public JavaContainerBuilder addClasses(Path classFilesDirectory, Predicate<Path> pathFilter)
      throws IOException {
    classpathOrder.add(LayerType.CLASSES);
    return addDirectory(addedClasses, classFilesDirectory, pathFilter);
  }
Adds the contents of a classes directory to the image.

@param classFilesDirectory the directory containing the class files
@param pathFilter filter that determines which files (not directories) should be added
@return this
@throws IOException if adding the layer fails
jib-core/src/main/java/com/google/cloud/tools/jib/api/JavaContainerBuilder.java