Currently, there are two ways to extend a Java implementation of a Thrift spec: modify the compiler source code or write classes that wrap the existing Java library. The former requires maintaining a fork of Thrift while the latter doesn't allow meaningful changes to, e.g., struct or service classes.
I propose modifying the compiler to include additional annotations to Thrift types (ThriftService, ThriftStruct, etc.) This change would allow much easier extension of generated classes through the use of annotation processors. Happy to supply a patch if it's a desirable improvement. Thanks!