java stream 分组统计

文章来源：https://gitee.com/wustrive/codes/l1typxfn79adhs0czmwb313

public void testStreamGroupBy() {
        List<Map<String, Object>> items = Lists.newArrayList();
        Map<String, Object> map = Maps.newHashMap();
        map.put("daily", "2018-01-10");
        map.put("count", 20);
        items.add(map);
        map = Maps.newHashMap();
        map.put("daily", "2018-01-11");
        map.put("count", 80);
        items.add(map);
        map = Maps.newHashMap();
        map.put("daily", "2018-01-12");
        map.put("count", 21);
        items.add(map);
        map = Maps.newHashMap();
        map.put("daily", "2018-01-10");
        map.put("count", 28);
        items.add(map);
        final List<Map<String, Object>> newItems = Lists.newArrayList();
		//方式一： 使用遍历
		for (int i = 0; i < result.size(); i++) {
            Map<String, Object> oldMap = result.get(i);
            boolean isContain = false;
            for (int j = 0; j < newList.size(); j++) {
                Map<String, Object> newMap = newList.get(j);
                if (newMap.get("daily").equals(oldMap.get("daily"))) {
                    for (String key : oldMap.keySet()) {
                        newMap.put(key, oldMap.get(key));
                        oldMap.put("count", (int) newMap.get("count") + (int) oldMap.get("count"));
                    }
                    isContain = true;
                    break;
                }
            }
            if (!isContain) {
                newItems .add(oldMap);
            }
        }
        System.out.println("方式一：" + newItems );
        
		//方式二：使用1.8 stream流
        Map<Object, Integer> sum = items.stream().collect(Collectors.groupingBy(m -> m.get("daily"), Collectors.summingInt(p -> ConvertUtil.obj2Int(p.get("count")))));
        sum.forEach((k, v) -> {
            newItems.add(ImmutableMap.of("daily", String.valueOf(k), "count", String.valueOf(v)));
        });

        System.out.println("方式二："+newItems);
    }