How do I use the Jersey JSON POJO support?
I have an object that I'd like to serve in JSON as a RESTful resource. I have Jersey's JSON POJO support turned on like so (in web.xml):
<servlet>
<servlet-name>Jersey Web Application</servlet-name>
<servlet-class>com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>
<init-param>
<param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name>
<param-value>true</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
But when I try to access the resource, I get this exception:
SEVERE: A message body writer for Java type, class com.example.MyDto, and MIME media type, application/json, was not found
SEVERE: Mapped exception to response: 500 (Internal Server Error)
javax.ws.rs.WebApplicationException
...
The class that I'm trying to serve isn't complicated, all it's got are some public final fields and a constructor that sets all of them. The fields are all strings, primitives, classes similar to this one, or Lists thereof (I've tried using plain Lists instead of generic List<T>s, to no avail). Does anyone know what gives? Thanks!
Java EE 6
Jersey 1.1.5
GlassFish 3.0.1
Jersey-json has a JAXB implementation. The reason you're getting that exception is because you don't have a Provider registered, or more specifically a MessageBodyWriter. You need to register a proper context within your provider:
@Provider
public class JAXBContextResolver implements ContextResolver<JAXBContext> {
private final static String ENTITY_PACKAGE = "package.goes.here";
private final static JAXBContext context;
static {
try {
context = new JAXBContextAdapter(new JSONJAXBContext(JSONConfiguration.mapped().rootUnwrapping(false).build(), ENTITY_PACKAGE));
} catch (final JAXBException ex) {
throw new IllegalStateException("Could not resolve JAXBContext.", ex);
}
}
public JAXBContext getContext(final Class<?> type) {
try {
if (type.getPackage().getName().contains(ENTITY_PACKAGE)) {
return context;
}
} catch (final Exception ex) {
// trap, just return null
}
return null;
}
public static final class JAXBContextAdapter extends JAXBContext {
private final JAXBContext context;
public JAXBContextAdapter(final JAXBContext context) {
this.context = context;
}
@Override
public Marshaller createMarshaller() {
Marshaller marshaller = null;
try {
marshaller = context.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
} catch (final PropertyException pe) {
return marshaller;
} catch (final JAXBException jbe) {
return null;
}
return marshaller;
}
@Override
public Unmarshaller createUnmarshaller() throws JAXBException {
final Unmarshaller unmarshaller = context.createUnmarshaller();
unmarshaller.setEventHandler(new DefaultValidationEventHandler());
return unmarshaller;
}
@Override
public Validator createValidator() throws JAXBException {
return context.createValidator();
}
}
}
This looks up for an @XmlRegistry within the provided package name, which is a package that contains @XmlRootElement annotated POJOs.
@XmlRootElement
public class Person {
private String firstName;
//getters and setters, etc.
}
then create an ObjectFactory in the same package:
@XmlRegistry
public class ObjectFactory {
public Person createNewPerson() {
return new Person();
}
}
With the @Provider registered, Jersey should facilitate the marshalling for you in your resource:
@GET
@Consumes(MediaType.APPLICATION_JSON)
public Response doWork(Person person) {
// do work
return Response.ok().build();
}
You can use @XmlRootElement if you want to use JAXB annotations (see other answers).
However, if you prefer pure POJO mapping, you must do the following (Unfortunately it isn't written in docs):
com.sun.jersey.config.property.packages init parameter, add org.codehaus.jackson.jaxrs to the list. This will include JSON providers in the scan list of Jersey. This did it for me - Jersey 2.3.1
In the web.xml file :
<servlet>
<servlet-name>Jersey Web Application</servlet-name>
<servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
<init-param>
<param-name>jersey.config.server.provider.packages</param-name>
<param-value><my webapp packages>;org.codehaus.jackson.jaxrs</param-value>
</init-param>
</servlet>
In the pom.xml file :
<dependency>
<groupId>org.glassfish.jersey.media</groupId>
<artifactId>jersey-media-json-jackson</artifactId>
<version>2.3.1</version>
</dependency>