REST HATEOAS：如何序列化嵌套資源（使用Spring HATEOAS）？

Question

我使用Spring HATEOAS在我的應用程序中創建REST HATEOAS API。 到目前為止，它運行良好，但是在嵌套資源方面我還是很困惑。 將這樣的類層次結構映射到REST HATEOAS資源的正確方法是：

public class MyEntity {

    private int id;

    private List<ChildEntity> children;

}


public class ChildEntity {

    private int id;

    private AnotherEntity entity;

}


public class AnotherEntity {
}

我為所有這些實體創建了Resource類，但是在序列化MyEntity時，所有包含的實體都被序列化為POJO，盡管我也需要將它們序列化為資源（帶有鏈接等）。 有沒有一種方法可以將資源添加到父資源（而不使用Resources類）？ 還是我必須向孩子添加@JsonIgnore，然后在ResourceAssembler中手動將孩子添加為資源？ 那么使用ResourceSupport而不是Resource更有意義嗎？

Answer 1

擴展ResourceSupport：

public class MyEntityResource extends ResourceSupport {

    private int identificator;

    private List<ChildEntityResource> children;

    public int getIdentificator() {
        return identificator;
    }

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

    public List<ChildEntityResource> getChildren() {
        return children;
    }

    public void setChildren(List<ChildEntityResource> children) {
        this.children = children;
    }

}

---

public class ChildEntityResource extends ResourceSupport {

    private int identificator;

    private AnotherEntityResource entity;

    public int getIdentificator() {
        return identificator;
    }

    public void setIdentificator(int identificator) {
        this.identificator = identificator;
    }

    public AnotherEntityResource getEntity() {
        return entity;
    }

    public void setEntity(AnotherEntityResource entity) {
        this.entity = entity;
    }
}

---

public class AnotherEntityResource extends ResourceSupport {

    private String value;


    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

---

@RestController
public class EntityController {
    @RequestMapping(value = "/entity", method = RequestMethod.GET)
    public ResponseEntity<MyEntityResource> index() {

        AnotherEntityResource anotherEntityResource  = new AnotherEntityResource();
        anotherEntityResource.add(new Link("link-for-another-entity-resource", "rel-1"));

        anotherEntityResource.setValue("value for Another Entity","rel-2");

        ChildEntityResource childEntityResource = new ChildEntityResource();
        childEntityResource.setIdentificator(20);
        childEntityResource.setEntity(anotherEntityResource);
        childEntityResource.add(new Link("link-for-child-entity-resource", "rel-3"));

        MyEntityResource entityResource = new MyEntityResource();

        entityResource.setIdentificator(100);
        entityResource.setChildren(Arrays.asList(childEntityResource));
        entityResource.add(new Link("link-for-entity-resource"));

        return new ResponseEntity<MyEntityResource>(entityResource,  HttpStatus.OK);
    }

}

---

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
         SpringApplication.run(Application.class, args);
    }

}

結果是：

{
     "identificator": 100,
     "children": [
         {
             "identificator": 20,
             "entity": {
                 "value": "value for Another Entity",
                 "_links": {
                     "rel-1": {
                         "href": "link-for-another-entity-resource"
                    }
                }
            },
            "_links": {
                "rel-2": {
                    "href": "link-for-child-entity-resource"
                } 
            }
        }
    ],
    "_links": {
        "rel-3": {
            "href": "link-for-entity-resource"
        }
    }
}

但是您必須考慮這是否是連接不同資源的正確選擇。 除非您在控制器中提供方法來獲取此嵌入式資源，否則您將無法單獨訪問它們。 一種解決方案是使用HAL。 使用HAL，您可以使用_links屬性指向資源，也可以將此資源嵌入_embedded屬性。