[英]Including null elements in JSON output of Jersey RESTful API with JAXB
我有一個類,我想通過Jersey RESTful API公開。 它看起來類似於:
@XmlRootElement
public class Data {
public String firstName;
public String lastName;
}
我的問題是這些字段可能為null,在這種情況下,字段從JSON輸出中省略。 我希望所有領域都存在,無論它們的價值如何。 例如,如果lastName為null,則JSON輸出將為:
{
"firstName" : "Oleksi"
}
而不是我想要的:
{
"firstName" : "Oleksi",
"lastName" : null
}
我有一個JAXBContextResolver(ContextResolver的實現),如下所示:
@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;
}
}
我一直試圖弄清楚如何在一段時間內獲得所需的輸出,但我沒有運氣。 我願意嘗試其他ContextResolvers / Serializers,但我找不到一個有效的代碼示例,所以代碼示例會很好。
對於EclipseLink JAXB(MOXy)的JSON綁定,正確的映射如下。 您可以嘗試與您的提供商一起查看它是否也可以:
@XmlRootElement
public class Data {
@XmlElement(nillable=true)
public String firstName;
@XmlElement(nillable=true)
public String lastName;
}
欲獲得更多信息
更新2
EclipseLink 2.4包含MOXyJsonProvider
,它是MessageBodyReader
/ MessageBodyWriter
一個實現,您可以直接使用它來利用MOXy的JSON綁定
更新1
以下MessageBodyReader
/ MessageBodyWriter
可能更適合您:
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;
}
}
}
Java null是JavaScript未定義的。 如果要將Java null轉換為JavaScript null,則需要查閱轉換庫。
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