@Override
        public java.lang.String getJavaType()
        {
            if (hasOption("ByteBuffer"))
                return "ByteBuffer";
            else
                return "ByteString";
        }
Returns field type for proto files. Scalar value types:
https://developers.google.com/protocol-buffers/docs/proto#scalar

@return .proto type
protostuff-parser/src/main/java/io/protostuff/parser/Field.java