Java Stream - 编译时错误 - 类型与 Map<Integer,List<String>> 不匹配 : cannot convert from Map<Object, Object>

Question

我有一个简单的代码，我将自定义类对象的列表转换为 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]

不知道哪里错了。有人可以帮忙吗？

Answer 1

您需要稍作更改，因为 split 返回一个 String []。

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