java - Spring Boot - 分层实体数据未从 REST API 返回

Question

我在 Spring Boot 中为类(class)实现了一个 API 方法。它按主题 ID 获取类(class)。 Course 类的实现如下:

@Entity
public class Course {

    @Id
    private String id;
    private String name;
    private String description;
    @ManyToOne
    private Topic topic;
    public Course() {

    }

    public Course(String id, String name, String description, String topicId) {
        super();
        this.id = id;
        this.name = name;
        this.description = description;
        this.topic = new Topic(topicId, "", "");
    }

    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getDescription() {
        return description;
    }
    public void setDescription(String description) {
        this.description = description;
    }

    public void setTopic(Topic t) {     
        this.topic = t;     
    }

}

API方法实现为:

@RequestMapping(method=RequestMethod.GET, value="/topics/{topicId}/courses")
    public RestMessage getAllCourses(@PathVariable String topicId) {                
        try {

            List<Course> course = courseService.getAllCourses(topicId);     
            message = new RestMessage(course,StatusCodeEnum.OK);        
            return message;

        } catch (Exception e) {

            message = new RestMessage(e.getMessage(),StatusCodeEnum.INTERNAL_SERVER_ERROR);
            message.setException(e);

            return message;         
        }       
    }

该方法实现很简单，它尝试根据主题 id 获取所有类(class)并将其作为 RestMessage 对象返回。我使用 postman 进行测试，在响应中我得到了类(class)列表，但主题实体数据被丢弃。

API响应如下:

{
    "data": [
        {
            "id": "java-streams",
            "name": "Java Streams",
            "description": "Java Stream learning"
        }
    ],
    "httpStatus": "OK",
    "statusCode": 200,
    "exception": null
}

RestMessage 类定义为:

public class RestMessage {

    private Object data;
    private StatusCodeEnum httpStatus;
    private int statusCode;
    private Exception ex;

    public RestMessage() {

    }

    public RestMessage(Object d, StatusCodeEnum c) {
        data = d;
        httpStatus = c;
        statusCode = c.val();
    }

    public void setData(Object d) {
        data =d;
    }

    public void setHttpStatus(StatusCodeEnum c) {
        httpStatus = c;
    }

    public void setStatusCode(int c) {
        statusCode = c;
    }

    public void setException(Exception e) {
        ex = e;
    }

    public void setStatusCode(StatusCodeEnum c) {
        httpStatus = c;
    }

    public Object getData() {
        return data;
    }

    public StatusCodeEnum getHttpStatus() {
        return httpStatus;
    }

    public Exception getException() {
        return ex;
    }

    public int getStatusCode() {
        return statusCode;
    }

}

但是，我尝试调试 API 端点，在返回 RestMessage 对象之前，我有所需形状的数据，但在获取 json 响应后，所有类(class)的 Topic 对象都会被截断。

附上调试数据图像:

我想知道在这种情况下我做错了什么？

Answer 1

Course 中的字段 topic 没有 getter，这就是 JSON 序列化程序忽略的原因。