How do I use the Jersey JSON POJO support?

Question

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

Answer 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();
}

Answer 2

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>

Answer 3

Why are you using final fields? I'm using jersey and i have some JAXB objects/pojos and all i had to do was simply annotate my resource method with @Produces("application/json") and it works out of the box. I didn't have to mess with the web.xml. Just make sure your pojos are annotated correctly.

Here is a simple pojo

package test;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class SampleJaxbObject {

    private String field1;

    private Integer field2;

    private String field3;

    public String getField1() {
        return field1;
    }

    public void setField1(String field1) {
        this.field1 = field1;
    }

    public Integer getField2() {
        return field2;
    }

    public void setField2(Integer field2) {
        this.field2 = field2;
    }

    public String getField3() {
        return field3;
    }

    public void setField3(String field3) {
        this.field3 = field3;
    }


}

Answer 4

You've probably already figured this out, but all you need to do is add these jackson jars to your classpath: jackson-core, jackson-jaxrs, jackson-mapper, and jackson-xc

It appears that there is another way, as others have noted. Add this to your "com.sun.jersey.config.property.packages" parameter (if using tomcat and web.xml): "org.codehaus.jackson.jaxrs", like so:

<init-param>
  <param-name>com.sun.jersey.config.property.packages</param-name>
  <param-value>org.codehaus.jackson.jaxrs</param- value>
</init-param>

Doing this will also require the same jackson jars on your classpath