使用Retrofit按ID获取数据时遇JsonSyntaxException报错求助

报错信息 #

com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 2 path $

学生实体类代码 #

public class Students implements Parcelable {
    private int id;
    @SerializedName("first_name")
    private String firstName;
    @SerializedName("last_name")
    private String lastName;
    private String course;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getCourse() {
        return course;
    }

    public void setCourse(String course) {
        this.course = course;
    }

    public String getScore() {
        return score;
    }

    public void setScore(String score) {
        this.score = score;
    }

    private String score;

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(this.id);
        dest.writeString(this.firstName);
        dest.writeString(this.lastName);
        dest.writeString(this.course);
        dest.writeString(this.score);
    }

    public void readFromParcel(Parcel source) {
        this.id = source.readInt();
        this.firstName = source.readString();
        this.lastName = source.readString();
        this.course = source.readString();
        this.score = source.readString();
    }

    public Students() {
    }

    protected Students(Parcel in) {
        this.id = in.readInt();
        this.firstName = in.readString();
        this.lastName = in.readString();
        this.course = in.readString();
        this.score = in.readString();
    }

    public static final Parcelable.Creator<Students> CREATOR = new Parcelable.Creator<Students>() {
        @Override
        public Students createFromParcel(Parcel source) {
            return new Students(source);
        }

        @Override
        public Students[] newArray(int size) {
            return new Students[size];
        }
    };
}

Retrofit接口代码 #

public interface Api {
    @GET(url)
    Single<Students> getStudent(@Query("id") int id);
}

MainActivity请求代码 #

Retrofit retrofit = new Retrofit.Builder()
        .baseUrl(URL)
        .addConverterFactory(GsonConverterFactory.create())
        .addCallAdapterFactory(RxJava3CallAdapterFactory.create())
        .build();

Api api = retrofit.create(Api.class);

api.getStudent(339).subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()).subscribe(new SingleObserver<Students>() {
    @Override
    public void onSubscribe(@NonNull Disposable d) {

    }

    @Override
    public void onSuccess(@NonNull Students students) {
        Log.i(TAG, "onSuccess: "+students);
    }

    @Override
    public void onError(@NonNull Throwable e) {
        Log.e(TAG, "onError: "+e );
    }
});

错误原因及解决方案 #

错误原因

报错核心是：Gson期望解析单个Students对象（对应JSON的BEGIN_OBJECT），但后端接口实际返回的是包含学生数据的JSON数组（对应BEGIN_ARRAY），数据类型不匹配导致解析失败。

解决方案

有两种可行处理方式：

1. 适配后端返回的数组格式
   修改Retrofit接口的返回类型为Single<List<Students>>，同时调整订阅回调的接收逻辑：

   // 修改后的Api接口
   public interface Api {
       @GET(url)
       Single<List<Students>> getStudent(@Query("id") int id);
   }
   

   // 修改后的订阅代码
   api.getStudent(339)
     .subscribeOn(Schedulers.io())
     .observeOn(AndroidSchedulers.mainThread())
     .subscribe(new SingleObserver<List<Students>>() {
         @Override
         public void onSubscribe(@NonNull Disposable d) {}
   
         @Override
         public void onSuccess(@NonNull List<Students> studentsList) {
             // 根据ID查询应仅返回一条数据，直接取数组第一个元素
             if (!studentsList.isEmpty()) {
                 Students student = studentsList.get(0);
                 Log.i(TAG, "onSuccess: "+student);
             }
         }
   
         @Override
         public void onError(@NonNull Throwable e) {
             Log.e(TAG, "onError: "+e );
         }
     });
   

2. 要求后端调整返回格式
   如果后端支持修改，让其根据ID返回单个Students对象的JSON格式（而非数组），现有代码无需修改即可正常运行。

内容的提问来源于stack exchange，提问作者KMD