@Override
    public Registration readClass(Input input) {
      Registration reg = super.readClass(input);
      if (reg != null) {
        ponderGlobalPreReadHook(reg.getType()); // Needed to intercept readClassAndObject.
      }
      return reg;
    }
Provides general-purpose hooks for specific types, as well as a global hook.
ql/src/java/org/apache/hadoop/hive/ql/exec/SerializationUtilities.java