NullPointerException in creating Session Object using Hibernate

[Agraj Mangal]

Hi,

I'm new to hibernate and was trying my first app with hibernate reading this tutorial: http://www.tutcity.com/view/first-hibernate.6357.html

My hibernate.cfg.xml file looks like

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
	<session-factory>
		<property name="connection.url">
			jdbc:mysql://localhost/firsthibernate
		</property>
		<property name="connection.username">root</property>
		<property name="connection.driver_class">
			com.mysql.jdbc.Driver
		</property>
		<property name="dialect">
			org.hibernate.dialect.MySQLDialect
		</property>
		<property name="connection.password">mysql</property>
		<property name="transaction.factory_class">
			org.hibernate.transaction.JDBCTransactionFactory
		</property>
		<!-- thread is the short name for
			org.hibernate.context.ThreadLocalSessionContext
			and let Hibernate bind the session automatically to the thread
		-->
		<property name="current_session_context_class">thread</property>
		<!-- this will show us all sql statements -->
		<property name="hibernate.show_sql">true</property>
		<!-- mapping files -->
		<mapping resource="com/Honey.hbm.xml" />
	</session-factory>
</hibernate-configuration>

-----------------------------------------------------------------------------------------------------------

My honey.hbm.xml looks like

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD
3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>
	<class name="com.Honey" table="honey">
		<id name="id" column="id">
			<generator class="increment" />
		</id>
		<property name="name" column="fooname" />
		<property name="taste" column="bartaste" />
	</class>
</hibernate-mapping>

-----------------------------------------------------------------------------------------------------

My Honey.java looks like

package com;

public class Honey {
	
	private Integer id;
	private String name;
	private String taste;
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getTaste() {
		return taste;
	}
	public void setTaste(String taste) {
		this.taste = taste;
	}	
	
	public Honey(){
		
	}
	
	public String toString(){
		return "Honey: "+getId()+" Name: "+getName()+" Taste: "+getTaste();
	}

}

--------------------------------------------------------------------------------------------------

My SessionFactoryUtil.java looks like

package com;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

public class SessionFactoryUtil {
	
	private static SessionFactory sessionFactory;
	
	private SessionFactoryUtil(){	
	}
	
	static{
		Configuration config = new Configuration();
		config.addFile("E:/Eclipse/workspace/FirstHibernateExample/src/hibernate.cfg.xml");
		sessionFactory = config.configure().buildSessionFactory();

		//sessionFactory = new Configuration().configure().buildSessionFactory();
	}
	
	public static SessionFactory getInstance(){
		return sessionFactory;
	}

	public Session openSession(){
		return sessionFactory.openSession();
	}
	
	public Session getCurrentSession(){
		return sessionFactory.getCurrentSession();
	}
	
	public static void close(){
		if(sessionFactory!=null)
			sessionFactory.close();
		sessionFactory = null;
	}
	
}

--------------------------------------------------------------------------------------------------

Finally my stand alone java program, the client that tests this application "TestExample.java" looks like

package com;

import java.util.Iterator;
import java.util.List;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class TestExample {
	
	final static Logger logger = LoggerFactory.getLogger(TestExample.class);

	public static void main(String[] args){
		Honey forestHoney = new Honey();
		forestHoney.setName("Forest Honey");
		forestHoney.setTaste("Very Tasty");
		createHoney(forestHoney);
		
		Honey countryHoney = new Honey();
		countryHoney.setName("county honey");
		countryHoney.setTaste("Not Bad");
		createHoney(countryHoney);
		
		// our instance have a primary key row now
		
		logger.debug("{}",forestHoney);
		logger.debug("{}", countryHoney);
		
		listHoney();
		
		deleteHoney(countryHoney);
		listHoney();
		
		forestHoney.setName("northern forest honey");
		updateHoney(forestHoney);
		listHoney();
	}
	
	private static void updateHoney(Honey honey){
		Transaction tx = null;
		Session session = SessionFactoryUtil.getInstance().getCurrentSession();
		try{
			tx = session.beginTransaction();
			session.update(honey);
			tx.commit();
		}
		catch(RuntimeException e){
			if(tx != null && tx.isActive()){
				try{
					tx.rollback();
				}
				catch(HibernateException e2){
					logger.debug("error in rollbacking in update");
				}
				throw e;
			}
		}
	}
	
	private static void deleteHoney(Honey honey){
		Transaction tx = null;
		Session session = SessionFactoryUtil.getInstance().getCurrentSession();
		try{
			tx = session.beginTransaction();
			session.delete(honey);
			tx.commit();
		}
		catch(RuntimeException e){
			if(tx!=null && tx.isActive()){
				try{
					tx.rollback();
				}
				catch(HibernateException e2){
					logger.debug("Error in roll back in delete");
				}
				throw e;
			}
		}
	}
	
	private static void listHoney(){
		Transaction tx = null;
		Session session = SessionFactoryUtil.getInstance().getCurrentSession();
		try{
			tx = session.beginTransaction();
			List honeys = session.createQuery("select h from Honey as h").list();
			
			for(Iterator iter=honeys.iterator(); iter.hasNext();){
				Honey element = (Honey) iter.next();
				logger.debug("{}", element);
			}
			tx.commit();
		}
		catch(RuntimeException e){
			if(tx!=null && tx.isActive()){
				try{
					tx.rollback();
				}
				catch(HibernateException e1){
					logger.debug("Error in rollback");
				}
			}
			throw e;
		}
	}
	
	private static void createHoney(Honey honey){
		Transaction tx = null;
		Session session = SessionFactoryUtil.getInstance().getCurrentSession();
		try{
			tx = session.beginTransaction();
			if(session==null){
				logger.debug("session is null");
				System.out.println(session==null);
			}
			session.save(honey);
			tx.commit();
			
		}
		catch(RuntimeException e){
			if(tx!=null && tx.isActive()){
				try{
				// second try-catch block as the rollback could fail as well
					tx.rollback();
				}
				catch(HibernateException e1){
					logger.debug("Error rolling back transaction");
				}
			}
			// throw the first exception
			throw e;
		}
	}
}

---------------------------------------------------------------------------------------------------------

The exception stack trace looks like

Exception in thread "main" java.lang.NullPointerException
at com.mysql.jdbc.PreparedStatement.asSql(PreparedStatement.java:578)
at com.mysql.jdbc.PreparedStatement.asSql(PreparedStatement.java:516)
at com.mysql.jdbc.PreparedStatement.toString(PreparedStatement.java:3758)
at java.lang.String.valueOf(Unknown Source)
at java.lang.StringBuffer.append(Unknown Source)
at com.mysql.jdbc.trace.Tracer.printParameters(Tracer.aj:240)
at com.mysql.jdbc.trace.Tracer.printEntering(Tracer.aj:167)
at com.mysql.jdbc.trace.Tracer.entry(Tracer.aj:126)
at com.mysql.jdbc.trace.Tracer.ajc$before$com_mysql_jdbc_trace_Tracer$1$f51c62b8(Tracer.aj:45)
at com.mysql.jdbc.Connection.registerStatement(Connection.java)
at com.mysql.jdbc.Statement.<init>(Statement.java:267)
at com.mysql.jdbc.PreparedStatement.<init>(PreparedStatement.java:435)
at com.mysql.jdbc.ServerPreparedStatement.asSql(ServerPreparedStatement.java:360)
at com.mysql.jdbc.PreparedStatement.asSql(PreparedStatement.java:516)
at com.mysql.jdbc.ServerPreparedStatement.toString(ServerPreparedStatement.java:2433)
at java.lang.String.valueOf(Unknown Source)
at java.lang.StringBuffer.append(Unknown Source)
at com.mysql.jdbc.trace.Tracer.printParameters(Tracer.aj:240)
at com.mysql.jdbc.trace.Tracer.printEntering(Tracer.aj:167)
at com.mysql.jdbc.trace.Tracer.entry(Tracer.aj:126)
at com.mysql.jdbc.trace.Tracer.ajc$before$com_mysql_jdbc_trace_Tracer$1$f51c62b8(Tracer.aj:45)
at com.mysql.jdbc.Connection.registerStatement(Connection.java)
at com.mysql.jdbc.Statement.<init>(Statement.java:267)
at com.mysql.jdbc.PreparedStatement.<init>(PreparedStatement.java:417)
at com.mysql.jdbc.ServerPreparedStatement.<init>(ServerPreparedStatement.java:290)
at com.mysql.jdbc.Connection.prepareStatement(Connection.java:4656)
at com.mysql.jdbc.Connection.prepareStatement(Connection.java:4573)
at org.hibernate.jdbc.AbstractBatcher.getPreparedStatement(AbstractBatcher.java:534)
at org.hibernate.jdbc.AbstractBatcher.prepareSelectStatement(AbstractBatcher.java:145)
at org.hibernate.id.IncrementGenerator.getNext(IncrementGenerator.java:107)
at org.hibernate.id.IncrementGenerator.generate(IncrementGenerator.java:68)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:122)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:562)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:550)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:546)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:342)
at $Proxy0.save(Unknown Source)
at com.TestExample.createHoney(TestExample.java:118)
at com.TestExample.main(TestExample.java:19)

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I'm sorry to have written all my code since i do not know because of which settings the error is coming.
I read a similar problem post on this forum : http://www.coderanch.com/t/216619/Object-Relational-Mapping/java/HI-got-null-pointer-exception
but the solution mentioned there did not helped me.

Is there a problem in hibernate.cfg.xml file ?
Why is my session null ??
because as far as i can understand it is throwing NullPointerException when i try and call any function on session object
like it is giving error in
session.save(honey)
in
createHoney(honey) method

Please help and reply what could be the problem

Best Regards,
Agraj