Standard concise way to copy a file in Java?

I would avoid the use of a mega api like apache commons. This is a simplistic operation and its built into the JDK in the new NIO package. It was kind of already linked to in a previous answer, but the key method in the NIO api are the new functions "transferTo" and "transferFrom".

http://java.sun.com/javase/6/docs/api/java/nio/channels/FileChannel.html#transferTo(long,%20long,%20java.nio.channels.WritableByteChannel)

One of the linked articles shows a great way on how to integrate this function into your code, using the transferFrom:

public static void copyFile(File sourceFile, File destFile) throws IOException {
    if(!destFile.exists()) {
        destFile.createNewFile();
    }

    FileChannel source = null;
    FileChannel destination = null;

    try {
        source = new FileInputStream(sourceFile).getChannel();
        destination = new FileOutputStream(destFile).getChannel();
        destination.transferFrom(source, 0, source.size());
    }
    finally {
        if(source != null) {
            source.close();
        }
        if(destination != null) {
            destination.close();
        }
    }
}

Learning NIO can be a little tricky, so you might want to just trust in this mechanic before going off and trying to learn NIO overnight. From personal experience it can be a very hard thing to learn if you don't have the experience and were introduced to IO via the java.io streams.


As toolkit mentions above, Apache Commons IO is the way to go, specifically FileUtils.copyFile(); it handles all the heavy lifting for you.

And as a postscript, note that recent versions of FileUtils (such as the 2.0.1 release) have added the use of NIO for copying files; NIO can significantly increase file-copying performance, in a large part because the NIO routines defer copying directly to the OS/filesystem rather than handle it by reading and writing bytes through the Java layer. So if you're looking for performance, it might be worth checking that you are using a recent version of FileUtils.


Now with Java 7, you can use the following try-with-resource syntax:

public static void copyFile( File from, File to ) throws IOException {

    if ( !to.exists() ) { to.createNewFile(); }

    try (
        FileChannel in = new FileInputStream( from ).getChannel();
        FileChannel out = new FileOutputStream( to ).getChannel() ) {

        out.transferFrom( in, 0, in.size() );
    }
}

Or, better yet, this can also be accomplished using the new Files class introduced in Java 7:

public static void copyFile( File from, File to ) throws IOException {
    Files.copy( from.toPath(), to.toPath() );
}

Pretty snazzy, eh?