未找到 Media type=text/plain、type=class java.util.ArrayList、genericType=java.util.List 的 MessageBodyWriter<models.Person>

Question

I have written a jersey REST API method which returns a list of persons which is queried from mysql backend using hibernate. Here is the method

    @Path("Person")
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public List<Person> person()
    {
        SessionFactory sessionFactory = new Configuration().configure().buildSessionFactory();
        Session session = sessionFactory.openSession();
        Transaction tx = session.beginTransaction();
        Criteria cr = session.createCriteria(Person.class);
        List persons =  cr.list();
        GenericEntity<List<Person>> list = new GenericEntity<List<Person>>(persons) {};
        tx.commit();
        session.close();
        return persons;

    }

and here is my MessageBodyWriter

@Provider
@Produces(MediaType.APPLICATION_JSON)
public class PersonMessageBodyWriter implements MessageBodyWriter<Person> {

@Override
public long getSize(Person arg0, Class<?> arg1, Type arg2, Annotation[] arg3, MediaType arg4) {
    // TODO Auto-generated method stub
    return -1;
}

@Override
public boolean isWriteable(Class<?> type, Type arg1, Annotation[] arg2, MediaType arg3) {
    return Person.class.isAssignableFrom(type);
}

@Override
public void writeTo(Person person, Class<?> type, Type type1, Annotation[] arg3, MediaType arg4,
        MultivaluedMap<String, Object> arg5, OutputStream out) throws IOException, WebApplicationException {
    // TODO Auto-generated method stub
        out.write(person.toString().getBytes());
    }

}

When i make a get request to the above method i am getting SEVERE: MessageBodyWriter not found for media type=text/plain, type=class java.util.ArrayList, genericType=java.util.List. can someone please help me get through with this problem?

Answer 1

What I've always done in this case is make a Persons object that contains the List of persons. There may be a better way but if your under a time crunch and want to get it done then this should work. If it doesn't work then my guess that no JSON marshalling is working, in which case you have a configuration problem.

import java.util.ArrayList;
import java.util.List;

public class Persons
{
    private List<Person> persons = new ArrayList<>();

    public List<Person> getPersons()
    {
        return persons;
    }

    public void setPersons(List<Person> persons)
    {
        this.persons = persons;
    }
}

Answer 2

I understand that this is quite an old question - However, there is an excellent solution to this now. Whenever you wish to return a list of objects, you can utilise the below code:

List<KaggleFileResponse> data = kaggleService.listFiles(xxxx);
GenericEntity<List<KaggleFileResponse>> entity = new GenericEntity<List<KaggleFileResponse>>(data) {};
return Response.status(HttpStatus.SC_OK).entity(entity).build();

The code converts the list into a generic entity that can be written back.