map的求和和排序

  //前台出过来的参数为以下样子
{"fruitList":[{"name":"apple","answer":"1"},
{"name":"apple","answer":"2"},
{"name":"apple","answer":"3"},
{"name":"apple","answer":"3"},
{"name":"apple","answer":"4"},
{"name":"orange","answer":"1"},	
{"name":"orange","answer":"2"},
{"name":"orange","answer":"3"},
{"name":"orange","answer":"3"},
{"name":"orange","answer":"4"},
{"name":"banana","answer":"1"},	
{"name":"banana","answer":"2"},
{"name":"banana","answer":"3"}]

  Map<String, Integer> map = new HashMap<>();
        // 需要算每一中水果总有多少个。
        //第一种。
        for (FruitEntity fruitEntity : fruitList) {

            if (map.containsKey(fruitEntity.getName())) {
                Integer numBefore = map.get(fruitEntity.getNumber());
                Integer numCurent = fruitEntity.getNumber();
                map.put(fruitEntity.getName(), numBefore + numCurent);
            } else {
                map.put(fruitEntity.getName(), fruitEntity.getNumber());
            }
        }
        //第二种
        //需要注意一下
        //        BigDecimal::add
        //        Integer::sum
        fruitList.forEach(fruitEntity ->
                map.merge(fruitEntity.getName(), fruitEntity.getNumber(), Integer::sum)
        );

        //根据水果的数量进行一下排序的方法。
        List<String> list = map.entrySet().stream()
                .sorted(Map.Entry.<String, Integer>comparingByValue()
                        .reversed())
                .map(entry -> entry.getKey()).collect(Collectors.toList());