@Override
    protected void writeMapIdTo(Output output, int fieldNumber, Class<?> clazz)
            throws IOException
    {
        final RegisteredMapFactory factory = mapMapping.get(clazz);
        if (factory == null)
            throw new UnknownTypeException("map: " + clazz);

        output.writeUInt32(fieldNumber, factory.id, false);
    }
Register a {@link Delegate} and assign an id.
<p>
Delegate ids start at 1.
protostuff-runtime-registry/src/main/java/io/protostuff/runtime/ExplicitIdStrategy.java