Is there a new Java 8 way of retrieving the file extension?

Not Java8, but you can always use FilenameUtils.getExtension() from apache Commons library. :)

No, see the changelog of the JDK8 release

Actually there is a new way of thinking about returning file extensions in Java 8.

Most of the "old" methods described in the other answers return an empty string if there is no extension, but while this avoids NullPointerExceptions, it makes it easy to forget that not all files have an extension. By returning an Optional, you can remind yourself and others about this fact, and you can also make a distinction between file names with an empty extension (dot at the end) and files without extension (no dot in the file name)

public static Optional<String> findExtension(String fileName) {
    int lastIndex = fileName.lastIndexOf('.');
    if (lastIndex == -1) {
        return Optional.empty();
    }
    return Optional.of(fileName.substring(lastIndex + 1));
}

No there is no more efficient/convenient way in JDK, but many libraries give you ready methods for this, like Guava: Files.getFileExtension(fileName) which wraps your code in single method (with additional validation).