public void writeTo(Output output, T message)
                        throws IOException
                {
                    final Enum<?> existing;
                    try
                    {
                        existing = (Enum<?>) f.get(message);
                    }
                    catch (IllegalAccessException e)
                    {
                        throw new RuntimeException(e);
                    }
                    catch (IllegalArgumentException e)
                    {
                        throw new RuntimeException(e);
                    }

                    if (existing != null)
                        eio.writeTo(output, number, repeated, existing);
                }
Field factory via plain old reflection api.

@author David Yu
@created Jul 7, 2011
protostuff-runtime/src/main/java/io/protostuff/runtime/RuntimeReflectionFieldFactory.java