How do I i18n JAX-RS (Jersey) JAXB注释响应

Question

我们在从Web API返回的模型对象上使用JAXB注释，我们希望数据本地化，并根据用户偏好设置其他值的格式(例如，指标与法规)。我们通过向Marshaller添加自定义适配器来实现这一点。

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

尝试最简单的方法，我将只从HTTP请求头部获取区域设置，并将其提供给其中一个MessageBodyWriter类中的Marshaller。

我考虑过扩展像XMLRootElementProvider这样的默认注册提供者，但意识到它们大多是最终版本，所以我放弃了这种方法。无论如何，我至少需要扩展10个类，所以这并不理想。

有人知道如何最好地让MessageBodyWriter中的编组程序为每个请求设置customer Adapter吗？我很确定这和ContextResolver有关。

Answer 1

与编写MessageBodyWriter相比，为编组编写ContextResolver会产生更干净、更合适的解决方案。所有JAXB类都使用Providers.getContextResolver方法来获取编组程序。我提供了我的自定义ContextResolver，并且我有i18n响应。

@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没有本地化，在一些调查之后，我意识到使用Jackson JSON库而不是与Jersey库一起分发的JAXBJSONElementProvider。I removed the POJOMappingFeature configuration in web.xml，我已经本地化了JSON，然而，它不如Jackson JSON好。

一个非常干净的解决方案，这让我认为JAX-RS和Jersey实现做得非常好。

Answer 2

我通过编写自己的MessageBodyWriter解决了这个问题，它接收注入到构造函数中的HttpHeaders，我稍后编写响应时会用到该构造函数。我将包括整个类，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);
        }
    }
}

它使用默认语言环境en-US生成以下xml摘录：

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

以及在报头中发送fr-FR的区域设置时的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编写一个类似的MessageBodyWriter，或者在这个MessageBodyWriter中添加对JSON的支持。此外，我假设默认的JAXB提供程序正在进行一些我没有利用的调整。

Answer 3

对于这种用例，MessageBodyWriter是正确的方法。我建议在您的MessageBodyWriter中添加以下字段

@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();
}

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