Spring Boot - 使用自定义对象数组的 JSON 序列化自定义对象答案

【问题标题】：Spring Boot - JSON Serialize Custom Object with Array of Custom ObjectsSpring Boot - 使用自定义对象数组的 JSON 序列化自定义对象
【发布时间】：2017-12-02 10:33:10
【问题描述】：

有这个类：

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private int key;
private String text;
private Tag[] tags;
private String title;
private boolean valid;
public Activity(int key, String text, Tag[] tags, String title) {
    this.key = key;
    this.text = text;
    this.tags = tags;
    this.title = title;
    valid = true;
}

它有一个与之关联的Tag 数组。标签如下所示：

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private long id;
private long activityId;
private String keyword;

public Tag(String keyword){
    this.keyword = keyword;
    activityId = -1;
}

Activity 和 Tag 都是实体，并且都有存储库：

public interface TagRepository extends CrudRepository<Tag, Long> {

}

public interface ActivityRepository extends CrudRepository<Activity, Long> {

}

有这个 create - 方法在数据库中存储了一个 Activity 对象：

  @PostMapping
  public Activity create(@RequestBody Activity input) {
      if(input.getTags() != null) {
          for(Tag t : input.getTags()) {
              t.setActivityId(input.getId()); //associate which activity has which tags
              tagRepository.save(t);
          }
      }

      return activityRepository.save(input);
  }

我通过 POST 传输这个 JSON：

{
    "key":2,
    "text":"Hello",
    "tags":[{
        "keyword":"h"
    },{
        "keyword":"b"
    }
    ],
    "title":"world"
}

但我收到此错误：

"status": 500,
"error": "Internal Server Error",
"exception": "org.springframework.orm.jpa.JpaSystemException",
"message": "could not serialize; nested exception is org.hibernate.type.SerializationException: could not serialize"

两个类都有每个成员变量的 getter/setter，并且都有默认的 ctors，我只是没有在此处显示它们以使问题尽可能简短。

【问题讨论】：

用@OneToMany 注释标签属性？
我得到：org.hibernate.AnnotationException: List/array has to be annotated with an @OrderColumn (or @IndexColumn): base.Activity.tags

标签： java json spring hibernate jpa

【解决方案1】：

首先，您需要在活动和标签之间建立关系。 Activity有很多标签，那么关系应该是oneToMany。

http://www.baeldung.com/hibernate-one-to-many

@Entity
@Table(name="ACTIVITY")
public class Activity {
  @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
  private long id;
  private int key;
  private String text;

  @OneToMany(mappedBy="activity")
  private List<Tag> tags;

  private String title;
  private boolean valid;
  public Activity(int key, String text, List<Tag> tags, String title) {
    this.key = key;
    this.text = text;
    this.tags = tags;
    this.title = title;
    valid = true;
  }
}

@Entity
@Table(name="TAG")
public class Tag {
  @Id
  @GeneratedValue(strategy=GenerationType.AUTO)
  private long id;

  @ManyToOne
  @JoinColumn(name="activity_id", nullable=false)
  private Activity activity;

  private String keyword;

  public Tag(String keyword){
    this.keyword = keyword;
    activityId = -1;
  }
}

首先，您没有使用 CASCADE.ALL 属性，这意味着您将手动处理标签实体的保存。

@PostMapping
  public Activity create(@RequestBody Activity input) {
      if(input.getTags() != null) {
          //you are saving all the nested tags manually before saving the activity
          for(Tag t : input.getTags()) {
              tagRepository.save(t);
          }
      }
      //now you are saving activity which contains these tags
      return activityRepository.save(input);
  }

【讨论】：