treemultimap

Exploring basic features of guava's TreeMultimap.

preface

TreeMultimap is an implementation of Multimap whose keys and values are ordered by their natural ordering or by supplied comparators.
Warning: The comparators or comparables used must be consistent with equals as explained by the Comparable class specification. Otherwise, the resulting multiset will violate the general contract of SetMultimap, which it is specified in terms of Object.equals(java.lang.Object).

SetMultimap contract: Since the value collections are sets, the behavior of a SetMultimap is not specified if key or value objects already present in the multimap change in a manner that affects equals comparisons. Use caution if mutable objects are used as keys or values in a SetMultimap.

manual

• build.gradle

  compile group: 'com.google.guava', name: 'guava', version: '25.1-jre'
  

• TreeMultimap creation

  TreeMultimap<X, Y> customerEvents =
          TreeMultimap.create(keyComparator, valueComparator);
  

project description

• CustomerEvent - events that are published:

  int customerId;
  CustomerEventDetails details;
  

  where CustomerEventDetails is:

  String message;
  LocalDateTime dateTime;
  

• CustomerEventPublisher publishes CustomerEvent using guava's EventBus
• CustomerEventsSortedMap listens to published CustomerEvent, and add them to TreeMultimap
  • defining multimap (sorted by dateTime from CustomerEventDetails):

    TreeMultimap<Integer, CustomerEventDetails> customerEvents =
        TreeMultimap.create(Comparator.naturalOrder(), Comparator.comparing(CustomerEventDetails::getDateTime));
    

  • listening:

    @Subscribe
    void add(@NonNull CustomerEvent event) {
        Preconditions.checkArgument(nonNull(event.getDetails()));
        Preconditions.checkArgument(nonNull(event.getDetails().getDateTime()));
     
        customerEvents.put(event.getCustomerId(), event.getDetails());
    }     
    

• binding publisher to listener:
  • producing EventBus:

    public static EventBus customerEventsSortedMapBus(CustomerEventsSortedMap map) {
         EventBus bus = new EventBus();
         bus.register(map);
         return bus;
    }    
    

  • binding to publisher:

    def customerEventsSortedMap = new CustomerEventsSortedMap()
    def bus = BusFactory.customerEventsSortedMapBus(customerEventsSortedMap)
    def customerEventPublisher = new CustomerEventPublisher(bus)        
    

tests

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