使用JAXB在Jersey RESTful API的JSON输出中包含null元素 [英] Including null elements in JSON output of Jersey RESTful API with JAXB
问题描述
我有一个类，我想通过Jersey RESTful API公开。它看起来类似于：
I have a class that I would like to expose through a Jersey RESTful API. It looks similar to this:
@XmlRootElement
public class Data {
public String firstName;
public String lastName;
}
我的问题是这些字段可能为空，在这种情况下字段是从JSON输出中省略。我希望所有领域都存在，无论它们的价值如何。例如，如果lastName为null，则JSON输出将为：
My problem is that these fields may be null, in which case the field is omitted from the JSON output. I would like all fields to be present regardless of their value. For example, if lastName is null, the JSON output will be:
{
"firstName" : "Oleksi"
}
而不是我想要的：
{
"firstName" : "Oleksi",
"lastName" : null
}
我有一个JAXBContextResolver（ContextResolver的实现），如下所示：
I have a JAXBContextResolver (an implementation of ContextResolver) that looks like this:
@Provider
public class JAXBContextResolver implements ContextResolver<JAXBContext> {
// internal state
private final JAXBContext context;
private final Set<Class> types;
private final Class[] cTypes = { Data.class };
public JAXBContextResolver()
throws Exception {
types = new HashSet(Arrays.asList(cTypes));
context = new JSONJAXBContext(JSONConfiguration.natural().humanReadableFormatting(true).build(), cTypes);
}
@Override
public JAXBContext getContext(Class<?> objectType) {
return (types.contains(objectType)) ? context : null;
}
}
我一直试图找出如何获得那个期望的输出一段时间，但我没有运气。我愿意尝试其他ContextResolvers / Serializers，但我找不到一个有效的代码示例，所以代码示例会很好。
I've been trying to figure out how to get that desired output for a while, but I've had no luck. I'm open to trying other ContextResolvers/Serializers, but I haven't been able to find one that works, so code examples would be nice.
推荐答案
对于 EclipseLink JAXB（MOXy） 的JSON绑定，正确的映射如下。您可以尝试与您的提供商一起查看它是否也可以使用：
For EclipseLink JAXB (MOXy)'s JSON binding, the correct mapping would be the following. You could try it with your provider to see if it would work also:
@XmlRootElement
public class Data {
@XmlElement(nillable=true)
public String firstName;
@XmlElement(nillable=true)
public String lastName;
}
更多信息
- http://blog.bdoughan.com/2012/04/binding-to-json-xml-handling-null.html
- http://blog.bdoughan.com/2012/05/moxy-as-your-jax- rs-json-provider.html
- http://blog.bdoughan.com/2012/04/binding-to-json-xml-handling-null.html
- http://blog.bdoughan.com/2012/05/moxy-as-your-jax-rs-json-provider.html
更新2
EclipseLink 2.4包含 MOXyJsonProvider 这是 MessageBodyReader <的实现/ code> / MessageBodyWriter 您可以直接使用MOXy的JSON绑定
EclipseLink 2.4 includes MOXyJsonProvider which is an implementation of MessageBodyReader/MessageBodyWriter that you can use directly to leverage MOXy's JSON binding
- http://blog.bdoughan.com/2012/05/moxy-as-your-jax-rs-json-provider.html
更新1
关注 MessageBodyReader / MessageBodyWriter 可能更适合您：
The following MessageBodyReader/MessageBodyWriter may work better for you:
import java.io.*;
import java.lang.annotation.Annotation;
import java.lang.reflect.*;
import javax.xml.transform.stream.StreamSource;
import javax.ws.rs.*;
import javax.ws.rs.core.*;
import javax.ws.rs.ext.*;
import javax.xml.bind.*;
import org.eclipse.persistence.jaxb.JAXBContextFactory;
@Provider
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public class MOXyJSONProvider implements
MessageBodyReader<Object>, MessageBodyWriter<Object>{
@Context
protected Providers providers;
public boolean isReadable(Class<?> type, Type genericType,
Annotation[] annotations, MediaType mediaType) {
return true;
}
public Object readFrom(Class<Object> type, Type genericType,
Annotation[] annotations, MediaType mediaType,
MultivaluedMap<String, String> httpHeaders, InputStream entityStream)
throws IOException, WebApplicationException {
try {
Class<?> domainClass = getDomainClass(genericType);
Unmarshaller u = getJAXBContext(domainClass, mediaType).createUnmarshaller();
u.setProperty("eclipselink.media-type", mediaType.toString());
u.setProperty("eclipselink.json.include-root", false);
return u.unmarshal(new StreamSource(entityStream), domainClass).getValue();
} catch(JAXBException jaxbException) {
throw new WebApplicationException(jaxbException);
}
}
public boolean isWriteable(Class<?> type, Type genericType,
Annotation[] annotations, MediaType mediaType) {
return true;
}
public void writeTo(Object object, Class<?> type, Type genericType,
Annotation[] annotations, MediaType mediaType,
MultivaluedMap<String, Object> httpHeaders,
OutputStream entityStream) throws IOException,
WebApplicationException {
try {
Class<?> domainClass = getDomainClass(genericType);
Marshaller m = getJAXBContext(domainClass, mediaType).createMarshaller();
m.setProperty("eclipselink.media-type", mediaType.toString());
m.setProperty("eclipselink.json.include-root", false);
m.marshal(object, entityStream);
} catch(JAXBException jaxbException) {
throw new WebApplicationException(jaxbException);
}
}
public long getSize(Object t, Class<?> type, Type genericType,
Annotation[] annotations, MediaType mediaType) {
return -1;
}
private JAXBContext getJAXBContext(Class<?> type, MediaType mediaType)
throws JAXBException {
ContextResolver<JAXBContext> resolver
= providers.getContextResolver(JAXBContext.class, mediaType);
JAXBContext jaxbContext;
if(null == resolver || null == (jaxbContext = resolver.getContext(type))) {
return JAXBContextFactory.createContext(new Class[] {type}, null);
} else {
return jaxbContext;
}
}
private Class<?> getDomainClass(Type genericType) {
if(genericType instanceof Class) {
return (Class<?>) genericType;
} else if(genericType instanceof ParameterizedType) {
return (Class<?>) ((ParameterizedType) genericType).getActualTypeArguments()[0];
} else {
return null;
}
}
}
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