GET request fails with JAX-RS: Could not find MessageBodyWriter for response object of type: java.util.ArrayList of media type: text/html

Question

I'm building a sample client-server with JAX-RS using JEE7. I'm using Wildfly 10.1

I followed the guy in this video. Here is the code of the war that runs on the application server:

boundary package contains the service

package pl.devcrowd.virtual.business.chickens.boundary;

import java.util.List;

import javax.ejb.Stateless;
import javax.inject.Inject;

import pl.devcrowd.virtual.business.chickens.controls.ChickenStore;
import pl.devcrowd.virtual.business.chickens.entity.Chicken;

@Stateless
public class ChickenService {

    @Inject
    ChickenStore cs;

    public List<Chicken> getAllChickens() {
        return this.cs.all();
    }

    public void save(Chicken chicken) {
        this.cs.save(chicken);
    }
}

and the resource

package pl.devcrowd.virtual.business.chickens.boundary;

import java.util.List;

import javax.inject.Inject;
import javax.json.JsonObject;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;

import pl.devcrowd.virtual.business.chickens.entity.Chicken;

@Path("chickens")
public class ChickensResource {

    @Inject
    ChickenService cs;

    @GET
    public List<Chicken> chickens() {
        return cs.getAllChickens();
    }

    @POST
    public void save(JsonObject chicken) {
        String name = chicken.getString("name");
        int age = chicken.getInt("age");
        cs.save(new Chicken(name, age));
    }
}

control package contains the store which is mostly useless in this example

package pl.devcrowd.virtual.business.chickens.controls;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import pl.devcrowd.virtual.business.chickens.entity.Chicken;

public class ChickenStore {

    @PersistenceContext
    EntityManager em;

    public void save(Chicken chicken) {
        em.merge(chicken);
    }

    public List<Chicken> all() {
        return this.em
                .createNamedQuery("all", Chicken.class)
                .getResultList();
    }
}

entity package contains the entity:

package pl.devcrowd.virtual.business.chickens.entity;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.NamedQuery;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlRootElement;

@XmlAccessorType(XmlAccessType.FIELD)
@XmlRootElement
@Entity
@NamedQuery(name="all", query = "SELECT c FROM Chicken C")
public class Chicken {

    @Id
    @GeneratedValue
    private long id;
    private String name;
    private int age;

    public Chicken() {}

    public Chicken(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

The parent package contains the Jax-RS application class which I implemented, I hope correctly:

package pl.devcrowd.virtual.business;

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;

import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;

import pl.devcrowd.virtual.business.chickens.boundary.ChickensResource;

/**
 * Configures a JAX-RS endpoint. Delete this class, if you are not exposing
 * JAX-RS resources in your application.
 *
 * @author airhacks.com
 */
@ApplicationPath("resources")
public class JAXRSConfiguration extends Application {
    public Set<Class<?>> getClasses() {
        return new HashSet<Class<?>>(Arrays.asList(ChickensResource.class));
    }
}

Now i'm trying to do a GET request like this

RestClient get = RestClient.create().method("GET")
        .host("http://localhost:8080/DevCrowd")
        .path("resources/chickens");
GluonObservableList<Chicken> sample = DataProvider.retrieveList(
        get.createListDataReader(Chicken.class));
System.out.println(sample);

where Chicken is

public class Chicken {

    private String name;
    private int age;

    public Chicken(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

and I get the error:

05:59:17,019 ERROR [org.jboss.resteasy.resteasy_jaxrs.i18n] (default task-3) RESTEASY002005: Failed executing GET /chickens: org.jboss.resteasy.core.NoMessageBodyWriterFoundFailure: Could not find MessageBodyWriter for response object of type: java.util.ArrayList of media type: text/html
    at org.jboss.resteasy.core.ServerResponseWriter.writeNomapResponse(ServerResponseWriter.java:66)
    at org.jboss.resteasy.core.SynchronousDispatcher.writeResponse(SynchronousDispatcher.java:473)
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:422)
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:209)
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:221)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
    at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
    at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
    at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81)
    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138)
    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135)
    at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
    at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44)
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104)
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202)
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:805)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

What am I doing wrong?

Tobias Grott · Accepted Answer · 2017-05-08T18:17:17.707

As far as I see the client calls for mediatype text/html. But the objectmapper does not know how to write html for an arraylist. What kind of format do you expect xml or json?

@Path("chickens")
public class ChickensResource {

    @Inject
    ChickenService cs;

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public List<Chicken> chickens() {
        return cs.getAllChickens();
    }

    @POST
    @Consumes(MediaType.APPLICATION_JSON)
    @Produces(MediaType.APPLICATION_JSON)
    public void save(JsonObject chicken) {
        String name = chicken.getString("name");
        int age = chicken.getInt("age");
        cs.save(new Chicken(name, age));
    }
}

An other solution would be to set the right requested Content type in the Request: GET Header:

 Accept: application/json

POST Header:

Accept: application/json
Content-Type: application/json

The Accept header says in which format the response should be. The Content-Type header says which format the request payload has.

Content Types:

HTML --> text/html
JSON --> application/json
XML --> application/xml

edit: I think the Post has the same issue. We now told the methods that they consume json as input data and return json as output data (produces).

But are those data really set in the request. can you please post how you construct the post.

To match those methods there need to be those two headers in the request: Accept: application/json says which format the client expects. This should match the @Produces in the service which sets the output format. Content-Type: application/json this is the one I think is missing says in which format the POST payload is and this should match the server input @Consumes

I added the `@Consumes` and `@Produces`. GET works now and I get an empty list `[]` like I should! Thanks! Now i have a problem with POST: `Failed to execute: javax.ws.rs.NotSupportedException: RESTEASY003065: Cannot consume content type`. I can ask a new question about POST because this one was about getting GET to work, but do you have an idea where the problem is? Client or server? I understand what the error means, not why is happens or how to fix it. — Mark, May 07 '17 at 16:45

GET request fails with JAX-RS: Could not find MessageBodyWriter for response object of type: java.util.ArrayList of media type: text/html

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