List转Map

方法：

public class ListToMapTest {

    public Map listToMap(List<User> list) {
        Map<Integer, User> map = new HashMap<>();
        for (User user : list) {
            map = list.stream().collect(Collectors.toMap(it -> it.getId(), it -> it));
        }
        return map;
    }
}

测试：

ListToMapTest listToMapTest = new ListToMapTest();
ArrayList<User> users = new ArrayList<>();
User user1 = new User(1, "k1", 11);
User user2 = new User(2, "k2", 12);
users.add(user1);
users.add(user2);
Map map = listToMapTest.listToMap(users);
System.out.println(map.toString());

结果：

{1=User{id=1, name='k1', age=11}, 2=User{id=2, name='k2', age=12}}