Deployment of PersistenceUnit [...] failed. Close all factories for this PersistenceUnit

Question

I keep getting this error when calling hentMeldinger();

public class Kontroll {
    private EntityManagerFactory emf;

    Kontroll() {
        emf = Persistence.createEntityManagerFactory("meldingsTing");
    }

    public List<Melding> hentMeldinger() {
        EntityManager em = emf.createEntityManager();

        TypedQuery<Melding> query = em.createQuery("SELECT o FROM Melding o",
        Melding.class);// FIKS
        List<Melding> meldinger = query.getResultList();

        em.close();

        return meldinger;
    }
}

The Exception Report:

message Exception [EclipseLink-28019] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.persistence.PersistenceException: Exception [EclipseLink-28019] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Deployment of PersistenceUnit [meldingsTing] failed. Close all factories for this PersistenceUnit.
Internal Exception: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions: 
---------------------------------------------------------

Exception [EclipseLink-63] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The instance creation method [no.hib.dat104.oblig1.Melding.<Default Constructor>], with no parameters, does not exist, or is not accessible.
Internal Exception: java.lang.NoSuchMethodException: no.hib.dat104.oblig1.Melding.<init>()
Descriptor: RelationalDescriptor(no.hib.dat104.oblig1.Melding --> [DatabaseTable(MELDING)])

Runtime Exceptions: 
---------------------------------------------------------

    org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.createDeployFailedPersistenceException(EntityManagerSetupImpl.java:820)
    org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:760)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.getAbstractSession(EntityManagerFactoryDelegate.java:204)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.createEntityManagerImpl(EntityManagerFactoryDelegate.java:304)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:336)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:302)
    no.hib.dat104.oblig1.Kontroll.lagreMelding(Kontroll.java:32)
    no.hib.dat104.oblig1.MeldingServlet.doPost(MeldingServlet.java:83)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

Root Cause:

Exception [EclipseLink-28019] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Deployment of PersistenceUnit [meldingsTing] failed. Close all factories for this PersistenceUnit.
Internal Exception: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions: 
---------------------------------------------------------

Exception [EclipseLink-63] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The instance creation method [no.hib.dat104.oblig1.Melding.<Default Constructor>], with no parameters, does not exist, or is not accessible.
Internal Exception: java.lang.NoSuchMethodException: no.hib.dat104.oblig1.Melding.<init>()
Descriptor: RelationalDescriptor(no.hib.dat104.oblig1.Melding --> [DatabaseTable(MELDING)])

Runtime Exceptions: 
---------------------------------------------------------

    org.eclipse.persistence.exceptions.EntityManagerSetupException.deployFailed(EntityManagerSetupException.java:238)
    org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.createDeployFailedPersistenceException(EntityManagerSetupImpl.java:820)
    org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:760)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.getAbstractSession(EntityManagerFactoryDelegate.java:204)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.createEntityManagerImpl(EntityManagerFactoryDelegate.java:304)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:336)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:302)
    no.hib.dat104.oblig1.Kontroll.lagreMelding(Kontroll.java:32)
    no.hib.dat104.oblig1.MeldingServlet.doPost(MeldingServlet.java:83)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions: 
---------------------------------------------------------

Exception [EclipseLink-63] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The instance creation method [no.hib.dat104.oblig1.Melding.<Default Constructor>], with no parameters, does not exist, or is not accessible.
Internal Exception: java.lang.NoSuchMethodException: no.hib.dat104.oblig1.Melding.<init>()
Descriptor: RelationalDescriptor(no.hib.dat104.oblig1.Melding --> [DatabaseTable(MELDING)])

Runtime Exceptions: 
---------------------------------------------------------

    org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:696)
    org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:632)
    org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:568)
    org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.postConnectDatasource(DatabaseSessionImpl.java:799)
    org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.loginAndDetectDatasource(DatabaseSessionImpl.java:743)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryProvider.login(EntityManagerFactoryProvider.java:239)
    org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:685)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.getAbstractSession(EntityManagerFactoryDelegate.java:204)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryDelegate.createEntityManagerImpl(EntityManagerFactoryDelegate.java:304)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:336)
    org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:302)
    no.hib.dat104.oblig1.Kontroll.lagreMelding(Kontroll.java:32)
    no.hib.dat104.oblig1.MeldingServlet.doPost(MeldingServlet.java:83)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

My problem is that I have no idea where to start when looking at this error report. I've tried for a couple of hours now, but it makes no sense to me. Would be awesome if anyone could make som sense out of it and explain, but resolving the problem would be the best.

Answer 1

Exception Description: The instance creation method [no.hib.dat104.oblig1.Melding.<Default Constructor>], with no parameters, does not exist, or is not accessible.

For JPA entity, at least must include default constructor (no-arg constructor),

public Melding() {
}