Java8-Map数据处理

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互联网集市收集整理的这篇技术教程文章主要介绍了Java8-Map数据处理，小编现在分享给大家，供广大互联网技能从业者学习和参考。文章包含3217字，纯文字阅读大概需要5分钟。

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Map<String, Area> map = new LinkedHashMap<>();
Area a1 = new Area(1, 10L, "河南", new BigDecimal(100), 1);
Area a2 = new Area(2, 20L, "江西", new BigDecimal(200), 2);
Area a3 = new Area(3, 30L, "北京", new BigDecimal(300), 3);
Area a4 = new Area(4, 40L, "天津", new BigDecimal(400), 1);
Area a5 = new Area(4, 40L, "天津", new BigDecimal(400), 1);
map.put("101", a1);
map.put("102", a2);
map.put("103", a3);
map.put("105", a5);
map.put("104", a4);

Map<String, Double> singleMap = new LinkedHashMap<>();
singleMap.put("100", 0.08);
singleMap.put("101", 0.1);
singleMap.put("103", 0.2);
singleMap.put("102", 0.91);


// map 迭代循环 key value
map.forEach((key, value) -> {
    System.out.println(key + "：" + value);
});

// map对象value转化为list集合
List<Area> valueList = map.values().stream().collect(Collectors.toList());
System.out.println("map对象value转化为list集合 = " + valueList);

// map对象key转化为list集合
List<String> keyList = map.keySet().stream().collect(Collectors.toList());
System.out.println("map对象key转化为list集合 = " + keyList);


Map<String, Area> keyAsc = Java8MapUtil.sortByKeyAsc(map);
System.out.println("map的key进行倒序正序排序 = " + keyAsc);

Map<String, Area> keyDesc = Java8MapUtil.sortByKeyDesc(map);
System.out.println("map的key进行倒序排序 = " + keyDesc);

Map<String, Double> valueAsc = Java8MapUtil.sortByValueAsc(singleMap);
System.out.println("map的value进行倒序正序排序 = " + valueAsc);

Map<String, Double> valueDesc = Java8MapUtil.sortByValueDesc(singleMap);
System.out.println("map的value进行倒序排序 = " + valueDesc);


// 集合对象转Map
Map<Integer, Area> areaMap = valueList.stream().collect(toMap(Area::getId, Function.identity(), (existing, replacement) -> existing));
System.out.println("集合对象转Map = " + areaMap);

// List转ConcurrentMap
ConcurrentHashMap<Integer, Area> concurrentHashMap = valueList.stream().collect(toMap(Area::getId, Function.identity(), (o1, o2) -> o1, ConcurrentHashMap::new));
System.out.println("List转ConcurrentMap = " + concurrentHashMap);

// 根据集合对象某一个值排序后分组转化为TreeMap
Map<Integer, Area> treeMap = valueList.stream().sorted(Comparator.comparing(Area::getId)).collect(toMap(Area::getId, Function.identity(), (o1, o2) -> o1, TreeMap::new));
System.out.println("根据集合对象某一个值排序后分组转化为TreeMap = " + treeMap);

@Test
public void listMapGroupBy() {
    List<Map<String, Object>> list = new ArrayList<>();
    Map<String, Object> paramMap = new HashMap<>();

    paramMap = new HashMap<>();
    paramMap.put("dicId", 2);
    paramMap.put("dicName", "钢筋");
    paramMap.put("dicDes", "钢筋1号");
    list.add(paramMap);

    paramMap.put("dicId", 1);
    paramMap.put("dicName", "钢材");
    paramMap.put("dicDes", "钢材1号");
    list.add(paramMap);

    paramMap = new HashMap<>();
    paramMap.put("dicId", 3);
    paramMap.put("dicName", "钢筋");
    paramMap.put("dicDes", "钢筋2号");
    list.add(paramMap);

    paramMap = new HashMap<>();
    paramMap.put("dicId", 3);
    paramMap.put("dicName", "河沙");
    paramMap.put("dicDes", "河沙1号");
    list.add(paramMap);

    Map<String, List<Map<String, Object>>> mapGroup = list.stream().collect(groupingBy(map -> map.get("dicId").toString()));
    System.out.println("mapGroup = " + mapGroup);
}

Map<String, Object> map = JSONObject.parseObject(jsonData, new TypeReference<Map<String, Object>>() {
});

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