private static void checkFileRequirements(File src, File dest) throws FileNotFoundException {
        if (src == null) {
            throw new NullPointerException("Source must not be null");
        }
        if (dest == null) {
            throw new NullPointerException("Destination must not be null");
        }
        if (!src.exists()) {
            throw new FileNotFoundException("Source '" + src + "' does not exist");
        }
    }
checks requirements for file copy
@param src the source file
@param dest the destination
@throws FileNotFoundException if the destination does not exist
replugin-host-library/replugin-host-lib/src/main/java/com/qihoo360/replugin/utils/FileUtils.java