JDK1.8新特性應用 ——List＜Map＜String,Object＞＞

使用stream對指定List<Map<String,Object>>進行排序

//map的value值轉化為List<Map<String, Object>>形式
List<Map<String, Object>> result = new ArrayList<Map<String,Object>>(forcaseResulMap.values());

//對list根據里面的map結構的key為time的字段進行排序
result=result.stream().sorted((map1,map2)->{
				return map1.get("time").toString().compareTo(map2.get("time").toString());
		}).collect(Collectors.toList());

 

根據map中的score進行過濾

List<Map<String,Object>> list = Lists.newArrayList();
IntStream.range(1,5).forEach(e->{
    Map<String,Object> map = Maps.newHashMap();
    map.put("name","張三"+(e<3?e:e-1));
    map.put("score", (int)(Math.random()*100)+1);
    list.add(map);
});
System.out.println(list);

//過濾分數大於60的元素
List<Map<String, Object>> filterList = list.stream().filter(
    e -> (int) e.get("score") > 60).collect(Collectors.toList());
System.out.println(filterList);

 

對集合中的map的value值求和

List<Map<String,Object>> list = Lists.newArrayList();
IntStream.range(1,5).forEach(e->{
    Map<String,Object> map = Maps.newHashMap();
    map.put("name","張三"+(e<3?e:e-1));
    map.put("score", (int)(Math.random()*100)+1);
    list.add(map);
});
System.out.println(list);

//通過Collect方式
int score = list.stream().collect(Collectors.summingInt(
    e -> Integer.parseInt(e.get("score").toString())));
//通過map方式
int sum = list.stream().mapToInt(e -> Integer.parseInt(e.get("score").toString())).sum();
System.out.println(sum);

 

根據map的name進行分組，並將name相同的score值求和

List<Map<String,Object>> list = Lists.newArrayList();
IntStream.range(1,5).forEach(e->{
    Map<String,Object> map = Maps.newHashMap();
    map.put("name","張三"+(e<3?e:e-1));
    map.put("score", (int)(Math.random()*100)+1);
    list.add(map);
});
System.out.println(list);


List<Map<String, Object>> collectList = list.stream().collect(
    Collectors.groupingBy(e -> e.get("name"))).values().stream().map(e -> {
    Map<String, Object> map = e.get(0);
    map.put("score", e.stream().map(
        s -> new BigInteger(s.get("score").toString())).reduce(BigInteger.ZERO, BigInteger::add));
    return map;
}).collect(Collectors.toList());
System.out.println(collectList);

 

Java8 stream 對List<Map<String,Object>> 去重

//構建數據
List<Map<String,Object>> list1 = new ArrayList<>();
     
Map<String,Object> map = new HashMap();
Map<String,Object> map2 = new HashMap();

map.put("key","1");
map.put("value","a");
map2.put("key","2");
map2.put("value","a");

list1.add(map2);
list1.add(map);
	       
list1.forEach(System.out::println);   //打印數據

List<Map<String, Object>> list2 = list1.stream().collect(
	               Collectors.collectingAndThen(
	                       Collectors.toCollection(
	                       () ->new TreeSet<>(Comparator.comparing(m->m.get("value").toString()))
	                       ),ArrayList::new
	               )
	       );    //根據value字段值去重，保留第一次放入list的map值
System.out.println("--------");
list2.forEach(System.out::println);

//結果打印：
//{value=a, key=2}
//{value=a, key=1}
//--------
//{value=a, key=2}

 

Java8 stream 更改List<Map<String,Object>> 里面Map對象的值

//構建對象
List<Map<String, Object>> list1 = new ArrayList<>();

Map<String, Object> map = new HashMap();
Map<String, Object> map2 = new HashMap();

map.put("key", "1");
map.put("value", "a");
map2.put("key", "2");
map2.put("value", "a");

list1.add(map2);
list1.add(map);

list1.forEach(System.out::println);

//將Map里面的每一個對象的key改為aaaa
List<Map<String, Object>> list2 = list1.stream().map(x -> {
			x.put("key", "aaaa");
			return x;
		}).collect(Collectors.toList());
System.out.println("--------");
list2.forEach(System.out::println);		


//{value=a, key=2}
//{value=a, key=1}
//--------
//{value=a, key=aaaa}
//{value=a, key=aaaa}

 

 

 

轉載：https://www.cnblogs.com/zklymm/p/13986205.html