original, target, StandardCopyOption.REPLACE_EXISTING);
        } catch (IOException ex) {
            System.out.println("ERROR");
        }
    }
}
ERROR

Programs commonly need to copy files. With Files.copy from java.nio.file, we copy a file at one path to another. Some of the syntax is confusing.

And with file interactions, errors may always occur. These might not be the fault of your program logic. A file might be missing for external reasons.