Java 8 streams Map of maps transformation

Java 8 streams

private static void checkTreesForMissingDefinitions(Map<String, String> glossary) {
        
        FinancialTrees.getTrees(false).values().stream()    // Map<IndustryTemplate, Map<FinancialGroup, FinancialTree>>
            .map(Map::values)                               // Stream<Collection<FinancialTree>>
            .flatMap(Collection::stream)                    // Stream<FinancialTree>
            .map(FinancialTree::getAllChildren)             // Stream<List<FinancialTreeNode>> Get nodes fron tree as a List<Node>
            .flatMap(List::stream)                          // Stream<FinancialTreeNode> 
            .map(FinancialTreeNode::getField)               // Stream<FinField>
            .distinct()                                     // remove duplicated fields
            .filter(Objects::nonNull)                       // remove null objects
            .filter(e -> !glossary.containsKey(e.getId()))  // remove fields that have a definition
            .sorted()                                       // sort
            .forEach(System.out::println);                  // logger.log of simply print out fields without definition
                                                            // Alternatively you can .collect(Collectors.toSet()) after last filter.
}


Map<String, Map<Integer, List<Integer>>> map = ...

        List<Integer> keys = map.values()                   // Collection<Map<Integer, List<Integer>>>
                .stream()                                   // Stream<Map<Integer, List<Integer>>>
                .map(Map::keySet)                           // Stream<Set<Integer>>
                .flatMap(Set::stream)                       // Stream<Integer>
                .collect(Collectors.toList());              // List<Integer>

        List<Integer> values = map.values()                 // Collection<Map<Integer, List<Integer>>>
                .stream()                                   // Stream<Map<Integer, List<Integer>>>
                .map(Map::values)                           // Stream<Collection<List<Integer>>>
                .flatMap(Collection::stream)                // Stream<List<Integer>>
                .flatMap(List::stream)                      // Stream<Integer>
                .collect(Collectors.toList());              // List<Integer>