java.lang.ClassCastException：[Ljava.lang.Object；无法强制转换或 BeanUtils.copyProperties 不起作用

Question

我是 JPA 新手，使用 @Query 参数时 springboot 无法获得 api 响应（我尝试实现内部连接）

存储库类：

 @Transactional(rollbackFor = Exception.class)
    @Modifying
    @Query("select A.id, A.position ,A.title,A.shortdescription,A.thumbnailimage, A.linkactions, A.last_updated_date, A.last_updated_by, B.countryName " +
            "from ContentManage as A inner join Country as B on A.countryid=B.countryId")
    List<ContentManage> fetchDataInnerJoin();

服务类：

public ContentManageListResponse queryAllActions() {
        List<ContentManage> contentManageList = contentManageRepository.fetchDataInnerJoin();
        List<ContentManageVO> contentManageVOList = new ArrayList<>();
        for (ContentManage contentManage : contentManageList) {
            ContentManageVO contentManageVO = new ContentManageVO();
            BeanUtils.copyProperties(contentManage,contentManageVO);
            contentManageVOList.add(contentManageVO);
        }
        return ContentManageListResponse.builder().contents(contentManageVOList).build();
    }

我得到了“[Ljava.lang.Object; cannot be cast”异常，之后我改为如下：

服务等级

public ContentManageListResponse queryAllActions() {
        List<ContentManage> contentManageList = contentManageRepository.fetchDataInnerJoin();
        List<ContentManageVO> contentManageVOList = new ArrayList<>();
        for (Object contentManage : contentManageList) {
            ContentManageVO contentManageVO = new ContentManageVO();
            BeanUtils.copyProperties(contentManage,contentManageVO);
            contentManageVOList.add(contentManageVO);
        }
        return ContentManageListResponse.builder().contents(contentManageVOList).build();
    }

foreach 添加了对象，但是对于上面的代码，我得到了空值 BeanUtils.copyProperties 不起作用

请任何人建议如何解决此问题。

Answer 1

你的陈述

@Query("select A.id, A.position ,A.title,A.shortdescription,A.thumbnailimage, A.linkactions, A.last_updated_date, A.last_updated_by, B.countryName " +
            "from ContentManage as A inner join Country as B on A.countryid=B.countryId")

在选择中包含来自ContentManage 和Country 的部分。 但你的结果只是一个List<ContentManage>

要解决这个问题，您可以创建一个新的 Dto 类，其中包含您需要的 A 和 B 的所有字段。这个 Dto 类必须有一个全参数的构造函数。然后代替

 "select A.id, A.position ,A.title,A.shortdescription,A.thumbnailimage, A.linkactions, A.last_updated_date, A.last_updated_by, B.countryName " +
            "from ContentManage as A inner join Country as B on A.countryid=B.countryId"

你可以写：

"select new com.you.package.YourDtoClass (A.id, A.position ,A.title,A.shortdescription,A.thumbnailimage, A.linkactions, A.last_updated_date, A.last_updated_by, B.countryName) " +
            "from ContentManage as A inner join Country as B on A.countryid=B.countryId"

Answer 2

Controller.java
===============

@Autowired
    private Service Service;
    
@ApiHeader(
            apiOperation = "get all Content Manage",
            apiOperationNotes = "get all Content Manage"
    )
    @GetMapping(value = UriConstants.CONTENT_MANAGE_QUERY,produces = {MediaType.APPLICATION_JSON_VALUE})

    public ResponseEntity<CMListResponse> queryAllCM(
            @RequestHeader HttpHeaders apiRequest){
        CMListResponse response = CMService.queryAllCM();
        return ResponseEntity.ok(response);
    }
    

CMListResponse.java
==============================
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class CMListResponse {
    List<CMVO> contents;
}

CMVO.java
=====================
@Setter
@Getter
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class CMVO {

    private static final long serialVersionUID = 92012330342289044L;

    @ApiModelProperty(value = "id", example = "123")
    @JsonProperty(value = "id")
    private int id;

    @ApiModelProperty(value = "position", example = "123")
    @JsonProperty(value = "position")
    private int position;

    @ApiModelProperty(value = "title", example = "desc")
    @JsonProperty(value = "title")
    private String title;

    @ApiModelProperty(value = "shortDescription", example = "shortDescription")
    @JsonProperty(value = "shortDescription")
    private String shortdescription;

    @ApiModelProperty(value = "thumbnailimage", example = "thumbnailimage")
    @JsonProperty(value = "thumbnailimage")
    private String thumbnailimage;

    @ApiModelProperty(value = "linkactions", example = "linkactions")
    @JsonProperty(value = "linkactions")
    private String linkactions;

    /*@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd")*/
    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ss.SSSX")
    @ApiModelProperty(value = "last_updated_date", example = "2021-03-17T02:59:24.120Z")
    @JsonProperty(value = "last_updated_date")
    private ZonedDateTime last_updated_date;

    @ApiModelProperty(value = "last_updated_by", example = "A9002255")
    @JsonProperty(value = "last_updated_by")
    private String last_updated_by;

    @ApiModelProperty(value = "countryid", example = "3023D08B-D861-4514-8E13-FFCF97A3D1DD")
    @JsonProperty(value = "countryid")
    private String countryid;

    @ApiModelProperty(value = "countryName", example = "Singapore")
    @JsonProperty(value = "countryName")
    private String countryName;

    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd'T'HH:mm:ss.SSSX")
    @ApiModelProperty(value = "date_published", example = "2021-03-17T02:59:24.120Z")
    @JsonProperty(value = "date_published")
    private ZonedDateTime date_published;

    @Override
    public String toString() {
        return "CMVO{" +
                "id=" + id +
                ", position=" + position +
                ", title='" + title + '\'' +
                ", shortdescription='" + shortdescription + '\'' +
                ", thumbnailimage='" + thumbnailimage + '\'' +
                ", linkactions='" + linkactions + '\'' +
                ", last_updated_date=" + last_updated_date +
                ", last_updated_by='" + last_updated_by + '\'' +
                ", countryid='" + countryid + '\'' +
                ", countryName='" + countryName + '\'' +
                ", date_published=" + date_published +
                '}';
    }
}

service.java
=============
 private Repository repository;

    @Autowired
    public CMService(Repository Repository) {
        this.Repository = Repository;
    }
 public CMListResponse queryAllCM() {
        List<CCDTO> CMList =
                Repository.fetchAllCMData();
        List<CMVO> CMVOList = new ArrayList<>();
        for (CCDTO CM : CMList) {
            CMVO CMVO = new CMVO();
            BeanUtils.copyProperties(CM,CMVO);
            CMVOList.add(CMVO);
        }
        return CMListResponse.builder().contents(CMVOList).build();
    }
    
    
CCDTO.java
==========
@Setter
@Getter
@Builder
@AllArgsConstructor
public class CCDTO {

    private  int id;
    private  int position;
    private  String title;
    private  String shortdescription;
    private  String thumbnailimage;
    private  String linkactions;
    private  ZonedDateTime last_updated_date;
    private  String last_updated_by;
    private  String countryid;
    private  String countryName;
    private  ZonedDateTime date_published;



    @Override
    public String toString() {
        return "CCDTO{" +
                "id=" + id +
                ", position=" + position +
                ", title='" + title + '\'' +
                ", shortdescription='" + shortdescription + '\'' +
                ", thumbnailimage='" + thumbnailimage + '\'' +
                ", linkactions='" + linkactions + '\'' +
                ", last_updated_date=" + last_updated_date +
                ", last_updated_by='" + last_updated_by + '\'' +
                ", countryid='" + countryid + '\'' +
                ", countryName='" + countryName + '\'' +
                ", date_published=" + date_published +
                '}';
    }
}

repository.java
===============
@Transactional(rollbackFor = Exception.class)
    @Query("select new com.model.entity.CCDTO (A.id, A.position ,A.title," +
            "A.shortdescription,A.thumbnailimage, A.linkactions, A.last_updated_date, A.last_updated_by, " +
            "A.country.countryId, A.country.countryName, A.date_published) " +
            "from CM as A inner join A.country as B order by A.id asc")
    List<CCDTO> fetchAllCMData();