Java 中对象List 转map实践

class MyObject {     Long id;     String name;      // Constructor     public MyObject(Long id, String name) {         this.id = id;         this.name = name;     }      // Getters     public Long getId() {         return id;     }      public String getName() {         return name;     } } 

第一种 List 转 Map<Long, String>

List<MyObject> myObjectList=new ArrayList<>(); //  自行赋值   Map<Long, String> map = myObjectList.stream()  					.collect(Collectors.toMap(                             MyObject::getId,   // key mapper                             MyObject::getName// value mapper                     )); 

第二种 List 转 Map<Long, List>

List<MyObject> myObjectList=new ArrayList<>(); //  自行赋值   Map<Long, List<String>>  map = myObjectList.stream()                         .collect(Collectors.groupingBy(                                 MyObject::getId, // key mapper                                 Collectors.mapping(MyObject::getName, Collectors.toList()) // value mapper                         ));