Failed to lazily initialize a collection of role

What is org.hibernate.LazyInitializationException ?


I have faced this issue during my project development when I was trying to fix few testing issue. As per the scenario a one-to-many relation from VoiceServiceFileUpload class to VoiceServiceRequest class. When I want to load the VoiceServiceRequests that belongs to a voiceServiceFileUpload , I got this error. 

It seems that the error is caused by Hibernate lazily loading the VoiceServiceRequest  collection i.e. it returns a list of VoiceServiceRequest Id's only to the view. When the view tries to display the data, the session has been closed and hence, the error. Because , by default the FetchType is lazy true. After subsequent investigation and debug , I fix this by using below possible ways.


Error Log :-

ERROR, a7e3d058-4b9a-494a-87a4-08718d397b09: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: au.com.biz.service.sdp.bizservice.vmprovision.scheduler.domain.model.VoiceServiceFileUpload.VoiceServiceRequests, no session or session was closed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: au.com.biz.service.sdp.bizservice.vmprovision.scheduler.domain.model.VoiceServiceFileUpload.VoiceServiceRequests, no session or session was closed
        at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:358)
        at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:350)
        at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:343)
        at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:86)
        at org.hibernate.collection.PersistentSet.hashCode(PersistentSet.java:411)
        at java.util.HashMap.getEntry(HashMap.java:424)
        at java.util.HashMap.containsKey(HashMap.java:415)
        at java.util.HashSet.contains(HashSet.java:184)
        at org.apache.commons.lang.builder.ToStringStyle.isRegistered(ToStringStyle.java:137)
        at org.apache.commons.lang.builder.ToStringStyle.appendInternal(ToStringStyle.java:421)
        at org.apache.commons.lang.builder.ToStringStyle.append(ToStringStyle.java:395)
        at org.apache.commons.lang.builder.ToStringBuilder.append(ToStringBuilder.java:840)
        at au.com.biz.service.sdp.bizservice.vmprovision.scheduler.domain.model.VoiceServiceFileUpload.toString(VoiceServiceFileUpload.java:68)
        at java.lang.String.valueOf(String.java:2826)
        at java.lang.StringBuffer.append(StringBuffer.java:219)
        at org.apache.commons.lang.builder.ToStringStyle.appendDetail(ToStringStyle.java:545)
        at org.apache.commons.lang.builder.ToStringStyle.appendInternal(ToStringStyle.java:509)
        at org.apache.commons.lang.builder.ToStringStyle.append(ToStringStyle.java:395)
        at org.apache.commons.lang.builder.ToStringBuilder.append(ToStringBuilder.java:840)
        at au.com.biz.service.sdp.bizservice.vmprovision.scheduler.domain.model.VoiceServiceRequest.toString(VoiceServiceRequest.java:106)
        at au.com.biz.service.sdp.bizservice.vmprovision.scheduler.domain.dao.hibernate.HibernateVoiceServiceRequestDao.update(HibernateVoiceServiceRequestDao.java:113)
        at au.com.biz.service.sdp.bizservice.vmprovision.scheduler.facade.spring.SpringVoiceServiceBatchJobFacade.updateRequestProvisionSendDate(SpringVoiceServiceBatchJobFacade.java:180)
        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.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:310)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
        at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
        at com.sun.proxy.$Proxy548.updateRequestProvisionSendDate(Unknown Source)
        at au.com.biz.service.sdp.infraservice.scheduler.application.job.VMProvisionBatchJob.executeJob(VMProvisionBatchJob.java:183)
        at au.com.biz.service.core.scheduler.SchedulerJob.executeTrigger(SchedulerJob.java:129)
        at au.com.biz.service.core.scheduler.SchedulerJob.execute(SchedulerJob.java:76)
        at org.quartz.core.JobRunShell.run(JobRunShell.java:203)
        at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:520)


Below the sample configuration for the entity.There is the context configuration , which is missing in this post.The configuration is configured as lazy loading true.
,  

VoiceServiceFileUpload Entity :-

package javadevelopersguide.lab;
import java.util.HashSet;import java.util.Set;
import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.Id;import javax.persistence.OneToMany;import javax.persistence.Table;
@Entity@Table(name="voiceservicefileupload")public class VoiceServiceFileUpload{
@Id @Column(name="FILE_ID") private int FILE_ID; @Column(name="fileName") private String fileName; @OneToMany(cascade = CascadeType.ALL, mappedBy = "voiceServiceFileUpload") private Set<VoiceServiceRequest> VoiceServiceRequests= new HashSet<VoiceServiceRequest>(0); /** * Setter and Getter Method below */}

VoiceServiceRequest Entity :-

package jdevelopersguide.lab;
import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.ManyToOne;import javax.persistence.Table;

@Entity@Table(name="voiceservicerequest")public class VoiceServiceRequest{
@Id @Column private int ID; @Column(name="serivcename") private String serviceName; @ManyToOne(fetch = FetchType.EAGER, optional = true) @JoinColumn(name = "FILE_ID", nullable = true) private VoiceServiceFileUpload voiceServiceFileUpload; /** * Setter and Getter Method below */
}

Option 1 -

You can use OpenEntityManagerInViewFilter to open your session in view mode. So, you need to configure this in your web.xml file. But, I didn't do this :) . Because I had few more limitation as per my project structure and architecture. 

Add the below code snippet into your web.xml

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

<filter><filter-name>OpenEntityManagerInViewFilter</filter-name><filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class></filter><filter-mapping><filter-name>OpenEntityManagerInViewFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping>

Option 2 -

This issue is happening the ,because the session has closed before you load the collection.So, you can open a new session, but its not suggested.So, I didn't do this :)

After gooooogle almost few articles , I found you can also try @Transactional for that method.Because,it makes your session active. But, I didn't try this. But , you can try your luck :)

Option 3 -

Finally , I have configured the VoiceServiceFileUpload to load eager (i.e fetch = FetchType.EAGER) and it resolved my issue.

Working fix :-

@OneToMany(cascade = CascadeType.ALL, mappedBy = "voiceServiceFileUpload",fetch = FetchType.EAGER) private Set<VoiceServiceRequest> VoiceServiceRequests= new HashSet<VoiceServiceRequest>(0);

Hope this will help you and will save your all day :::)

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Many-to-One relationship in hibernate - @ManyToOne Example

As we all know Hibernate is an easy and fast framework for work with any Database using Java language. This example show how to work with Many-To-One relationship in Hibernate.


I have used MySQL as database (Download Here) and Hibernate 3 jar files (Download Here). Also for applying Many-To-One relation we have used annotation. Even you can do this by using .xml config also, but that's too old and no one is using that now-a-days.

Create table department and employee :-

 Table department :

CREATE TABLE `department` (
  `deptid` int(11) NOT NULL,
  `deptname` varchar(100) default NULL,
  PRIMARY KEY  (`deptid`)
) ENGINE=InnoDB DEFAULT CHARSET=big5;

Table employee :

CREATE TABLE `employee` (
  `empid` int(11) NOT NULL,
  `empname` varchar(50) default NULL,
  `deptno` int(11) default NULL,
  PRIMARY KEY  (`empid`),
  KEY `deptno` (`deptno`),
  CONSTRAINT `employee_ibfk_1` FOREIGN KEY (`deptno`) REFERENCES `department` (`deptid`)
) ENGINE=InnoDB DEFAULT CHARSET=big5;

In this above both table , many employee could be from one department and implements Many-to-One relationship.


hibernate.cnf.xml

<?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>
        <!-- Adding mysql dialect -->
        <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
           <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <!-- Here jdeveloperguidedb is the database name -->
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/jdeveloperguidedb</property>
           <property name="hibernate.connection.username">root</property>
           <property name="hibernate.connection.password">root</property>
           <!-- show_sql property will help you to show the generated hibernate query on console -->          
           <property name="show_sql" >true</property> 
           <!-- Mapping entity class to hibernate -->
           <mapping class="com.jdeveloperguide.lab.Employee"></mapping> 
           <mapping class="com.jdeveloperguide.lab.Department"></mapping> 
    </session-factory>
</hibernate-configuration>

In this hibernate.cnf.xml file we have configure the initial setup for db , and it will help us to interact with db using hibernate.

Department.java

package com.jdeveloperguide.lab;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="department")
public class Department {

    @Id
    @Column(name="deptid")
    private int deptid;
   
    private String deptname;
   
    public int getDeptid() {
        return deptid;
    }
    public void setDeptid(int deptid) {
        this.deptid = deptid;
    }
    public String getDeptname() {
        return deptname;
    }
    public void setDeptname(String deptname) {
        this.deptname = deptname;
    }
}

Here Department.java is the entity class which we are going to persist or save into db.We have used few annotation here like @Entity ,@Table , @Id , @Column , etc. This entity class looks like a helper class.

@Entity - This annotation will help you to define entity in RDBMS.

@Table - This annotation will help you to define a database table (entity) by specifying name.

 i.e. @Table(name="department").

@Id - This annotation will help you to define the id column , it means the primary key.

@Column - This annotation will help you to define the column name by specifying the column name. If your column name and java variable name are different the you can specify by name. In this example our database column name and variable name are same so, not required specify the column name. Hibernate will automatically match and take care this. But I have used because for better understanding.




Employee.java

package com.jdeveloperguide.lab;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name="employee")
public class Employee {

@Id   
@Column(name="empid")
private int empid;

@Column(name="empname")
private String empname;

@ManyToOne(cascade=CascadeType.ALL)
@JoinColumn(name="deptno")
private Department dept;

public int getEmpid() {
    return empid;
}

public void setEmpid(int empid) {
    this.empid = empid;
}

public String getEmpname() {
    return empname;
}

public void setEmpname(String empname) {
    this.empname = empname;
}

public Department getDept() {
    return dept;
}

public void setDept(Department dept) {
    this.dept = dept;
}   
}

 Here Employee.java is the entity class which we are going to persist or save into db along with Department.We have used few more new annotations here like @ManyToOne , @JoinColumn, etc.
Here we have mapped many-to-one , means many employee from one department.

@ManyToOne - Mapping many-to-one relation with hibernate.

@JoinColumn - This annotation is used for map the reference foreign key for any entity. This indicates the association with entity/table.

 CreateSessionFactory.java

package com.jdeveloperguide.lab;

import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

public class CreateSessionFactory {
    //Single point of access for SessionFactory
    private static final SessionFactory sessionFactory;
    static {
        try {
            //create sesson factory using the config file
            sessionFactory = new AnnotationConfiguration().configure("hibernate.cnf.xml").buildSessionFactory();
        } catch (Throwable ex) {
            throw new ExceptionInInitializerError(ex);
        }
    }
   
    //Static method for exposing the session
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

This class will help to create the SessionFactory object using .xml config file. This class having static method with we can call from any part of this application for getting SessionFactory object.Because , we will create Session object from SessionFactory. 

MainClass.java

package com.jdeveloperguide.lab;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;


public class MainClass {

    /**
     * @param args
     */
    public static void main(String[] args)throws Exception {
        MainClass mainObject=new MainClass();;
        Employee employee=new Employee();
        Department department=new Department();
        department.setDeptid(7);
        department.setDeptname("Computer Science");
       
        employee.setDept(department);
        employee.setEmpid(8);
        employee.setEmpname("Mr. JDeveloper");
        mainObject.saveEmployee(employee);
    }
   
    public void saveEmployee(Employee employee)throws Exception{
        Transaction transaction=null;
        Session session=null;
       
        try{
        //Create and open session
        session = CreateSessionFactory.getSessionFactory().openSession();
        //Create Transaction for maintain a user session
        transaction=session.beginTransaction();
        //Save the employee
        //Also it will save department ,because we have used cascade=CascadeType.ALL in employee
        session.save(employee);
        transaction.commit();
        }catch(HibernateException hibernateException){
            transaction.rollback();
            System.out.println("Error during save into DB :::"+hibernateException);
        }finally{
            session.close();
        }
    }
}

 This MainClass.java is the starting point of this example. Here we will execute our hibernate Many-to-One example and it will persist the data into DB.

Hibernate Generated SQL :-

Hibernate: select department_.deptid, department_.deptname as deptname1_ from department department_ where department_.deptid=?
Hibernate: insert into department (deptname, deptid) values (?, ?)
Hibernate: insert into employee (empname, deptno, empid) values (?, ?, ?)

When we will execute the MainClass.java class , it will generate these above queries by hibernate and these are auto generated. Its generating and showing because, we have mentioned in .xml config file show_sql is true.


Result in DB :-

Department Table

Employee Table

Hope it will help you.

Experienced Java Interview questions asked by CGI

3+ Year experienced java questions asked by CGI.

       1)  Tell me about your self ?

    Ans : Just describe yourself with cool & confidence.

    
2) What you know about our company?

   Ans : Remember , it’s a very crucial question. You must do one R&D before going to interview. You should know about their product, technical stuffs they are working, market value of the company ane other important stuffs.

3) What is transient variable ?

   Ans : Transient variables are not serializable. It helps to avoid a variable to being serialization.

4) Write the code to initialize the inner class members.

Ans : Code here

public class InnerClassTest {

      class innerTest{

            private int age;

           

            public void display(){

                  System.out.println("Age="+age);

            }

      }

      /**

       * @param args

       */

      public static void main(String[] args) {

            InnerClassTest.innerTest innerObj=new InnerClassTest().new innerTest();

            innerObj.age=20;

            innerObj.display();

      }

}

 5) How to retrieve the elements from the collection write the code ?

Ans : Java provides certain interfaces by using that we can retrieve the elements from collection.Example – Iterator, ListIterator and Enumeration.

Example :- ArrayList data retrival

public class ArrayListRetrive {

      /**

       * @param args

       */

      public static void main(String[] args) {

            ArrayList<String> arList=new ArrayList<String>();

            arList.add("Java");

            arList.add("is");

            arList.add("Powerful!!!");

           

            //Retrive elements from ArrayList using Iterator

            Iterator iTer=arList.iterator();

            while(iTer.hasNext()){

                  System.out.println(iTer.next());

            }

      }

}

6) What is static and instance variables and methods ?

Ans : Static variables are per class but the instance variables are per object. All object share a single copy of static variable. In case of static method , no need of object creation for calling static method. The static method can directly call by using class name. Instance method need object for calling.

7) What is dynamic loading and static loading of java class ?

Ans : Dynamic class loading is by Class.forName() , which loads the class dynamically. Also you can use reflection for dynamic class loading. But, the static class loading is working by using ‘new’ keyword.

8) What type of loading is class.forname() ?

Ans : Its dynamically locate and loads the class.

9) What is Hibenate 3 best benfits ?

Ans : There are many benefits of hibernate. But the most benefits are below :-

1.     It reduces the developer effort to writing queries.

2.     Its easy to use with relational object which maps with java class and database relation.

3.     Query tuning is not required and it implements separates cache which is reason for better performance.

10) I have 100 tables and fields. I want to find one table name and  column names.  Write a quey .

Ans :  I have used mySQL database for this below query.

select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME from information_schema.COLUMNS where TABLE_NAME='EMPLOYEE';

 11) How to define a field name in hibernate using annotation ?

          Ans:- @Column  (Its provided by java persistent  API).

 12) What is Synchronization ?

          Ans:- Synchronization is a solution for concurrency issue. Java provide 'synchronized' keyword for implementing this.

  13) The most commonly used classes in collectionsn ?

Ans : ArrayList, LinkedList, HashTable, HashMap and ConcurrentHashMap, etc.

All the Best for Interview !!!   



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