java中lamda表达式用法

map-> list

        Map map = new HashMap<>();
        List list = new ArrayList<>();
        map.forEach((k, v) -> {
            list.add(v.toString());
        });

list->map

@Data
public class TestEntity {
  private String code;
  private String name;    
}

        List list = new ArrayList<>();
        Map map = list.stream().collect(
          Collectors.toMap(item -> ((TestEntity )item).getCode,
                  item -> (TestEntity)item)
        );