Reason for stack overflow exception while trying to read hibernate managed objects

Hello All,

I'm writing some sample codes in hibernate to understand the association and just started with One-One mapping. I ran into an issue where it says

Hibernate: select student0_.STUDENT_ID as STUDENT1_1_0_, student0_.STUDENT_NAME as STUDENT2_1_0_, 
    student0_.STUDENT_ADDRESS as STUDENT3_1_0_ from STUDENT student0_ where student0_.STUDENT_ID=?
Exception in thread "main" java.lang.StackOverflowError
	at javassist.util.proxy.RuntimeSupport.find2Methods(RuntimeSupport.java:53)
	at com.hibertut.beans.Student_$$_javassist_1.toString(Student_$$_javassist_1.java)
	at java.lang.String.valueOf(String.java:2826)
	at java.lang.StringBuilder.append(StringBuilder.java:115)
	at com.hibertut.beans.Address.toString(Address.java:73)
	at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:197)
	at com.hibertut.beans.Address_$$_javassist_0.toString(Address_$$_javassist_0.java)
	at java.lang.String.valueOf(String.java:2826)
	at java.lang.StringBuilder.append(StringBuilder.java:115)
	at com.hibertut.beans.Student.toString(Student.java:40)
	at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

Below are my codes

Address.java

Student.java

Address.hbm.xml

Student.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
                                   "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.hibertut.beans">
	<class name="Student" table="STUDENT">
		<id name="studentId" type="java.lang.Long">
			<column name="STUDENT_ID"/>
				<generator class="assigned"/>
		</id>
                 
  
[b]  	<many-to-one name="studentAddress" class="Address" not-null="true" cascade="all" unique="true">
  		<column name="STUDENT_ADDRESS"></column>
  	</many-to-one>[/b]
</class>
</hibernate-mapping>

Now my client program is as below
[code]    
package com.hibertut.clients;

import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.HibernateException;
import org.hibernate.SessionFactory;
import com.hibertut.utils.*;
import com.hibertut.beans.*;

import java.util.*;
import java.io.*;
import java.sql.Date;

public class HiberTut {
	private SessionFactory sessionFactory=null;
	private Session session=null;
	public HiberTut(){
		sessionFactory=FactoryLocator.getInstance();
	}
	
	public SessionFactory getFactory(){
		return sessionFactory;
	}
	
	public void setSession(Session session){
		this.session=session;
	}
	
	public void setSession(){
		this.session=sessionFactory.openSession();
	}
	
	public Session getSession(){
		return sessionFactory.openSession();
	}
	
	public Object create(Session session,Object obj,String objType){
		Transaction trans=session.beginTransaction();
		Object ret=null;;
		trans.begin();
		if (objType.equalsIgnoreCase("Event")){
			ret=session.save((Event)obj);
		}
		else if (objType.equalsIgnoreCase("Location")){
			ret=session.save((Location)obj);
		}
		else if (objType.equalsIgnoreCase("Student")){
			ret=session.save((Student)obj);
		}
		else if (objType.equalsIgnoreCase("Address")){
			ret=session.save((Address)obj);
		}
		trans.commit();
		session.flush();
		return ret;
	}
	
	public void update(Session session,Object obj,String objType){
	//ToDo nothing
	}
	
	public Object retrieve(Session session,long id,String objType){
		Object object=null;
		if (objType.equalsIgnoreCase("Event"))
			object=(Event)session.load(Event.class,id);
		else if (objType.equalsIgnoreCase("Location"))
			object=(Location)session.load(Location.class,id);
		else if (objType.equalsIgnoreCase("Address"))
			object=(Address)session.load(Address.class,id);
		else if (objType.equalsIgnoreCase("Student"))
			object=(Student)session.load(Student.class,id);
		
		return object;
	}

public static void main(String[] args)throws Exception{
		HiberTut hiber=new HiberTut();
		Session session=null;
		int location_Id=0;
		int event_Id=0;
		Integer id=null;
		String bool=null;
		
                               /*Address address1 = new Address(1,"123 Main St","Apt D","St Louis","MO",61704); 
		            
		Address address2 = new Address(2,"321 Main St","Apt D","St Louis","MO",61704); 
		 
		Student student1 = new Student(1,"XYZ",address1); 
		            
		Student student2 = new Student(2,"ABC",address1); 
		
		address1.setStudent(student1);
		address2.setStudent(student2);
	              */	
		session=hiber.getSession();
		//hiber.create(session,address1,"Address");
		//hiber.create(session,address2,"Address");
	
		for(int i=1;i<=2;i++){
			Address adr=(Address)hiber.retrieve(session, i, "Address");
			System.out.println("Address 1"+ adr.getAddress1());
			System.out.println("Address 2"+ adr.getAddress2());
			System.out.println("City"+ adr.getCity());
			System.out.println("State"+ adr.getState());
			System.out.println("Zipcode"+ adr.getZipCode());
			[b]//System.out.println("Student Name"+adr.getStudent());
			//System.out.println("Address is "+adr);[/b]	     //These two statements cause the StackOverFlowError	
                                }
		System.out.println("Completed");
	}
}

The reason which I'm thinking of here is when we say getStudent(), toString() method of Student class invoked as expected and in toString(), we have a reference of Address and it would invoke toString() method defined in Address class. This is getting into the infamous vicious circle of circular reference and finally throwing the error. I'm almost certain on this, as when I print only student name, it is working fine. But it is throwing error, when I try to refer Address from Student object.

My questions
1) Is my understanding of the error correct ? Or is there something else that could have caused the issue (which I'm certainly not hoping for).
2) Are there any hidden caveats in this code, which I should be aware of ?
3) How can this be better designed ?

I'm not sure I understand why you're doing this--can't you just save an object without casting it? The save method, after all, doesn't have specific save methods for each class.

But yes, you're in an infinite loop.

And please don't try to include BB Code markup in source code--surely you can see it didn't have the intended effect.

Yes, I can certainly persist the objects without explicit casting. That was an overlook from my side.

But some how I'm thinking that this bidirectional association is not correctly designed and there is a high risk of circular dependencies and references. Is there any good approach/industry standard that can be suggested espicially while handling bidirectional assocation.