我有一个使用 Hateoas 的 Rest-Service，它在没有分页的情况下工作。现在我正在制作可分页的 Json。我使用 Spring-Hateoas 的开箱即用功能来完成它。但现在我坚持使用它，我想它真的没有很好的记录，如果有的话。

我的 JSON 如下所示:

{
"_embedded": {
"vertragResourceList": [
  {
    "identifier": 728,
    "auszubildender": "Rumm",
    "beruf": "Landwirt/in",
    "betrieb": "Mitterbauer Johann",
    "betriebsNummer": "e12d0949-67ae-4134-9dc2-fb67758b6b16",
    "zustaendigeStelle": "Irgendwo",
    "beginn": 529887600000,
    "status": "RECENT",
    "fachrichtung": null,
    "schwerpunkt": "Grünland oder Ackergras",
    "ende": 623113200000,
    "_links": {
      "self": {
        "href": "http://localhost:8080/bbsng-app-rest/vertrag/728"
      }
    }
  },
  {
    "identifier": 803,
    "auszubildender": "Gossen",
    "beruf": "Landwirt/in",
    "betrieb": "Beer Johann",
    "betriebsNummer": "d5a20cb9-7273-4b75-85bd-f8e7d6a843c4",
    "zustaendigeStelle": "Woanders",
    "beginn": 278118000000,
    "status": "RECENT",
    "fachrichtung": null,
    "schwerpunkt": "Ackerfutterbau",
    "ende": 339116400000,
    "_links": {
      "self": {
        "href": "http://localhost:8080/bbsng-app-rest/vertrag/803"
      }
    }
  }
]
},
"page": {
"size": 2,
"totalElements": 1000,
"totalPages": 500,
"number": 5
}
}

====

但是现在我的列表是“_embedded”，所以我怎样才能以最方便的方式使用它。我更喜欢 Spring-Hateoas 或类似的开箱即用的解决方案。

我之前的代码如下所示(Json 之前没有包装在 _embedded/vertragResourceList 中!!!)。

@Override
@SuppressWarnings({ "unchecked", "rawtypes" })
public VertragsListe findeAlleVertraege(final Integer firstDataSet, final Integer lastDataSet, final VertragDTFilter vertragsFilter,
        final VertragDTSorting vertragSorting) {
    final VertragsListe vertragsListe = new VertragsListe();
    final String url = LinkUtils.findeVertrag(firstDataSet, lastDataSet, vertragsFilter, vertragSorting);
    final ResponseEntity<List> entity = template.getForEntity(url, List.class);

    if (OK.equals(entity.getStatusCode())) {
        final List<LinkedHashMap> body = entity.getBody();
        for (final LinkedHashMap map : body) {
            vertragsListe.add(getPopulatedVertrag(vertragsListe, map));
        }
    }

    return vertragsListe;
}

堆栈跟踪:

org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@e89d61c; line: 1, column: 1]; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@e89d61c; line: 1, column: 1]

=====

编辑:

相应的资源类如下所示(服务器端和客户端!!!):

public class VertragPagedResources extends PagedResources<VertragResource> {

    @SuppressWarnings("unchecked")
    public VertragPagedResources(final Collection<VertragResource> content, final PageMetadata metadata) {
        super(content, metadata, CollectionUtils.EMPTY_COLLECTION);
    }

    public VertragPagedResources() {
        super();
    }

}

在客户端我现在改变了:

@Autowired private RestTemplate template;

@Override
public VertragPagedResources findeAlleVertraege(final Integer firstDataSet, final Integer lastDataSet, final VertragDTFilter vertragsFilter,
        final VertragDTSorting vertragSorting) {
    final String url = LinkUtils.findeVertrag(firstDataSet, lastDataSet, vertragsFilter, vertragSorting);
    final ResponseEntity<VertragPagedResources> entity = template.getForEntity(url, VertragPagedResources.class);

    if (OK.equals(entity.getStatusCode())) {
        return entity.getBody();
    }

    return new VertragPagedResources();
}

现在我没有得到任何异常，但内容是空的。唯一正确填写的是来自可分页的信息(numberOfReturned Datasets、pageSize 等)。 内容为空List!!! 调试时，我在浏览器中尝试给定的 URL，然后 JSON 看起来像上面提到的那样。

<200 OK,PagedResource { content: [], metadata: Metadata { number: 1, total pages: 100, total elements: 1000, size: 10 }, links: [] },{Server=[Apache-Coyote/1.1], X-Application-Context=[application:custom:8080], totalNumber=[1000], Content-Type=[application/json;charset=UTF-8], Transfer-Encoding=[chunked], Date=[Wed, 28 Jan 2015 16:58:16 GMT]}>

VertragResource(客户端和服务器):

public class VertragResource extends IdentifierResourceSupport {

  @NotNull private String auszubildender;
  @NotNull private String beruf;
  @NotNull private String betrieb;
  @NotNull private String betriebsNummer;
  @NotNull private String zustaendigeStelle;
  @NotNull private Calendar beginn;
  @NotNull private String status;

  private String fachrichtung;
  private String schwerpunkt;
  private Calendar ende;

  // GETTER & SETTER ....

Controller 服务器端:

@RequestMapping(method = GET, produces = MediaType.APPLICATION_JSON_VALUE)
public HttpEntity<VertragPagedResources> showAll( /*  PARAMS  */ ) { 

    // FILTER ...
    final VertragFilter filter = new VertragFilter();
    // FILL FILTER

    // SORTING ...
    final VertragSorting sorting = new VertragSorting(/* BLA */)

    // COMPUTE ...
    final VertragResourceAssembler assembler = new VertragResourceAssembler();
    final List<Vertrag> alleVertrage = service.findeAlleVertraege(/* BLA */);
    final List<VertragResource> resources = assembler.toResources(alleVertrage);

    //

    final long totalElements = service.zaehleAlleVertraege(filter);
    final long size = Math.min(displayLength, totalElements);
    final long totalPages = totalElements / size;
    final PageMetadata pageMetadata = new PageMetadata(displayLength, displayStart, totalElements, totalPages);
    final VertragPagedResources pagedResources = new VertragPagedResources(resources, pageMetadata);
    return new HttpEntity<VertragPagedResources>(pagedResources, headerTotalNumberOfData());
}

====

标识符资源支持:

public class IdentifierResourceSupport extends ResourceSupport {
    private Long identifier;

    public Long getIdentifier() {
        return identifier;
    }

    public void setIdentifier(Long identifier) {
       this.identifier = identifier;
    }
}

=====

编辑 2:

我现在所做的是，将 Spring-Boot 从 1.2.1 切换回 1.1.10。现在我在尝试相同的时候得到了一个异常，似乎 Spring-Boot 1.2.1 隐藏了异常:

org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: Unrecognized field "_embedded" (class at.compax.bbsng.client.mvc.client.resource.VertragPagedResources), not marked as ignorable (3 known properties: "links", "content", "page"])
 at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@62532c56; line: 1, column: 15] (through reference chain: at.compax.bbsng.client.mvc.client.resource.VertragPagedResources["_embedded"]); nested exception is com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "_embedded" (class at.compax.bbsng.client.mvc.client.resource.VertragPagedResources), not marked as ignorable (3 known properties: "links", "content", "page"])
 at [Source: sun.net.www.protocol.http.HttpURLConnection$HttpInputStream@62532c56; line: 1, column: 15] (through reference chain: at.compax.bbsng.client.mvc.client.resource.VertragPagedResources["_embedded"])

最佳答案

好的，

我现在找到了解决方案。

首先，Spring Boot 1.2.1有一个BUG。就像问题 EDIT2 中提到的那样。 Spring-Boot 1.1.10 抛出异常，因为它无法映射_embedded 中的内容。这就是为什么我的内容保持空白。 Spring Boot 1.2.1 只是将其留空，没有任何提示作为异常。降级到 1.1.10 给了我提示。

那么改变的结果是什么:

服务器端 Controller :

@RequestMapping(method = GET, produces = "application/hal+json")
public HttpEntity<VertragPagedResources> showAll( /* PARAMS */  ) { 

    // LIKE CODE IN QUESTION ...

    return new HttpEntity<VertragPagedResources>(pagedResources);
}

====

RestTemplate 配置:

然后您需要配置您的 Resttemplate 来处理 HAL 格式。

@Bean
public RestTemplate restTemplate() {
    final ObjectMapper mapper = new ObjectMapper();
    mapper.registerModule(new Jackson2HalModule());

    final MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    converter.setSupportedMediaTypes(MediaType.parseMediaTypes("application/hal+json"));
    converter.setObjectMapper(mapper);

    return new RestTemplate(Collections.<HttpMessageConverter<?>> singletonList(converter));
}

客户端代码与问题中的第一个编辑保持相同!

关于java - 使用 Spring Hateoas 可分页，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28116175/