public Map<String, SubjectDataContainer> loadAllFromFile(String collectionIdentifier) {
        Path collection = this.container.resolve(collectionIdentifier);
        if (!Files.exists(collection)) {
            return Collections.emptyMap();
        }

        Map<String, SubjectDataContainer> holders = new HashMap<>();
        try (Stream<Path> s = Files.list(collection)){
            s.filter(p -> p.getFileName().toString().endsWith(".json"))
                    .forEach(subjectFile -> {
                        try {
                            LoadedSubject sub = loadFromFile(subjectFile);
                            if (sub != null) {
                                holders.put(sub.identifier, sub.data);
                            }
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    });
        } catch (IOException e) {
            e.printStackTrace();
        }
        return holders;
    }
Loads all known subjects for a given collection

@param collectionIdentifier the collection identifier
@return a map of found subjects
sponge/src/main/java/me/lucko/luckperms/sponge/service/model/persisted/SubjectStorage.java