Java 8 Lsit和Map之间转化-代码示例

1、List<T>转Map<S,List<T>>

Map<String, List<Entity>> demoMap = demoList.stream()
.collect(Collectors.groupingBy(Entity::getkey)); // the type of demoList is List<Entity>
Entity实例getkey()方法返回的值则作为map的key，即按该字段给demoList分类。

2、Map<S,List<T>>转List<T>

List<Entity> demoList = refDataMap.entrySet().stream()
.flatMap(map -> map.getValue().stream())
.collect(Collectors.toList()); //the type of refDataMap is Map<S,List<Entity>>3、List<T>转Map<S,T>
Map<String,Entity> map = stats.stream().collect(Collectors.toMap(Entity::getKey,
c -> c));
Map<String,String> map = stats.stream().collect(Collectors.toMap(Entity::getKey,
Entity::getStringValue)); //the type of stats if List<Entity>

------未完待续---------