@Override
    public CacheHelper getCoreCacheHelper() {
        // TODO: this is trappy as the expectation is that core keys live for a long
        // time, but here we need to bound it to the lifetime of the wrapped
        // composite reader? Unfortunately some features seem to rely on this...
        return in.getReaderCacheHelper();
    }
This method is sugar for getting an {@link LeafReader} from
an {@link IndexReader} of any kind. If the reader is already atomic,
it is returned unchanged, otherwise wrapped by this class.
tika-eval/tika-eval-app/src/main/java/org/apache/tika/eval/app/tools/SlowCompositeReaderWrapper.java