Question

我们正在从我们的Web API返回的模型对象上使用JAXB Annotations，我们希望数据被本地化，并且其他值根据用户首选项（即度量与法规）进行格式化。我们通过向Marshaller添加自定义适配器来实现此目的。

Marshaller marshaller = jc.createMarshaller();
marshaller.setAdapter(NumberPersonalizedXmlAdapter.class,
          new NumberPersonalizedXmlAdapter(locale);
marshaller.marshal(expected, writer);

尝试最简单的方法我将从HTTP请求标头中获取Locale，并将其提供给MessageBodyWriter类之一的Marshaller。

我考虑扩展默认注册的提供程序，如XMLRootElementProvider，但意识到它们大部分是最终的，所以我放弃了这种方法。无论如何我至少需要延伸10个课程，因此这并不理想。

有没有人知道如何最好地在MessageBodyWriter中为每个请求设置客户适配器的marshaller？我很确定它与ContextResolver有关。

Answer 1

为编组编写ContextResolver会产生比编写MessageBodyWriter更清晰，更合适的解决方案。所有JAXB类都使用Providers.getContextResolver方法来获取编组器。我提供自定义ContextResolver，我有i18n回复。

@Provider
@Produces({ MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON })
public class JaxbPersonalizerContextResolver implements ContextResolver<Marshaller> {

    private HttpHeaders requestHeaders;

    public JaxbPersonalizerContextResolver(@Context HttpHeaders requestHeaders) {
        this.requestHeaders = requestHeaders;
    }

    @Override
    public Marshaller getContext(Class<?> type) {
        Locale locale = If.first(this.requestHeaders.
                                    getAcceptableLanguages(), Locale.US);
        NumberFormat formatter = NumberFormat.getNumberInstance(locale);
        formatter.setMaximumFractionDigits(1);

        Marshaller marshaller;
        try {
            JAXBContext jc = JAXBContext.newInstance(type);
            marshaller = jc.createMarshaller();
        } catch (JAXBException e) {
            throw new RuntimeException(e);
        }
        marshaller.setAdapter(QuantityXmlAdapter.class, 
                           new QuantityXmlAdapter.Builder().locale(locale).build());
        marshaller.setAdapter(NumberPersonalizedXmlAdapter.class,
                new NumberPersonalizedXmlAdapter.Builder().
                                    formatter(formatter).build());
        return marshaller;
    }
}

JSON没有被本地化，经过一些调查后，我意识到正在使用Jackson JSON库而不是与Jersey库一起分发的JAXBJSONElementProvider。我在web.xml中removed the POJOMappingFeature configuration并且我已经本地化了JSON，但是它不如Jackson JSON那么好。

一个非常干净的解决方案让我觉得JAX-RS和Jersey的实现做得很好。

Answer 2

我解决了编写我自己的MessageBodyWriter的问题，它接收了注入构造函数的HttpHeaders，我后来在编写响应时使用了它。我将包括整个班级，因为它不是那么大。

@Produces(MediaType.APPLICATION_XML)
@Provider
public class JaxbPersonalizationProvider implements MessageBodyWriter<Object> {

    private HttpHeaders requestHeaders;
    private Providers providers;

    public JaxbPersonalizationProvider(@Context HttpHeaders requestHeaders, @Context Providers providers) {
        this.requestHeaders = requestHeaders;
        this.providers = providers;
    }

    @Override
    public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        return type.getAnnotation(XmlRootElement.class) != null && mediaType.equals(MediaType.APPLICATION_XML_TYPE);
    }

    @Override
    public long getSize(Object t, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
        return -1;
    }

    @Override
    public void writeTo(Object t, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException,
            WebApplicationException {
        Locale locale = If.first(this.requestHeaders.getAcceptableLanguages(), Locale.US);
        NumberFormat formatter = NumberFormat.getNumberInstance(locale);
        formatter.setMaximumFractionDigits(1);

        Marshaller marshaller;
        try {
            JAXBContext jc = JAXBContext.newInstance(TrackInfo.class);
            marshaller = jc.createMarshaller();
            marshaller.setAdapter(QuantityXmlAdapter.class, new QuantityXmlAdapter.Builder().locale(locale).build());
            marshaller.setAdapter(NumberPersonalizedXmlAdapter.class, new NumberPersonalizedXmlAdapter.Builder()
                    .formatter(formatter).build());

            marshaller.marshal(t, entityStream);
        } catch (JAXBException e) {
            throw new RuntimeException(e);
        }
    }
}

使用默认语言环境en-US生成此xml摘录：

 <display lang="en_US">
    <value>3,286.1</value>
 </display>

以及在标题中发送fr-FR的语言环境时的此xml摘录：

 <display lang="fr_FR">
   <value>3 286,1</value>
 </display>

这种方法仍然不理想，因为我现在需要为JSON编写类似的MessageBodyWriter或为此MessageBodyWriter添加JSON支持。另外我假设默认的JAXB提供程序正在做一些我没有利用的调整。

Answer 3

MessageBodyWriter是此用例的正确方法。我建议您将以下字段添加到MessageBodyWriter：

@javax.ws.rs.core.Context
protected Providers providers;

然后使用它来访问JAXBContext以创建Marshaller

public void writeTo(DataObject dataObject, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> multivaluedMap, OutputStream outputStream) throws IOException, WebApplicationException {
    JAXBContext jaxbContext = null;
    ContextResolver<JAXBContext> resolver = providers.getContextResolver(JAXBContext.class, arg3);
    if(null != resolver) {
        jaxbContext = resolver.getContext(type);
    }
    if(null == jaxbContext) {
        jaxbContext = JAXBContext.newInstance(type);
    }
    Marshaller marshaller = jaxbContext.createMarshaller();
}

相关示例

Validate JAXBElement in JPA/JAX-RS Web Service

我如何i18n JAX-RS（泽西岛）JAXB注释响应

3 个答案: