JSF 2: A NullPointerException hits an unexpected managed bean at submission

Question

Hello,
What a strange trouble I am facing today (I am still a newbie with JSF).
I have this web page:
<ui:composition template="/web/authentification/login/cnam/layout_cnam.xhtml">
      <ui:define name="content">
       <devoir:formulaireDeRemise sujetExamen="${devoirRemis.sujetExamen}" idAuditeur="${devoirRemis.auditeurId}" locale="${devoirRemis.requestLocale}" />
      </ui:define>
   </ui:composition>it uses composites, and composites that use composites, and the whole page and its composites rely on a Managed Bean, DevoirRemisBean:
@ManagedBean(name="devoirRemis") @RequestScoped
public class DevoirRemisBean extends BaseManagedBean
private static Logger log = Logger.getLogger(DevoirRemisBean.class);
private AuditeurId m_idAuditeur;
private SujetExamen m_sujetExamen;
private CorrecteurFacade m_correcteurService = CorrecteurFacade.getInstance(getRequestLocale());
private EnseignantFacade m_enseignementService = EnseignantFacade.getInstance(getRequestLocale());
   public DevoirRemisBean()
      log.debug("DevoirRemisBean {0} créé.", this);
   public String doPréparerRemise(AuditeurId idAuditeur, UVId idUV, SujetId idSujet)
      assert(idAuditeur != null) : "L'identifiant de l'auditeur remettant un devoir ne peut pas valoir null.";
      assert(idUV != null) : "L'identifiant de l'UE du devoir à remettre ne peut pas valoir null.";
      assert(idSujet != null) : "L'identifiant du sujet d'examen pour le devoir à remettre ne peut pas valoir null.";
      m_idAuditeur = idAuditeur;
      m_sujetExamen = getSujetExamen(idUV, idSujet);
      log.debug("DevoirRemisBean {0} associé au casier ({1},{2},{3}).", this, idAuditeur, idUV, idSujet);
      return(destination(REMISE_DEVOIR_CNAM));
  // others getters and setters...
  // Eventually each getter always call this check() method to ensure being in a good state.
   public void check()
      assert(m_idAuditeur != null) : format("L''identifiant de l''auditeur devrait être connu à l''issue de la préparation de la remise de devoir, bean: {0}.", this);
      assert(m_sujetExamen != null)  : format("Le sujet d''examen devrait être connu à l''issue de la préparation de la remise de devoir, bean: {0}.", this);
   }When the interesting composite is called,
<devoir:formulaireDeRemise sujetExamen="${devoirRemis.sujetExamen}" idAuditeur="${devoirRemis.auditeurId}" locale="${devoirRemis.requestLocale}" />
it produces the expected result on the web page,
I can see in my logs these lines, that makes me happy:
DevoirRemisBean tag.uv.DevoirRemisBean@1133ead créé.
DevoirRemisBean tag.uv.DevoirRemisBean@1133ead associé au casier (I023895,X1,TP03).
meaning that the expected values are at the place I want them to be.
In the web page displayed, a new submit button now exists.
<h:inputHidden name="idAuditeur" value="${devoirRemis.auditeurId}" />
<h:inputHidden name="idUV" value="${devoirRemis.sujetExamen.UV.id}" />
<h:inputHidden name="idSujet" value="${devoirRemis.sujetExamen.id}" />
<h:commandButton action="#{correction.doCorrection(idAuditeur, idUV, idSujet)}"
   styleClass="BtnVertNonPresse" value="${lblFormRemise.btn_envoyer}"
   onmousedown="if (this.className != 'BtnVertPresse') this.className='BtnVertPresse';"
   onmouseout="if (this.className != 'BtnVertNonPresse') this.className='BtnVertNonPresse';"
   onmouseup="if (this.className != 'BtnVertNonPresse') this.className='BtnVertNonPresse';" />(I have added <h:inputHidden> fields, for debugging.)
This button is linked to an action that shall use another managed bean, correction, starting the same way than the other.
@ManagedBean(name="correction") @RequestScoped
public class DevoirCorrigéBean extends BaseManagedBean
private static Logger log = Logger.getLogger(DevoirCorrigéBean.class);
private AuditeurId m_idAuditeur;
private SujetExamen m_sujetExamen;
   public DevoirCorrigéBean()
      log.debug("DevoirCorrigéBean {0} créé.", this);
   public String doCorrection(AuditeurId idAuditeur, UVId idUV, SujetId idSujet)
      assert(idAuditeur != null) : "L'identifiant de l'auditeur remettant un devoir ne peut pas valoir null.";
      assert(idUV != null) : "L'identifiant de l'UE du devoir à remettre ne peut pas valoir null.";
      assert(idSujet != null) : "L'identifiant du sujet d'examen pour le devoir à remettre ne peut pas valoir null.";
      m_idAuditeur = idAuditeur;
      m_sujetExamen = getSujetExamen(idUV, idSujet);
      log.debug("Demande de correction du casier ({1},{2},{3}) associé au devoirCorrigé {0}.", this, m_idAuditeur, m_sujetExamen.getUV().getId(), m_sujetExamen.getId());
      return(destination(ACCUEIL_CNAM));
}Just before clicking on this button, I check the HTML source code produced by my browser.
And I am still happy.
<input type="hidden" name="j_idt12:remettreDevoir_X1_TP03:j_idt53" value="I023895" />
<input type="hidden" name="j_idt12:remettreDevoir_X1_TP03:j_idt54" value="X1" />
<input type="hidden" name="j_idt12:remettreDevoir_X1_TP03:j_idt55" value="TP03" />
<input type="submit" name="j_idt12:remettreDevoir_X1_TP03:j_idt56" value="Envoyer" onmousedown="if (this.className != 'BtnVertPresse') this.className='BtnVertPresse';" onmouseout="if (this.className != 'BtnVertNonPresse') this.className='BtnVertNonPresse';" onmouseup="if (this.className != 'BtnVertNonPresse') this.className='BtnVertNonPresse';" class="BtnVertNonPresse" />
           </p><input type="hidden" name="javax.faces.ViewState" id="javax.faces.ViewState" value="642372395068906580:4775162548067970543" autocomplete="off" />I then click on it.
Failure:
First, this debug log message:
DevoirRemisBean tag.uv.DevoirRemisBean@9373f7 créé.
Then,
java.lang.AssertionError: L'identifiant de l'auditeur devrait être connu à l'issue de la préparation de la remise de devoir, bean: tag.uv.DevoirRemisBean@9373f7.
     at tag.uv.DevoirRemisBean.check(DevoirRemisBean.java:184)
     at tag.uv.DevoirRemisBean.getSujetExamen(DevoirRemisBean.java:127)
     at sun.reflect.GeneratedMethodAccessor89.invoke(Unknown Source)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java:597)
     at javax.el.BeanELResolver.getValue(BeanELResolver.java:302)Submitting my page, I was expecting
#{correction.doCorrection(idAuditeur, idUV, idSujet)}
to be called. From the DevoirCorrigéBean class.
But instead, another instance of DevoirRemisBean is created, empty... for what internal goal?
And my DevoirCorrigéBean:doCorrection(...) method is not even called.
What can explain what is happening?
Regards,
Grunt.

Answer 1

I removed all my assertions to see how far the submission could go when going unsane.
I discovered that JSF attempts to redisplay my web page, and not to follow on the next one...
... so I have one explanation.
Except that:
There is no fields in the form that require a validation.
(three hidden text fields, and a <h;inputTextarea> but that is not checked or mandatory).
The form is not supposed to fail,
and even if it had too, why the validation step doesn't carry the current managed bean at redisplay time, but instead re-create an empty managed bean?
My form starts with a:
<h:form id="${someId}"> where ${someId} is a scoped variable.
Can it causes a problem during submission? Shall I use only a constant id for my form?
What can you suggest me to do?
Do I have a way to discover what JSF is about to complain against, before it tries to redisplay the page? I see nothing in my logs, but may be I shall redefine a log level somewhere, add one handler or something else?
Regards,
Grunt.