@Override
    protected void writeMapIdTo(Output output, int fieldNumber, Class<?> clazz)
            throws IOException
    {
        final MapSchema.MessageFactory factory = mapMapping.get(clazz);
        if (factory == null && clazz.getName().startsWith("java.util")
            && MapSchema.MessageFactories.accept(clazz.getSimpleName()))
        {
            // jdk map
            // better not to register the jdk map if using this strategy
            // as it saves space by not writing the full package
            output.writeString(fieldNumber, clazz.getSimpleName(), false);
        }
        else
        {
            output.writeString(fieldNumber, clazz.getName(), false);
        }
    }
Used by {@link RuntimeSchema#map(Class, Class)}.
protostuff-runtime/src/main/java/io/protostuff/runtime/DefaultIdStrategy.java