JPA: Best practice to get and close EntityManagerFactory to avoid Unknown entity bean class error !

Problem Description

After redeploying a WebApplication using JPA you see the following error:

13:02:18.090 Unknown entity bean class: class com.hhu.wfjpa2el.Emp2, 
 please verify that this class has been marked with the @Entity annotation.

13:02:18.091 java.lang.IllegalArgumentException: Unknown entity bean class: class com.hhu.wfjpa2el.Emp2, 
  please verify that this class has been marked with the @Entity annotation.

Solution

• Restart your WEBServer   or
  
• Install a ServletContextListener and close the EMF during contextDestroyed() Event

JAVA Code for implementing a WebListener

package com.hhu.wfjpa2el;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import org.slf4j.LoggerFactory;

@WebListener
public class EMF implements ServletContextListener {

    private static EntityManagerFactory emf;
    final private static String pu = "jpaELPU";
    final static org.slf4j.Logger logger = LoggerFactory.getLogger(ServletContextListenerImpl.class);
    
    @Override
    public void contextInitialized(ServletContextEvent event) {
        logger.info("+++ ServletContextListener : contextInitialized - Inititalizing EMF for PU: " + pu);
        emf = Persistence.createEntityManagerFactory(pu);
        logger.info("+++ ServletContextListener : contextInitialized - Init EMF done for PU: " + pu);
    }

    @Override
    public void contextDestroyed(ServletContextEvent event) {
        logger.info("+++ ServletContextListener : contextDestroyed - Closing EMF for PU: " + pu);
        emf.close();
        logger.info("+++ ServletContextListener : contextDestroyed - Closed EMF done for PU " + pu);
    }

    public static EntityManager createEntityManager() {
        if (emf == null) {
            throw new IllegalStateException("Context is not initialized yet.");
        }
        return emf.createEntityManager();
    }
}

Initialize your Entity Manager by running :  em = EMF.createEntityManager();
Java Code: 
public static EntityManager getEntityManager() 
      {
        EntityManager em = threadLocal.get();
        if (em == null) 
          {
          // setRunTimeInfo(getRunTimeInfo() + Tools.add_hmtl_pre_tag("Creating Entity Manager ! "  ));
            if ( enableLogger )            
                logger.info("Creating Entity Manager Factory ..." );
            em = EMF.createEntityManager();
            threadLocal.set(em);
          }
        return em;
      }

Testing the Code wiht maven deploy/undeploy command

Deploy the WebApplication 
[oracle@wls1 WFJPA2EL]$  mvn wildfly:deploy

Wilfdly Log report:  
13:11:23,170 INFO  [stdout] (MSC service thread 1-4) 13:11:23 [MSC service thread 1-4] INFO  c.h.w.ServletContextListenerImpl - i
                   +++ ServletContextListener : contextInitialized - Init EMF done for PU: jpaELPU
13:11:23,173 INFO  [javax.enterprise.resource.webcontainer.jsf.config] (MSC service thread 1-4) Initializing Mojarra 2.2.8-jbossorg-1 20140822-1131 for context '/WFJPA2EL-1.0'
13:11:23,518 INFO  [org.wildfly.extension.undertow] (MSC service thread 1-4) JBAS017534: Registered web context: /WFJPA2EL-1.0
13:11:24,010 INFO  [org.jboss.as.server] (management-handler-thread - 1) JBAS018559: Deployed "WFJPA2EL-1.0.war" (runtime-name : "WFJPA2EL-1.0.war")

Undeploy the WebApplication 
[oracle@wls1 WFJPA2EL]$   mvn wildfly:undeploy 

Wilfdly Log report:  
13:11:23,170 INFO  [stdout] (MSC service thread 1-4) 13:11:23 [MSC service thread 1-4] INFO  c.h.w.ServletContextListenerImpl - i
                    +++ ServletContextListener : contextInitialized - Init EMF done for PU: jpaELPU
13:11:23,173 INFO  [javax.enterprise.resource.webcontainer.jsf.config] (MSC service thread 1-4) Initializing Mojarra 2.2.8-jbossorg-1 20140822-1131 for context '/WFJPA2EL-1.0'
13:11:23,518 INFO  [org.wildfly.extension.undertow] (MSC service thread 1-4) JBAS017534: Registered web context: /WFJPA2EL-1.0
13:11:24,010 INFO  [org.jboss.as.server] (management-handler-thread - 1) JBAS018559: Deployed "WFJPA2EL-1.0.war" (runtime-name : "WFJPA2EL-1.0.war")
13:13:02,751 INFO  [org.wildfly.extension.undertow] (MSC service thread 1-7) JBAS017535: Unregistered web context: /WFJPA2EL-1.0

Reference

• Best practice to get EntityManagerFactory