[J2EE] Errore "failed to lazily initialize a collection of role..."

**Mandels85** · 28-11-2010, 16:32

Ciao a tutti,
ho un problema con il mio progetto in J2EE, allora vi riporto i 2 EntityBean di interesse

ENTITY TRAINER

codice:

package com.lesson.entities;

//Import
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

//Relational imports
import javax.persistence.OneToMany;

//Other imports
import java.util.List;

@SuppressWarnings("serial")
@Entity	
@Table(name="trainer")
public class Trainer implements Serializable
{
	//Variables
	private int trainerID;
	private String name;
	private String surname;
	private String email;
	private String password;
	private List<Course> taughtCourseList;
	private List<Notification> unreadNotificationList;
	
	//Getters and Setters
	@Id
	public int getTrainerID()
	{
		return trainerID;
	}
  ........ 
  ........

ENTITY COURSE

codice:

package com.lesson.entities;

//Import
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

//Relational imports
import javax.persistence.ManyToOne;
//import javax.persistence.ManyToMany;
import javax.persistence.OneToMany;

//Other imports
import java.util.List;

@SuppressWarnings("serial")
@Entity	
@Table(name="course")
public class Course implements Serializable
{
	//Variables
	private int courseID;
	private String title;
	private String field;
	private Trainer trainer;
	private List<Student> registeredStudentList;
	private List<Material> courseMaterialList;
	private List<Test> courseTestList;
	
	//Getters and Setters
	@Id
	public int getCourseID()
	{
		return courseID;
	}
.......
.......

Allora quando il client vuole creare un nuove Professore, utilizza il seguente metodo:

codice:

package com.lesson.controllers;


import java.util.ArrayList;
import java.util.Hashtable;
import java.util.List;

import com.lesson.entities.*;

import javax.ejb.EJB;
import javax.ejb.Stateless;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.NonUniqueResultException;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import org.jboss.ejb3.annotation.RemoteBinding;

@Stateless 
@RemoteBinding(jndiBinding="TrainerManagerRemote") 
public class TrainerManagerBean implements TrainerManagerRemote 
{

	@PersistenceContext(unitName="lesson")
	private EntityManager manager;
	@EJB
	private CourseManagerLocal cml;
	
	public boolean createTrainer(TrainerRequest ntr) throws Exception
	{
		if (ntr.getEmail() == null || ntr.getName() == null || ntr.getPassword() == null ||
				ntr.getSurname() == null || ntr.getTrainerID() <= 0) 
			throw new IllegalArgumentException("Invalid null fields in patientRequest"); 
		
		//Check if trainer is already into DB
		Query q = manager.createQuery("select t from Trainer as t where t.trainerID = ?1");
		q.setParameter(1, ntr.getTrainerID());
		Trainer t = null;
		try
		{
			t = (Trainer)q.getSingleResult();
			if (t != null ) throw new NonUniqueResultException("Trainer "+ ntr.getTrainerID() +"already present in DB");
		} catch(NoResultException ex) {}
		
		t = new Trainer();
		t.setTrainerID(ntr.getTrainerID());
		t.setName(ntr.getName());
		t.setSurname(ntr.getSurname());
		t.setEmail(ntr.getEmail());
		t.setPassword(ntr.getPassword());
		List<Course> courseList = new ArrayList<Course>();
		t.setTaughtCourseList(courseList);
		List<Notification> notificationList = new ArrayList<Notification>();
		t.setUnreadNotificationList(notificationList);
		
		manager.persist(t);		
		return true;
	}

Considerate pure il "TrainerRequest come se fosse un oggetto di tipo Trainer...

Ora viene il problema:
Mettiamo che venga registrato un nuovo corso tenuto dal professore appena creato. Come posso fare per inserire nella List<Course> presente nell'entity Trainer (professore) il nuovo corso da lui insegnato?

Inizialmente ho pensato di modificare quella lista all'atto della creazione di un nuovo corso, quindi dal SessionBean di Course tramite:

codice:

public void setCourse(CourseRequest courseRequest) throws Exception
	{
		Course c = new Course();
		c.setCourseID(courseRequest.getCourseID());
		c.setCourseMaterialList(null);
		c.setCourseTestList(null);
		c.setField(courseRequest.getField());
		c.setRegisteredStudentList(null);
		c.setTitle(courseRequest.getTitle());
		
		// Retrieve PatientManager
		TrainerManagerRemote tmr;
		try
		{
			InitialContext ctx = new InitialContext();
			tmr = (TrainerManagerRemote) ctx.lookup("TrainerManagerRemote");	
		}
		catch(Exception ne)
		{
			ne.printStackTrace();
			throw new Exception("Cannot instantiate Trainer Manager", ne);
		}
		
		Trainer trainer = tmr.getTrainerData(courseRequest.getTrainerID());
		if(trainer == null) throw new Exception("Trainier with id=" + courseRequest.getTrainerID() + " does not exist");
		c.setTrainer(trainer);
		manager.persist(c);
		List<Course> temp = new ArrayList<Course>();
		temp.add(c);
		trainer.setTaughtCourseList(temp);
		tmr.updateTrainer(trainer);
	}

L'esecuzione non sembra generare eccezioni...tuttavia quando dal client cerco di accedere alla lista sopra citata ottengo...

codice:

IWAV0055I Java Bean lesson.client.Main started with the main method
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.lesson.entities.Trainer.taughtCourseList, no session or session was closed
	at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:380)
	at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:372)
	at org.hibernate.collection.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:119)
	at org.hibernate.collection.PersistentBag.size(PersistentBag.java:248)
	at lesson.client.Main.getTrainer(Main.java:116)
	at lesson.client.Main.main(Main.java:31)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.eclipse.ve.internal.java.vce.launcher.remotevm.JavaBeansLauncher.main(JavaBeansLauncher.java:79)

Il Client è il seguente, il metodo che uso per leggere i dati di un Trainer è getTrainerData(...), il quale generà però l'errore sopra riportato.

codice:

package lesson.client;

import java.util.ArrayList;
import java.util.Hashtable;
import java.util.List;

import javax.naming.Context;
import javax.naming.InitialContext;
import com.lesson.controllers.*;
import com.lesson.entities.*;

public class Main 
{

	static TrainerManagerRemote pm;
	
	public static void main(String[] args) 
	{
		try 
		{
			Context jndiContext = null;

			jndiContext = getInitialContext();
			Object ref = jndiContext.lookup("TrainerManagerRemote");
			pm = (TrainerManagerRemote)ref;
			
			//logIn();
			//createTrainer();
			//createCourse();
			//updateTrainer();
			getTrainer();
			
			
		} catch (Exception e) { e.printStackTrace();}

	}
	
	public static void logIn()
	{
		try 
		{
			if(pm.logIn(11111, "111111"))
			System.out.println("[DEBUG]--Logged");
			else
				System.out.println("[DEBUG]--Not Logged");
	
		} catch (Exception e) {}

	}
	
	public static void updateTrainer()
	{
		Trainer t = new Trainer();
		t.setEmail("cristianmandelli@gmai.com");
		t.setName("Cristian");
		t.setSurname("Mandelli");
		t.setPassword("02041985");
		t.setTrainerID(1111);
		t.setUnreadNotificationList(null);
		List<Course> list = new ArrayList<Course>();
		list.add(pm.getCourseData(1234));
		t.setTaughtCourseList(list);
		
		try 
		{
			pm.updateTrainer(t);
		
		} catch (Exception e) 
			{
				e.printStackTrace();
			}
	}
	
	public static void createTrainer()
	{
		TrainerRequest t = new TrainerRequest(2222, "Deborah", "Zamponi", "deborah.zamponi@gmail.com", "110585");
		try 
		{
			if(pm.createTrainer(t))
			System.out.println("[DEBUG]--Trainer created");
							
		} catch (Exception ex) 
			{
				ex.printStackTrace();
			}
	}
	
	public static void createCourse()
	{
		
		CourseRequest c = new CourseRequest(1234, "SoftwareEngeneering 1", "Computer Science", 2222);
		try 
		{
			if(pm.createCourse(c));
			System.out.println("[DEBUG]--Course created");
			
		} catch (Exception ex) 
			{
				ex.printStackTrace();
			}
	}
	
	public static void getTrainer()
	{
		Trainer t = null;
		try
		{
			t = pm.getTrainerData(2222);
		} catch (Exception ex)
			{
				ex.printStackTrace();
			}
		
		if(t != null)
		{
			System.out.println("Courses List:" + t.getTaughtCourseList().size());
		}
		
	}
	
	static public Context getInitialContext() throws Exception
	{
		Hashtable<String,String> env = new Hashtable<String,String>();
		env.put(Context.INITIAL_CONTEXT_FACTORY,"org.jnp.interfaces.NamingContextFactory");
		env.put(Context.PROVIDER_URL,"localhost:1099");

		return new InitialContext(env);
	}

}

qualche suggerimento circa dove sia il mio errore??

Cristian

Discussione: [J2EE] Errore "failed to lazily initialize a collection of role..."

Strumenti discussione

Ricerca discussione

Visualizza

Visualizzazione discussione

[RISOLTO] - J2EE - errore (failed to lazily initialize a collection of role...)

Permessi di invio