java.lang.NullPointerException selectOneMenu convertor - jsf

Question

I have a class Specialization
public class Specialization implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#Basic(optional = false)
#NotNull
#Column(name = "id")
private Integer id;
#Basic(optional = false)
#NotNull
#Size(min = 1, max = 45)
#Column(name = "name")
private String name;
#OneToMany(cascade = CascadeType.ALL, mappedBy = "specialization")
private Collection<Doctor> doctorCollection;
In my webpage i have a selectOneMenu
<h:selectOneMenu value="#{specializationMB.specialization}"
converter="#{specializationConverter}">
<f:selectItems value="#{specializationMB.allSpecializations}" var="specialization"
itemLabel="#{specialization.name}" itemValue="#{specialization}" />
</h:selectOneMenu>
GenericDao where is the find method
public abstract class GenericDao<T> {
#PersistenceContext
private EntityManager em;
private Class<T> entityClass;
public GenericDao(Class<T> entityClass) {
this.entityClass = entityClass;
}
public void create(T entity) {
em.persist(entity);
}
public void delete(T entity) {
T toRemoved = em.merge(entity);
em.remove(toRemoved);
}
public T update(T entity) {
return em.merge(entity);
}
public T find(int entityID) {
return em.find(entityClass, entityID);
}
#SuppressWarnings({"unchecked", "rawtypes"})
public List<T> findAll() {
CriteriaQuery cq = em.getCriteriaBuilder().createQuery();
cq.select(cq.from(entityClass));
return em.createQuery(cq).getResultList();
}
}
I create the converter for my class Specialization
public class SpecializationConverter implements Converter{
private static SpecializationDao sdao = new SpecializationDao();
#Override
public Object getAsObject(FacesContext context, UIComponent component, String value) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
return sdao.find(new Integer(value));
}
#Override
public String getAsString(FacesContext context, UIComponent component, Object value) {
//throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
return ((Specialization) value).getId().toString();
}
}
But I get an error with my selectOneMenu, when i go to the next page.
java.lang.NullPointerException
at pl.ePrzychodnia.dao.GenericDao.find(GenericDao.java:40)
at pl.ePrzychodnia.converter.SpecializationConverter.getAsObject(SpecializationConverter.java:24)
at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:171)
at com.sun.faces.renderkit.html_basic.MenuRenderer.convertSelectOneValue(MenuRenderer.java:202)
at com.sun.faces.renderkit.html_basic.MenuRenderer.getConvertedValue(MenuRenderer.java:319)
at javax.faces.component.UIInput.getConvertedValue(UIInput.java:1030)
at javax.faces.component.UIInput.validate(UIInput.java:960)
at javax.faces.component.UIInput.executeValidate(UIInput.java:1233)
at javax.faces.component.UIInput.processValidators(UIInput.java:698)
at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
at javax.faces.component.UIForm.processValidators(UIForm.java:253)
at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1172)
at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:76)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:722)
I don't now why. Can anyone help?

Answer 1

private static SpecializationDao sdao = new SpecializationDao();
Assuming this DAO is a subclass of your GenericDAO, can you tell me when is the EntityManager injected? Let the container create your DAO! Your EntityManager is not injected, therefore you get the NPE.
I would create a stateless session bean (if you work with EJB) and then inject it into the converter.
#Stateless
public class SpecializationService extends GenericCRUDService {...}
public class SpecializationConverter implements Converter{
#Inject
private SpecializationService specializationService;
...
I also think that the term and pattern DAO is a bit outdated. Read about it for example here.