Java 流 - 编译时错误 - 类型不匹配：无法从 Map<Object,Object> 转换为 Map<Integer,List<String>>

Question

我有一个简单的代码，我将我的自定义 class 对象列表转换为 Map>。 代码如下：

List<NPDto> appList = new ArrayList<NPDto>(); 
//list gets populated though some other method

//Here is conerting code where i get compile time error
final Map<Integer, List<String>> appMap = appList.stream()
                                              .collect(
                                                Collectors.toMap(
                                                  np -> NumberUtils.toInt(np.getPId()),
                                                  np -> Arrays.asList(np.getAppsReceived().split(","))
                                              ));
// Here is my DTO                                              
public class NPDto {

    private String pId;
  private String appsReceived;

  public String getPId(){
    return pId;
  }

  public void setPId(String pId){
    this.pId = pId;
  }

  public String getAppsReceived(){
    return appsReceived;
  }

  public void setAppsReceived(String appsReceived){
    this.appsReceived = appsReceived;
  }
}

但是，我收到如下编译器错误：

Type mismatch: cannot convert from Map<Object,Object> to Map<Integer,List<String>>

I am compiling with Java SE 8[1.8.0_91]

不知道我哪里错了。有人可以帮忙吗？

Answer 1

你需要做一些小改动，因为 split returns a String [].

np -> Arrays.asList(np.getAppsReceived().split(","))