code: def CreateJarBuilder(env):
      
      try:
          java_jar = env['BUILDERS']['JarFile']
      except KeyError:
          fs = SCons.Node.FS.get_default_fs()
          jar_com = SCons.Action.Action('$JARCOM', '$JARCOMSTR')
          java_jar = SCons.Builder.Builder(action = jar_com,
                                           suffix = '$JARSUFFIX',
                                           src_suffix = '$JAVACLASSSUFFIX',
                                           src_builder = 'JavaClassFile',
                                           source_factory = fs.Entry)
          env['BUILDERS']['JarFile'] = java_jar
      return java_jar
docs: The Jar builder expects a list of class files
      which it can package into a jar file.
  
      The jar tool provides an interface for passing other types
      of java files such as .java, directories or swig interfaces
      and will build them to class files in which it can package
      into the jar.