使用java8 新特性stream流对List＜Map＜String, Object＞＞集合进行遍历、过滤、查询、去重、排序、分组

对于一个List<Map<String, Object>>类型的数据，可以使用Java 8的新特性stream流来进行遍历、过滤、查询、去重、排序、分组等操作。

遍历：

List<Map<String, Object>> dataList = new ArrayList<Map<String, Object>>();

//添加数据
Map<String, Object> map1 = new HashMap<String, Object>();
map1.put("id", 1);
map1.put("name", "张三");
dataList.add(map1);

Map<String, Object> map2 = new HashMap<String, Object>();
map2.put("id", 2);
map2.put("name", "李四");
dataList.add(map2);

//使用stream流进行遍历
dataList.stream().forEach(map -> {
    System.out.println("id：" + map.get("id") + "，name：" + map.get("name"));
});

过滤：

List<Map<String, Object>> dataList = new ArrayList<Map<String, Object>>();

//添加数据
Map<String, Object> map1 = new HashMap<String, Object>();
map1.put("id", 1);
map1.put("name", "张三");
map1.put("age", 20);
dataList.add(map1);

Map<String, Object> map2 = new HashMap<String, Object>();
map2.put("id", 2);
map2.put("name", "李四");
map2.put("age", 30);
dataList.add(map2);

//使用stream流进行过滤
dataList.stream().filter(map -> (Integer) map.get("age") > 25).forEach(map -> {
    System.out.println("id：" + map.get("id") + "，name：" + map.get("name"));
});

查询：

List<Map<String, Object>> dataList = new ArrayList<Map<String, Object>>();

//添加数据
Map<String, Object> map1 = new HashMap<String, Object>();
map1.put("id", 1);
map1.put("name", "张三");
map1.put("age", 20);
dataList.add(map1);

Map<String, Object> map2 = new HashMap<String, Object>();
map2.put("id", 2);
map2.put("name", "李四");
map2.put("age", 30);
dataList.add(map2);

//使用stream流进行查询
Optional<Map<String, Object>> optionalMap = dataList.stream().filter(map -> (Integer) map.get("id") == 1).findFirst();
if (optionalMap.isPresent()) {
    Map<String, Object> map = optionalMap.get();
    System.out.println("id：" + map.get("id") + "，name：" + map.get("name") + "，age：" + map.get("age"));
}

去重：

List<Map<String, Object>> dataList = new ArrayList<Map<String, Object>>();

//添加数据
Map<String, Object> map1 = new HashMap<String, Object>();
map1.put("id", 1);
map1.put("name", "张三");
map1.put("age", 20);
dataList.add(map1);

Map<String, Object> map2 = new HashMap<String, Object>();
map2.put("id", 2);
map2.put("name", "李四");
map2.put("age", 30);
dataList.add(map2);

Map<String, Object> map3 = new HashMap<String, Object>();
map3.put("id", 2);
map3.put("name", "李四");
map3.put("age", 30);
dataList.add(map3);

//使用stream流进行去重
List<Map<String, Object>> distinctList = dataList.stream().distinct().collect(Collectors.toList());
distinctList.stream().forEach(map -> {
    System.out.println("id：" + map.get("id") + "，name：" + map.get("name") + "，age：" + map.get("age"));
});

排序：

List<Map<String, Object>> dataList = new ArrayList<Map<String, Object>>();

//添加数据
Map<String, Object> map1 = new HashMap<String, Object>();
map1.put("id", 1);
map1.put("name", "张三");
map1.put("age", 20);
dataList.add(map1);

Map<String, Object> map2 = new HashMap<String, Object>();
map2.put("id", 2);
map2.put("name", "李四");
map2.put("age", 30);
dataList.add(map2);

Map<String, Object> map3 = new HashMap<String, Object>();
map3.put("id", 3);
map3.put("name", "王五");
map3.put("age", 25);
dataList.add(map3);

//使用stream流进行排序
List<Map<String, Object>> sortedList = dataList.stream().sorted((map1, map2) -> (Integer) map1.get("age") - (Integer) map2.get("age")).collect(Collectors.toList());
sortedList.stream().forEach(map -> {
    System.out.println("id：" + map.get("id") + "，name：" + map.get("name") + "，age：" + map.get("age"));
});

分组：文章来源地址https://www.toymoban.com/news/detail-688573.html

List<Map<String, Object>> dataList = new ArrayList<Map<String, Object>>();

//添加数据
Map<String, Object> map1 = new HashMap<String, Object>();
map1.put("id", 1);
map1.put("name", "张三");
map1.put("age", 20);
dataList.add(map1);

Map<String, Object> map2 = new HashMap<String, Object>();
map2.put("id", 2);
map2.put("name", "李四");
map2.put("age", 30);
dataList.add(map2);

Map<String, Object> map3 = new HashMap<String, Object>();
map3.put("id", 3);
map3.put("name", "王五");
map3.put("age", 25);
dataList.add(map3);

//使用stream流进行分组
Map<Integer, List<Map<String, Object>>> groupMap = dataList.stream().collect(Collectors.groupingBy(map -> (Integer) map.get("age")));
for (Map.Entry<Integer, List<Map<String, Object>>> entry : groupMap.entrySet()) {
    Integer age = entry.getKey();
    List<Map<String, Object>> list = entry.getValue();
    System.out.println("年龄为" + age + "的人数为" + list.size());
}

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