使用GSON解析JSON至JPA持久化模型时遇异常，求解决方案

问题场景 #

需要解析外部API返回的JSON数据，通过JPA注解持久化到数据库，使用GSON作为解析器并自定义TypeAdapter，当前代码运行抛出UnsupportedOperationException: JsonObject异常，相关代码如下：

测试JSON（test.json） #

{"workID": 12355,"contributors":[{"fullName": "UNKNOWN 1","workContributorID": 1100933315,"workID": 12355},{"fullName": "UNKNOWN 2","workContributorID": 1100933314,"workID": 12355}]}

原JPA实体类 #

Contributor.java

import jakarta.persistence.*;
import lombok.Getter;
import lombok.Setter;

@Getter
@Setter
@Entity
@Table(name = "contributor")
public class Contributor {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private long workContributorID;

    private String fullName;

    @ManyToOne
    @JoinColumn(name = "work_id", referencedColumnName = "id")
    private WorkSP workID;
}

WorkSP.java

import jakarta.persistence.*;
import lombok.Getter;
import lombok.Setter;

import java.util.ArrayList;

@Getter
@Setter
@Entity
@Table(name = "work_sp")
public class WorkSP {
    @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private long workID;
    private ArrayList<Contributor> contributors;


    public WorkSP(long asLong) {
        this.workID = asLong;
    }
}

原测试类（App.java） #

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializer;
import com.google.gson.stream.JsonReader;

import java.io.FileNotFoundException;
import java.io.FileReader;

public class App 
{
    public static void main( String[] args ) throws FileNotFoundException {
        JsonReader readerTest = new JsonReader(new FileReader("test.json"));
        Gson gSonInstance = new GsonBuilder().
                registerTypeAdapter(WorkSP.class, (JsonDeserializer<WorkSP>) (json, type, jsonDeserializationContext) -> {
                return new WorkSP(json.getAsJsonObject().getAsLong());
                }).
                create();
        WorkSP work = gSonInstance.fromJson(readerTest, WorkSP.class);
    }
}

抛出的异常 #

Exception in thread "main" java.lang.UnsupportedOperationException: JsonObject
    at com.google.gson.JsonElement.getAsLong(JsonElement.java:294)
    at org.example.App.lambda$main$0(App.java:21)
    at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:95)
    at com.google.gson.Gson.fromJson(Gson.java:1361)
    at com.google.gson.Gson.fromJson(Gson.java:1306)
    at org.example.App.main(App.java:24)

错误原因 #

1. WorkSP反序列化逻辑错误：自定义反序列化器中调用json.getAsJsonObject().getAsLong()，但getAsJsonObject()返回的是包含workID和contributors的完整JSON对象，直接对JsonObject调用getAsLong()会触发类型不匹配异常。
2. 实体类缺少无参构造：GSON和JPA都要求实体类必须有公共无参构造函数，原WorkSP类只有带参构造，会导致GSON无法实例化对象。
3. JPA关联关系注解不完整：WorkSP与Contributor是一对多关系，原代码未添加@OneToMany注解及关联配置，持久化时会出现关联异常。
4. Contributor的workID字段解析问题：JSON中Contributor的workID是long值，但实体类中是WorkSP类型，GSON无法自动完成类型转换，需要自定义反序列化逻辑。

修复方案 #

1. 修正JPA实体类 #

调整WorkSP.java

import jakarta.persistence.*;
import lombok.Getter;
import lombok.Setter;
import java.util.List;

@Getter
@Setter
@Entity
@Table(name = "work_sp")
public class WorkSP {
    @Id
    // 若JSON中的workID是业务主键，不需要数据库自增则删除@GeneratedValue
    // @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private long workID;

    // 配置一对多关联，cascade确保级联操作，mappedBy对应Contributor中的关联字段
    @OneToMany(mappedBy = "workID", cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Contributor> contributors;

    // 添加GSON和JPA必需的无参构造
    public WorkSP() {}

    public WorkSP(long workID) {
        this.workID = workID;
    }
}

调整Contributor.java

import jakarta.persistence.*;
import lombok.Getter;
import lombok.Setter;
import com.google.gson.annotations.JsonDeserialize;

@Getter
@Setter
@Entity
@Table(name = "contributor")
public class Contributor {
    @Id
    // 若workContributorID是业务主键，删除@GeneratedValue
    // @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private long workContributorID;

    private String fullName;

    @ManyToOne
    @JoinColumn(name = "work_id", referencedColumnName = "id")
    // 指定自定义反序列化器，将long值转为WorkSP对象
    @JsonDeserialize(using = WorkSPDeserializer.class)
    private WorkSP workID;
}

2. 编写Contributor的workID反序列化器 #

创建WorkSPDeserializer.java，处理JSON中long类型的workID到WorkSP对象的转换：

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import java.lang.reflect.Type;

public class WorkSPDeserializer implements JsonDeserializer<WorkSP> {
    @Override
    public WorkSP deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        // 从JSON中取出long类型的workID，创建对应的WorkSP对象
        long workId = json.getAsLong();
        return new WorkSP(workId);
    }
}

3. 修正测试类的GSON反序列化逻辑 #

修改App.java，正确解析WorkSP的完整JSON结构：

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializer;
import com.google.gson.stream.JsonReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.List;

public class App {
    public static void main(String[] args) throws FileNotFoundException {
        JsonReader readerTest = new JsonReader(new FileReader("test.json"));
        
        Gson gSonInstance = new GsonBuilder()
                .registerTypeAdapter(WorkSP.class, (JsonDeserializer<WorkSP>) (json, type, context) -> {
                    WorkSP workSP = new WorkSP();
                    // 解析workID字段
                    workSP.setWorkID(json.getAsJsonObject().get("workID").getAsLong());
                    // 调用context解析contributors列表，自动使用Contributor的反序列化器处理每个元素
                    workSP.setContributors(context.deserialize(json.getAsJsonObject().get("contributors"), List.class));
                    return workSP;
                })
                .create();
                
        WorkSP work = gSonInstance.fromJson(readerTest, WorkSP.class);
        
        // 测试输出验证
        System.out.println("WorkID: " + work.getWorkID());
        for (Contributor c : work.getContributors()) {
            System.out.println(String.format("贡献者：%s，关联WorkID：%d", c.getFullName(), c.getWorkID().getWorkID()));
        }
    }
}

关键说明 #

• 若JSON中的workID和workContributorID是业务主键，需删除实体类中的@GeneratedValue(strategy = GenerationType.IDENTITY)，避免数据库自增覆盖传入的业务ID。
• 持久化时，可通过JPA的EntityManager将解析后的WorkSP对象存入数据库，cascade = CascadeType.ALL会自动级联保存关联的Contributor数据。

内容的提问来源于stack exchange，提问作者J Robes