java - 无法使用 Jersey 客户端解码 JSON 对象数组

Question

我正在尝试解码的单元素 JSON 数组:

[
   {
      "id":"42",
      "status":"Active",
      "name":"purple monkey dishwasher"
   }
]

对应的 Java 类(为简洁起见省略了 getter 和 setter):

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Badge
{
    @XmlElement(name="id")
    private String id;

    @XmlElement(name="status")
    private Status status;

    @XmlElement(name="name")
    private String name;

    public static enum Status
    {
        Active,
        NotActive
    }
}

发出 HTTP 请求的 Jersey 客户端代码应该将上述 JSON 解码为单元素 List<Foo>:

Client client = Client.create();
WebResource apiRoot = client.resource("http://localhost:9000/api");
List<Badge> badges = apiRoot.path("/badges").get(new GenericType<List<Badge>>(){});

最后一行，特别是 WebResource#get() 调用，抛出以下异常:

javax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"status"). Expected elements are <{}badge>
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.handleEvent(UnmarshallingContext.java:662)
    at com.sun.xml.bind.v2.runtime.unmarshaller.Loader.reportError(Loader.java:258)
    at com.sun.xml.bind.v2.runtime.unmarshaller.Loader.reportError(Loader.java:253)
    at com.sun.xml.bind.v2.runtime.unmarshaller.Loader.reportUnexpectedChildElement(Loader.java:120)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext$DefaultRootLoader.childElement(UnmarshallingContext.java:1063)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext._startElement(UnmarshallingContext.java:498)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.startElement(UnmarshallingContext.java:480)
    at com.sun.xml.bind.v2.runtime.unmarshaller.InterningXmlVisitor.startElement(InterningXmlVisitor.java:75)
    at com.sun.xml.bind.v2.runtime.unmarshaller.StAXStreamConnector.handleStartElement(StAXStreamConnector.java:247)
    at com.sun.xml.bind.v2.runtime.unmarshaller.StAXStreamConnector.bridge(StAXStreamConnector.java:181)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal0(UnmarshallerImpl.java:369)
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.java:341)
    at com.sun.jersey.core.provider.jaxb.AbstractListElementProvider.readFrom(AbstractListElementProvider.java:232)
    at com.sun.jersey.api.client.ClientResponse.getEntity(ClientResponse.java:552)
    at com.sun.jersey.api.client.ClientResponse.getEntity(ClientResponse.java:522)
    at com.sun.jersey.api.client.WebResource.handle(WebResource.java:617)
    at com.sun.jersey.api.client.WebResource.get(WebResource.java:191)
    at com.redacted.badge.client.BadgerImpl.findAllBadges(BadgerImpl.java:105)
    at com.redacted.webapp.admin.BadgeAction.unspecified(BadgeAction.java:40)
    at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:245)
    at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:170)
    at org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:58)
    at org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:67)
    at org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:51)
    at org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    at org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
    at org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
    at org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:283)
    at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
    at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:119)
    at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:55)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.redacted.webapp.filter.MemberFilter.doFilter(MemberFilter.java:83)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.redacted.webapp.filter.AuthFilter.doFilter(AuthFilter.java:113)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.displaytag.filter.ResponseOverrideFilter.doFilter(ResponseOverrideFilter.java:125)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.redacted.webapp.filter.LanguageHandlingFilter.doFilter(LanguageHandlingFilter.java:151)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.redacted.webapp.filter.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:146)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.redacted.webapp.filter.PartnerFilter.doFilter(PartnerFilter.java:59)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at com.redacted.webapp.filter.SessionStatusFilter.doFilter(SessionStatusFilter.java:113)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:470)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at com.googlecode.psiprobe.Tomcat60AgentValve.invoke(Tomcat60AgentValve.java:30)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:680)

我在 Badge 上尝试了各种注释组合，或者使用数组代替 GenericType :

List<Badge> badges = Arrays.asList(apiRoot.path("/badges").get(Badge[].class));

或使用中间 ClientResponse :

GenericType<List<Badge>> type = new GenericType<List<Badge>>(){};
ClientResponse clientResponse = apiRoot.path("/badges").get(ClientResponse.class);
List<Badge> badges = clientResponse.getEntity(type);

但目前还没有解决问题。

更令人困惑的是，我现有的设置没有问题解码其他结构内的 JSON 编码的 Badge ，如下所示:

{
   "userid":"123456789",
   "userbadges":[
      {
         "badge":{
              "id":"42",
              "status":"Active",
              "name":"purple monkey dishwasher"
         },
         "earned":"2012-03-06 18:16:18.172"
      }
   ]
}

我做错了什么？

Answer 1

我可以通过使用 JacksonJsonProvider 以最小的努力解决这个问题。作为 Jersey 客户端实例的 MessageBody(Reader|Writer) 提供程序:

ClientConfig cfg = new DefaultClientConfig();
cfg.getClasses().add(JacksonJsonProvider.class);
Client client = Client.create(cfg);

Jackson 的 MessageBodyReader 实现似乎比 Jersey JSON 实现更好。

感谢 How can I customize serialization of a list of JAXB objects to JSON?为我指明 jackson 的方向。