在包含 blob 的响应中发送实体对象

Question

我正在尝试创建一个 springboot 用户管理应用程序。

我有一个实体对象，其中包含两个 blob elements.Here 是我的实体对象。

 @Entity
    @Table(name="user_meta_profile")
    public class UserMetaProfile implements Serializable {
        private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "user_id")
    private int user_id;

    @Column(name = "resume_file")
    @Lob
    private Blob resume_file;

    @Column(name = "photo")
    @Lob
    private Blob photo;

    @Column(name = "username")
    private String username;

    public int getUser_id() {
        return user_id;
    }

    public void setUser_id(int user_id) {
        this.user_id = user_id;
    }

    public Blob getResume_file() {
        return resume_file;
    }

    public void setResume_file(Blob resume_file) {
        this.resume_file = resume_file;
    }

    public Blob getPhoto() {
        return photo;
    }

    public void setPhoto(Blob photo) {
        this.photo = photo;
    }

   public void setUsername(String username) {
        this.username = username;
    }
}

如您所见，有两个 blob 项 'resume_file' 和 'photo'。

我想发回对 API 调用的 JSON 响应。

我的控制器代码如下图

 @Controller
    @RequestMapping("/v1")
    public class UsersController {

    @Autowired 
        private IUserMetaProfileService userMetaProfileService;


    @GetMapping("MetaProfile/{id}")
        public ResponseEntity<UserMetaProfile> getUserMetaProfileById(@PathVariable("id") Integer id) {
            UserMetaProfile userMetaProfile = userMetaProfileService.getUsersById(id);
            return new ResponseEntity<UserMetaProfile>(userMetaProfile, HttpStatus.OK);
        }

    }

但是当我调用 API 时，出现异常：

"exception": "org.springframework.http.converter.HttpMessageNotWritableException",

 "message": "Could not write JSON document: No serializer found for class java.io.ByteArrayInputStream and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain:
...

   ...nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class java.io.ByteArrayInputStream and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS)

Answer 1

由于 JSON 不能包含二进制数据，您需要将这些字段序列化为其他内容。您有几个选择：

如果您打算将二进制文件显示为图像（因为您的是照片），您可以将其序列化为数据 uri。
改为发送照片链接并创建一个控制器方法，该方法将输出具有适当内容类型的二进制数据（超出此处的范围）。

所以对于选项 1，您可以这样做：

@Entity
@Table(name="user_meta_profile")
public class UserMetaProfile implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "user_id")
    private int user_id;

    @Column(name = "resume_file")
    @Lob
    private Blob resume_file;

    @Column(name = "photo")
    @Lob
    private Blob photo;

    @Column(name = "username")
    private String username;

    public int getUser_id() {
        return user_id;
    }

    public void setUser_id(int user_id) {
        this.user_id = user_id;
    }

    @JsonIgnore // disable serializing this field by default
    public Blob getResume_file() {
        return resume_file;
    }

    // serialize as data uri insted
    @JsonProperty("resumeData")
    public String getResume() {
      // just assuming it is a word document. you would need to cater for different media types
      return "data:application/vnd.openxmlformats-officedocument.wordprocessingml.document;base64," + new String(Base64.getEncoder().encode(resume_file.getBytes()));
    }

    public void setResume_file(Blob resume_file) {
        this.resume_file = resume_file;
    }

    @JsonIgnore // disable this one too
    public Blob getPhoto() {
        return photo;
    }

    // serialize as data uri instead
    @JsonProperty("photoData")
    public String getPhotoBase64() {
      // just assuming it is a jpeg. you would need to cater for different media types
      return "data:image/jpeg;base64," + new String(Base64.getEncoder().encode(photo.getBytes()));
    }

    public void setPhoto(Blob photo) {
        this.photo = photo;
    }

   public void setUsername(String username) {
        this.username = username;
    }
}

对于照片位，photoData JSON 属性的值可以直接设置为 img 标签的 src 属性，照片将被渲染在 HTML。使用简历文件，您可以将其作为 href 附加到具有 download 属性的 <a> 标签，以便下载：

<a href={photoData value here} download>Download Resume File</a>

仅供参考，如果文件很大，JSON 会很大，而且还可能会降低浏览器速度。

在包含 blob 的响应中发送实体对象

Sending Entity Object in Response which contains blob

java

json

blob

httpresponse

spring-boot