This getClean_visible method is specific to the Java implementation of thrift. Have you tried accessing StreamItem.body.clean_visible directly?
Can you try writing a test for this in Java?
The test can create a StreamItem with a long clean_visible property, and serialize it out to a file, and then read it back in, and check the length using this method?
If that fails, then we should ask the thrift users list at apache.