@Override
    protected <T> HasSchema<T> transferPojoId(Input input, Output output,
            int fieldNumber) throws IOException
    {
        final String className = input.readString();

        final HasSchema<T> wrapper = getSchemaWrapper(className,
                0 != (AUTO_LOAD_POLYMORPHIC_CLASSES & flags));
        if (wrapper == null)
        {
            throw new ProtostuffException("polymorphic pojo not registered: "
                    + className);
        }

        output.writeString(fieldNumber, className, false);

        return wrapper;
    }
Used by {@link RuntimeSchema#map(Class, Class)}.
protostuff-runtime/src/main/java/io/protostuff/runtime/DefaultIdStrategy.java