code: public static Mapper mapMapper(final Map map) {
          return new Mapper() {
              public Object map(final Object a) {
                  return map.get(a);
              }
          };
      }
docs: Return a mapper that uses a {@link java.util.Map} instance, and maps keys of that Map to the values.
  @param map a {@link java.util.Map} instance
  @return a Mapper instance