Group and Sum By Id

GroupAndSumById.java

private Map<Integer, Integer> getGroupsById() {
    List<IdValue> values = Lists.newArrayList(
      new IdValue(1, 2),
      new IdValue(1, 6),
      new IdValue(3, 1),
      new IdValue(3, 3),
      new IdValue(5, 3),
      new IdValue(5, 10)
    );

    Map<Integer, Integer> collect = values.stream()
                                          .collect(Collectors.groupingBy(IdValue::getId, Collectors.toList()))
                                          .entrySet()
                                          .stream()
                                          .collect(Collectors.toMap(
                                                     Map.Entry::getKey,
                                                     entry -> entry.getValue()
                                                                   .stream()
                                                                   .mapToInt(IdValue::getValue)
                                                                   .sum()
                                                   )
                                          );

    collect.forEach((key, value) -> log.info("group ==> {} {} ", key, value));
    return collect;
}

  private static class IdValue {
    private int id;
    private int value;

    public IdValue(int id, int value) {
      this.id = id;
      this.value = value;
    }

    public int getId() {
      return id;
    }

    public void setId(int id) {
      this.id = id;
    }

    public int getValue() {
      return value;
    }

    public void setValue(int value) {
      this.value = value;
    }
  }