Java 通过List<String>对Map<String, String>中key和value分区分组的方法及示例代码

1､使用partitioningBy和toMap实现

Map<String, String> myMap = new HashMap<>();
myMap.put("d", "D");
myMap.put("c", "C");
myMap.put("b", "B");
myMap.put("A", "A");
List<String> myList = Arrays.asList("a", "b", "c");
Map<Boolean, Map<String, String>> result = myMap.entrySet()
        .stream()
        .collect(Collectors.partitioningBy(
                            entry -> myList.contains(entry.getKey()),
                            Collectors.toMap(Entry::getKey, Entry::getValue)
                    )
        );

结果：

{false={A=A, d=D}, true={b=B, c=C}}

2､使用forEach实现

Map<String, String> myMap = new HashMap<>();
myMap.put("d", "D");
myMap.put("c", "C");
myMap.put("b", "B");
myMap.put("A", "A");
List<String> list = Arrays.asList("a", "b", "c");
Map<Boolean, Map<String, String>> result = Map.of(true, new LinkedHashMap<>(), 
                                                  false, new LinkedHashMap<>());
Set<String> set = new HashSet<>(list);
myMap.forEach((k, v) -> result.get(set.contains(k)).put(k, v));

结果：

{false={A=A, d=D}, true={b=B, c=C}}

3､使用for实现

Map<String, String> myMap = new HashMap<>();
myMap.put("d", "D");
myMap.put("c", "C");
myMap.put("b", "B");
myMap.put("A", "A");
List<String> list = Arrays.asList("a", "b", "c");
Map<String, String> contains = new HashMap<>();
Map<String, String> containsNot = new HashMap<>();
for(Map.Entry<String, String> entry :  myMap.entrySet()) {
    if (list.contains(entry.getKey())) {
        contains.put(entry.getKey(), entry.getValue());
    } else {
        containsNot.put(entry.getKey(), entry.getValue());
    }
}

结果：

{false={A=A, d=D}, true={b=B, c=C}}

4､使用groupingBy实现

Map<String, String> myMap = new HashMap<>();
myMap.put("d", "D");
myMap.put("c", "C");
myMap.put("b", "B");
myMap.put("A", "A");
List<String> myList = Arrays.asList("a", "b", "c");
Function<Entry<String, String> , Boolean> myCondition =  i -> myList.contains(i.getKey());
Map<Boolean,List<Entry<String, String>>>  myPartedMap = myMap.entrySet()
        .stream().collect(Collectors.groupingBy(myCondition));
System.out.println(myPartedMap);

结果：

{false={A=A, d=D}, true={b=B, c=C}}

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