Best way to write custom flume NG source/sink

Hello,

I am writing custom flume source and sink and currently I am not seeing a
best way to re-use the existing code. For example, if I am not able to
extend the AvroSource class and customize some functionality easily without
having to copy/paste a lot of existing code. Was it intended to be that way
or am I doing something wrong here ?

Thanks,
Conics