List data in a datatable

Question

I believe this method of dao that should not be correct.

DAO METHOD

public List <Campeonato> listarTodos() {

        try {
            manager.getTransaction().begin();
            Query query = manager.createNamedQuery("Campeonato.listarTodos", Campeonato.class);
            @SuppressWarnings("unchecked")
            List <Campeonato> campeonatos = query.getResultList();
            for (Campeonato campeonato : campeonatos) {
                campeonato.setId(campeonato.getId());
                campeonato.setNome(campeonato.getNome());
                campeonatos.add(campeonato);
                Iterator <Campeonato> iterator = campeonatos.iterator();
            while (iterator.hasNext()) {
                campeonato = iterator.next();
                }
            } 
            return campeonatos;
        } finally {
            manager.close();
        }
    }

MY BEAN

import java.util.List;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;

import dao.CampeonatoDao;

import model.Campeonato;

@ManagedBean
@RequestScoped
public class CampeonatoBean {

    private Campeonato campeonato;
    private List <Campeonato> campeonatos;

    public CampeonatoBean() {

        campeonato = new Campeonato();
    }
    public void salvar() throws Exception {

        CampeonatoDao campeonatoDao = new CampeonatoDao();
        campeonatoDao.salvar(campeonato);
    }

    public void deletar() throws Exception {

        CampeonatoDao campeonatoDao = new CampeonatoDao();
        campeonatoDao.deletar(campeonato);
    }

    public List <Campeonato> listarCampeonatos()  {

        CampeonatoDao campeonatoDao = new CampeonatoDao();
         campeonatos = campeonatoDao.listarTodos();
         return campeonatos;
    }

    public Campeonato getCampeonato() {
        return campeonato;
    }

    public void setCampeonato(Campeonato campeonato) {
        this.campeonato = campeonato;
    }

    public List<Campeonato> getCampeonatos() {
        return campeonatos;
    }

    public void setCampeonatos(List<Campeonato> campeonatos) {
        this.campeonatos = campeonatos;
    }
}

XHTML

<h:form> 
<p:fieldset> <br/>

<p:panelGrid columns="3" > 
<p:outputLabel value="CAMPEONATO: " /> 
<p:inputText  value="#{campeonatoBean.campeonato.nome}" />
<p:commandButton ajax="false" value="SALVAR" action="#{campeonatoBean.salvar}"/>
</p:panelGrid> <br/>

<p:commandButton ajax="false" value="LISTAR" action="#{campeonatoBean.listarCampeonatos}" />

<p:dataTable value="#{campeonatoBean.campeonatos}" var="campeonato" resizableColumns="true" >
<f:facet name="header">
<p:outputLabel value="LISTA DE CAMPEONATOS" />
</f:facet>
<p:column headerText="ID" sortBy="#{campeonato.id}" >
<h:outputText value="#{campeonato.id}" />
</p:column>     
<p:column headerText="CAMPEONATO" sortBy="#{campeonato.nome}" >
<h:outputText value="#{campeonato.nome}" />
</p:column>     
<p:column >
<p:commandButton ajax="false" value="EXCLUIR" action="#{campeonatoBean}"/>          
</p:column>
</p:dataTable>

</p:fieldset>
</h:form>   

ERROR

Type Exception Report

Message java.util.ConcurrentModificationException

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

javax.servlet.ServletException: java.util.ConcurrentModificationException
  javax.faces.webapp.FacesServlet.service(FacesServlet.java:671)
  org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

Root Cause

javax.faces.el.EvaluationException: java.util.ConcurrentModificationException
  javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:101)
  com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
  javax.faces.component.UICommand.broadcast(UICommand.java:315)
  javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:790)
  javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1282)
  com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
  com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
  com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
  javax.faces.webapp.FacesServlet.service(FacesServlet.java:658)
  org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)

Root Cause

java.util.ConcurrentModificationException
  java.util.ArrayList$Itr.checkForComodification(Unknown Source)
  java.util.ArrayList$Itr.next(Unknown Source)
  dao.CampeonatoDao.listarTodos(CampeonatoDao.java:62)
  controller.CampeonatoBean.listarCampeonatos(CampeonatoBean.java:38)
  sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
  sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
  java.lang.reflect.Method.invoke(Unknown Source)
  org.apache.el.parser.AstValue.invoke(AstValue.java:247)
  org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:267)
  com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
  javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:87)
  com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
  javax.faces.component.UICommand.broadcast(UICommand.java:315)
  javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:790)
  javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1282)
  com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
  com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
  com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:198)
  javax.faces.webapp.FacesServlet.service(FacesServlet.java:658)
  org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
Note The full stack trace of the root cause is available in the server logs.

Answer 1

The reported error is the exception ConcurrentModificationException, which according to the documentation, in free translation:

This exception can be made by methods that detected the modification simultaneous of an object when such modification is not permitted.

that is, you are changing an object Campeonato which is contained in the list campeonatos, in the method listarTodos.

For the result waiting for the list returned by getResultList() is enough, would be:

public List <Campeonato> listarTodos() {
    try {
        manager.getTransaction().begin();
        Query query = manager.createNamedQuery("Campeonato.listarTodos", Campeonato.class);
        return query.getResultList();
    } finally {
        manager.close();
    }
}