Spring HATEOAS嵌入式資源支持

Question

我想使用REST API的HAL格式來包含嵌入式資源 。 我正在使用Spring HATEOAS作為我的API，Spring HATEOAS似乎支持嵌入式資源; 但是，沒有關於如何使用它的文檔或示例。

有人可以舉例說明如何使用Spring HATEOAS來包含嵌入式資源嗎？

Answer 1

請務必閱讀Spring 關於HATEOAS的文檔 ，它有助於獲得基礎知識。

在這個答案中 ，核心開發人員指出了Resource ， Resources和PagedResources的概念，這是文檔未涵蓋的必要內容。

我花了一些時間來了解它是如何工作的，所以讓我們通過一些例子讓它變得清晰。

返回單一資源

資源

import org.springframework.hateoas.ResourceSupport;


public class ProductResource extends ResourceSupport{
    final String name;

    public ProductResource(String name) {
        this.name = name;
    }
}

控制器

import org.springframework.hateoas.Link;
import org.springframework.hateoas.Resource;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {
    @RequestMapping("products/{id}", method = RequestMethod.GET)
    ResponseEntity<Resource<ProductResource>> get(@PathVariable Long id) {
        ProductResource productResource = new ProductResource("Apfelstrudel");
        Resource<ProductResource> resource = new Resource<>(productResource, new Link("http://example.com/products/1"));
        return ResponseEntity.ok(resource);
    }
}

響應

{
    "name": "Apfelstrudel",
    "_links": {
        "self": { "href": "http://example.com/products/1" }
    }
}

返回多個資源

Spring HATEOAS附帶了嵌入式支持， Resources使用它來反映具有多個資源的響應。

    @RequestMapping("products/", method = RequestMethod.GET)
    ResponseEntity<Resources<Resource<ProductResource>>> getAll() {
        ProductResource p1 = new ProductResource("Apfelstrudel");
        ProductResource p2 = new ProductResource("Schnitzel");

        Resource<ProductResource> r1 = new Resource<>(p1, new Link("http://example.com/products/1"));
        Resource<ProductResource> r2 = new Resource<>(p2, new Link("http://example.com/products/2"));

        Link link = new Link("http://example.com/products/");
        Resources<Resource<ProductResource>> resources = new Resources<>(Arrays.asList(r1, r2), link);

        return ResponseEntity.ok(resources);
    }

響應

{
    "_links": {
        "self": { "href": "http://example.com/products/" }
    },
    "_embedded": {
        "productResources": [{
            "name": "Apfelstrudel",
            "_links": {
                "self": { "href": "http://example.com/products/1" }
            }, {
            "name": "Schnitzel",
            "_links": {
                "self": { "href": "http://example.com/products/2" }
            }
        }]
    }
}

如果要更改關鍵productResources ，則需要注釋資源：

@Relation(collectionRelation = "items")
class ProductResource ...

使用嵌入式資源返回資源

這是你需要開始皮條客彈簧的時候。 該HALResource通過@克里斯-達摩在推出另一個答案完全適合。

public class OrderResource extends HalResource {
    final float totalPrice;

    public OrderResource(float totalPrice) {
        this.totalPrice = totalPrice;
    }
}

控制器

    @RequestMapping(name = "orders/{id}", method = RequestMethod.GET)
    ResponseEntity<OrderResource> getOrder(@PathVariable Long id) {
        ProductResource p1 = new ProductResource("Apfelstrudel");
        ProductResource p2 = new ProductResource("Schnitzel");

        Resource<ProductResource> r1 = new Resource<>(p1, new Link("http://example.com/products/1"));
        Resource<ProductResource> r2 = new Resource<>(p2, new Link("http://example.com/products/2"));
        Link link = new Link("http://example.com/order/1/products/");

        OrderResource resource = new OrderResource(12.34f);
        resource.add(new Link("http://example.com/orders/1"));

        resource.embed("products", new Resources<>(Arrays.asList(r1, r2), link));

        return ResponseEntity.ok(resource);
    }

響應

{
    "_links": {
        "self": { "href": "http://example.com/products/1" }
    },
    "totalPrice": 12.34,
    "_embedded": {
        "products":     {
            "_links": {
                "self": { "href": "http://example.com/orders/1/products/" }
            },
            "_embedded": {
                "items": [{
                    "name": "Apfelstrudel",
                    "_links": {
                        "self": { "href": "http://example.com/products/1" }
                    }, {
                    "name": "Schnitzel",
                    "_links": {
                        "self": { "href": "http://example.com/products/2" }
                    }
                }]
            }
        }
    }
}

Answer 2

Pre HATEOAS 1.0.0M1：我找不到正式的方法來做到這一點......這就是我們所做的

public abstract class HALResource extends ResourceSupport {

    private final Map<String, ResourceSupport> embedded = new HashMap<String, ResourceSupport>();

    @JsonInclude(Include.NON_EMPTY)
    @JsonProperty("_embedded")
    public Map<String, ResourceSupport> getEmbeddedResources() {
        return embedded;
    }

    public void embedResource(String relationship, ResourceSupport resource) {

        embedded.put(relationship, resource);
    }  
}

然后我們的資源擴展了HALResource

更新：在HATEOAS 1.0.0M1中EntityModel（實際上是任何擴展RepresentationalModel的東西）現在只要嵌入式資源通過getContent公開（或者你讓jackson序列化一個內容屬性），就可以原生支持它。 喜歡：

    public class Result extends RepresentationalModel<Result> {
        private final List<Object> content;

        public Result(

            List<Object> content
        ){

            this.content = content;
        }

        public List<Object> getContent() {
            return content;
        }
    };

    EmbeddedWrappers wrappers = new EmbeddedWrappers(false);
    List<Object> elements = new ArrayList<>();

    elements.add(wrappers.wrap(new Product("Product1a"), LinkRelation.of("all")));
    elements.add(wrappers.wrap(new Product("Product2a"), LinkRelation.of("purchased")));
    elements.add(wrappers.wrap(new Product("Product1b"), LinkRelation.of("all")));

    return new Result(elements);

你會得到

{
 _embedded: {
   purchased: {
    name: "Product2a"
   },
  all: [
   {
    name: "Product1a"
   },
   {
    name: "Product1b"
   }
  ]
 }
}

Answer 3

這是我們發現的一個小例子。 首先我們使用spring-hateoas-0.16

成像我們有GET /profile應返回帶有嵌入式電子郵件列表的用戶配置文件。

我們有電子郵件資源。

@Data
@JsonIgnoreProperties(ignoreUnknown = true)
@Relation(value = "email", collectionRelation = "emails")
public class EmailResource {
    private final String email;
    private final String type;
}

我們想要嵌入到個人資料響應中的兩封電子郵件

Resource primary = new Resource(new Email("neo@matrix.net", "primary"));
Resource home = new Resource(new Email("t.anderson@matrix.net", "home"));

為了表明嵌入了這些資源，我們需要一個EmbeddedWrappers實例：

import org.springframework.hateoas.core.EmbeddedWrappers
EmbeddedWrappers wrappers = new EmbeddedWrappers(true);

在wrappers的幫助下，我們可以為每封電子郵件創建EmbeddedWrapper實例並將它們放入列表中。

List<EmbeddedWrapper> embeddeds = Arrays.asList(wrappers.wrap(primary), wrappers.wrap(home))

剩下要做的就是用這些嵌入式構建我們的配置文件資源。 在下面的示例中，我使用lombok來縮短代碼。

@Data
@Relation(value = "profile")
public class ProfileResource {
    private final String firstName;
    private final String lastName;
    @JsonUnwrapped
    private final Resources<EmbeddedWrapper> embeddeds;
}

請記住在嵌入式字段上注釋@JsonUnwrapped

我們准備從控制器返回所有這些

...
Resources<EmbeddedWrapper> embeddedEmails = new Resources(embeddeds, linkTo(EmailAddressController.class).withSelfRel());
return ResponseEntity.ok(new Resource(new ProfileResource("Thomas", "Anderson", embeddedEmails), linkTo(ProfileController.class).withSelfRel()));
}

現在在我們的回應中

{
"firstName": "Thomas",
"lastName": "Anderson",
"_links": {
    "self": {
        "href": "http://localhost:8080/profile"
    }
},
"_embedded": {
    "emails": [
        {
            "email": "neo@matrix.net",
            "type": "primary"
        },
        {
            "email": "t.anderson@matrix.net",
            "type": "home"
        }
    ]
}
}

使用Resources<EmbeddedWrapper> embeddeds有趣之處在於，您可以在其中放置不同的資源，並且它將根據關系自動對它們進行分組。 為此，我們使用org.springframework.hateoas.core包中的注釋@Relation 。

還有一篇關於HAL中嵌入式資源的好文章

Answer 4

通常，HATEOAS需要創建一個代表REST輸出的POJO並擴展HATEOAS提供的ResourceSupport。 可以在不創建額外POJ的情況下直接使用Resource，Resources和Link類，如下面的代碼所示：

@RestController
class CustomerController {

    List<Customer> customers;

    public CustomerController() {
        customers = new LinkedList<>();
        customers.add(new Customer(1, "Peter", "Test"));
        customers.add(new Customer(2, "Peter", "Test2"));
    }

    @RequestMapping(value = "/customers", method = RequestMethod.GET, produces = "application/hal+json")
    public Resources<Resource> getCustomers() {

        List<Link> links = new LinkedList<>();
        links.add(linkTo(methodOn(CustomerController.class).getCustomers()).withSelfRel());
        List<Resource> resources = customerToResource(customers.toArray(new Customer[0]));

        return new Resources<>(resources, links);

    }

    @RequestMapping(value = "/customer/{id}", method = RequestMethod.GET, produces = "application/hal+json")
    public Resources<Resource> getCustomer(@PathVariable int id) {

        Link link = linkTo(methodOn(CustomerController.class).getCustomer(id)).withSelfRel();

        Optional<Customer> customer = customers.stream().filter(customer1 -> customer1.getId() == id).findFirst();

        List<Resource> resources = customerToResource(customer.get());

        return new Resources<Resource>(resources, link);

    }

    private List<Resource> customerToResource(Customer... customers) {

        List<Resource> resources = new ArrayList<>(customers.length);

        for (Customer customer : customers) {
            Link selfLink = linkTo(methodOn(CustomerController.class).getCustomer(customer.getId())).withSelfRel();
            resources.add(new Resource<Customer>(customer, selfLink));
        }

        return resources;
    }
}

Answer 5

結合上面的答案，我做了一個更容易的方法：

return resWrapper(domainObj, embeddedRes(domainObj.getSettings(), "settings"))

這是一個自定義實用程序類（見下文）。 注意：

• 的第二個參數resWrapper接受...的embeddedRes調用。
• 您可以創建另一個省略resWrapper的關系字符串的resWrapper 。
• embeddedRes第一個參數是Object ，因此您還可以提供ResourceSupport的實例
• 表達式的結果是擴展Resource<DomainObjClass>的類型。 因此，它將由所有Spring Data REST ResourceProcessor<Resource<DomainObjClass>> 。 您可以創建它們的集合，並包裝new Resources<>() 。

創建實用程序類：

import com.fasterxml.jackson.annotation.JsonUnwrapped;
import java.util.Arrays;
import org.springframework.hateoas.Link;
import org.springframework.hateoas.Resource;
import org.springframework.hateoas.Resources;
import org.springframework.hateoas.core.EmbeddedWrapper;
import org.springframework.hateoas.core.EmbeddedWrappers;

public class ResourceWithEmbeddable<T> extends Resource<T> {

    @SuppressWarnings("FieldCanBeLocal")
    @JsonUnwrapped
    private Resources<EmbeddedWrapper> wrappers;

    private ResourceWithEmbeddable(final T content, final Iterable<EmbeddedWrapper> wrappers, final Link... links) {

        super(content, links);
        this.wrappers = new Resources<>(wrappers);
    }


    public static <T> ResourceWithEmbeddable<T> resWrapper(final T content,
                                                           final EmbeddedWrapper... wrappers) {

        return new ResourceWithEmbeddable<>(content, Arrays.asList(wrappers));

    }

    public static EmbeddedWrapper embeddedRes(final Object source, final String rel) {
        return new EmbeddedWrappers(false).wrap(source, rel);
    }
}

您只需要在您的服務類中包含import static package.ResourceWithEmbeddable.*即可使用它。

JSON看起來像這樣：

{
    "myField1": "1field",
    "myField2": "2field",
    "_embedded": {
        "settings": [
            {
                "settingName": "mySetting",
                "value": "1337",
                "description": "umh"
            },
            {
                "settingName": "other",
                "value": "1488",
                "description": "a"
            },...
        ]
    }
}

Answer 6

Spring將提供構建器https://github.com/spring-projects/spring-hateoas/issues/864

Answer 7

這就是我用spring-boot-starter-hateoas 2.1.1構建這樣的json的方法：

{
    "total": 2,
    "count": 2,
    "_embedded": {
        "contacts": [
            {
                "id": "1-1CW-303",
                "role": "ASP",
                "_links": {
                    "self": {
                        "href": "http://localhost:8080/accounts/2700098669/contacts/1-1CW-303"
                    }
                }
            },
            {
                "id": "1-1D0-267",
                "role": "HSP",
                "_links": {
                    "self": {
                        "href": "http://localhost:8080/accounts/2700098669/contacts/1-1D0-267"
                    }
                }
            }
        ]
    },
    "_links": {
        "self": {
            "href": "http://localhost:8080/accounts/2700098669/contacts?limit=2&page=1"
        },
        "first": {
            "href": "http://localhost:8080/accounts/2700098669/contacts?limit=2&page=1"
        },
        "last": {
            "href": "http://localhost:8080/accounts/2700098669/contacts?limit=2&page=1"
        }
    }
}

封裝所有這些字段的主類是

public class ContactsResource extends ResourceSupport{
    private long count;
    private long total;
    private final Resources<Resource<SimpleContact>> contacts;

    public long getTotal() {
        return total;
    }

    public ContactsResource(long total, long count, Resources<Resource<SimpleContact>> contacts){
        this.contacts = contacts;
        this.total = total;
        this.count = count;
    }

    public long getCount() {
        return count;
    }

    @JsonUnwrapped
    public Resources<Resource<SimpleContact>> getContacts() {
        return contacts;
    }
}

SimpleContact有關於單個聯系人的信息，它只是pojo

@Relation(value = "contact", collectionRelation = "contacts")
public class SimpleContact {
    private String id;
    private String role;

    public String getId() {
        return id;
    }

    public SimpleContact id(String id) {
        this.id = id;
        return this;
    }

    public String getRole() {
        return role;
    }

    public SimpleContact role(String role) {
        this.role = role;
        return this;
    }
}

並創建ContactsResource：

public class ContactsResourceConverter {

    public static ContactsResource toResources(Page<SimpleContact> simpleContacts, Long accountId){

        List<Resource<SimpleContact>> embeddeds = simpleContacts.stream().map(contact -> {
            Link self = linkTo(methodOn(AccountController.class).getContactById(accountId, contact.getId())).
                    withSelfRel();
            return new Resource<>(contact, self);
        }
        ).collect(Collectors.toList());

        List<Link> listOfLinks = new ArrayList<>();
        //self link
        Link selfLink = linkTo(methodOn(AccountController.class).getContactsForAccount(
                accountId,
                simpleContacts.getPageable().getPageSize(),
                simpleContacts.getPageable().getPageNumber() + 1)) // +1 because of 0 first index
                .withSelfRel();
        listOfLinks.add(selfLink);

        ... another links           

        Resources<Resource<SimpleContact>> resources = new Resources<>(embeddeds);
        ContactsResource contactsResource = new ContactsResource(simpleContacts.getTotalElements(), simpleContacts.getNumberOfElements(), resources);
        contactsResource.add(listOfLinks);

        return contactsResource;
    }
}

而我只是從控制器這樣調用它：

return new ResponseEntity<>(ContactsResourceConverter.toResources(simpleContacts, accountId), HttpStatus.OK);

Answer 8

在您的pom中添加此依賴項。 請訪問此鏈接： https ： //www.baeldung.com/spring-rest-hal

<dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-rest-hal-browser</artifactId>
</dependency>

它會像這樣改變你的反應。

"_links": {
    "next": {
        "href": "http://localhost:8082/mbill/user/listUser?extra=ok&page=11"
    }
}