@Override
    public void listFetchers(ListFetchersRequest request,
                             StreamObserver<ListFetchersReply> responseObserver) {
        ListFetchersReply.Builder listFetchersReplyBuilder = ListFetchersReply.newBuilder();
        for (Map.Entry<String, AbstractConfig> fetcherConfig : expiringFetcherStore.getFetcherConfigs()
                .entrySet()) {
            GetFetcherReply.Builder replyBuilder = saveFetcherReply(fetcherConfig);
            listFetchersReplyBuilder.addGetFetcherReplies(replyBuilder.build());
        }
        responseObserver.onNext(listFetchersReplyBuilder.build());
        responseObserver.onCompleted();
    }
FetcherID is key, The pair is the Fetcher object and the Metadata
tika-grpc/src/main/java/org/apache/tika/pipes/grpc/TikaGrpcServerImpl.java