Hibernate interview questions, Hibernate, Interview, Questions

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Tags/Keywords : Hibernate interview questions, Hibernate, Interview, Questions
Author : Amit
Date (Year/Month/Date): 2009-03-31 Hibernate Question : Can the strategy of LAZY load for the dependent domain classes, be change once SessionFactory is created? Answer to the Best of my knowledge: No, as SessionFactory is loaded/created once for the entire lifecycle of the application,and while creating Hibernate SessionFactory, appropriate HBM XML file is read and these configuration are used for creating or instantiating Hibernate SessionFactory, so it is logically not possible as, SessionFactory is not going to refresh but destroyed and recreated. And for different modules from the same application, if requires LAZY as true / false, then using a single Hibernate SessionFactory won't be able to serve both these Persistent Object loading strategies.

Books/References :

Hibernate Interview Questions 1:

Does Hibernate Session Object has any cache associated with it by default ?

Hibernate Interview Answer 1:

Yes, first-level caching is a mandatory requirement for Hibernate Session Object.

Hibernate Interview Questions 2:

Is there any cache associated with Hibernate SessionFactory Object?

Hibernate Interview Answer 2:

Yes, there is an optional second-level cache with Hibernate SessionFactory
object.

Hibernate Interview Questions 3:

Can a single Hibernate Session object be used across multiple threads 
running within a process

Hibernate Interview Answer 3:

No, Hibernate Session is basically single-threaded and not to be used across
multiple threads.

Hibernate Interview Questions 4:

Is this same for Hibernate SessionFactory object as well?

Hibernate Interview Answer 4:

No, Hibernate SessionFactory is basically thread-safe, thus can be re-used 
across multiple threads and multiple Transacions as well.

Hibernate Interview Questions 5:

How can the second-level caching for Hibernate SessionFactory object be
disabled?



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Hibernate Interview Answer 5:

By setting appropriate hibernate.cache configuration related properties, one
can enable/disable second-level caching for Hibernate SessionFactory object
but only for once before SessionFactory is created

Hibernate Interview Questions 6:

Is it possible to use Hibernate Session object with the scope and context
defined by JTA Transaction ?

Hibernate Interview Answer 6:

Yes, starting with Hibernate 3.0.1 version, Sessionfactory.getCurrentSession method
has the scope and context defined by the running JTA Transaction scope and context.
But as of Hibernate 3.1 version, getCurrentSession method of Hibernate
SessionFactory has the current Session Scope and Context controlled by pluggable
current Session Context class, defined in configuration parameter such as 
hibernate.current_session_context_class.

Hibernate Interview Questions 7:

As of Hibernate 3.1 version can you be able to explain how many ways
scope and context of Hibernate current contextual session be handled?

Hibernate Interview Answer 7:

As of Hibernate 3.1 version, Hibernate has three ways to handle current contextual
session, such as
JTASessionContext
ThreadLocalSessionContext
ManagedSessionContext.

Hibernate Questions with answer as of 19th Jan 2010 :

Hibernate Interview Questions 1 :
What is the difference between class tag and component tag in Hibernate
from the persistence perspective?

Hibernate Interview answer 1 :
class tag refers to an Entity that is persisted with an identifier, 
while component tag means the POJO associated with component tag is
persisted along with contained object as a value type.So it doesn't require
an identifier, while the contained object has an entity reference, not for the 
component object.

Hibernate Interview Questions 2 :
What is the difference between component and dynamic component?

Hibernate Interview answer 2 :
Component in Hibernate world, means something that is embeded in
a contained object and there exist a composition style of binding between
the contained object and the component object. So component is declared
inside a class tag, just to say one type of use.
Dynamic-component has the same characteristics as component but there exists
a difference in the way dynamic-component can be used to map a bean's attribute, 
this can be of type java.util.Map with the key defined in mapping file
and corresponding value from the table's column.
So with dynamic-component, there can be possibility of changing the attribute
key/value pair during deployment time, just by changing the name and 
column values in the mapping configuration file.



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|-Hibernate Question 1: | Can a Hibernate Session, that is retrieved/created from a Hibernate | SessionFactory, be shared across multiple concurrent Thread/Requests? | |-Hibernate Answer No, as Hibernate Session is not Thread-Safe, so sharing it with multiple concurrent Thread of execution or request will have concurrentcy issues. It is always better to use a single Hibernate Session for a single transaction, that means as long as the transaction is running or not commited, a single session can be used. As a Transaction is running in isolation for each Thread or request. |-Hibernate Question 2: | What is a good approach of handling Hibernate Session, in case of | any database exception or Hibernate Exception that is occuring | while a Hibernate Session is in use? | |-Hibernate Answer As Hibernate Session caches Persistent Object, in case of any Database exception or Hibernate Exception occuring, then Session cache might have some stale data or Persistent Object not in sync with Database. So it is always better to rollback Transaction, close Session, in this circumtances. |-Hibernate Question 3: | How Hibernate manages Transaction timeout in Managed and Non-managed | environments? | |-Hibernate Answer In Managed environment, that is JTA transaction can handle timeout, so Hibernate delegated Transaction timeout task to JTA Transaction. But in non-managed environment, Developer has to explicitly specify Transaction timeout parameter while using Transaction from Hibernate Session by using setTimeOut(time in seconds). But this feature cannot be fully compared with JTA based Transaction timeout operation. Any one wants to comment on these questions and answer, please do so.

Hibernate Question: Question 1 : What is the first level cache and the second level cache in Hibernate? Answer 1: First level cache is associated with Hibernate Session object, and is mandatory, while second level cache is optionally associated with Hibernate SessionFactory instance. Question 2: Which cache is cluster-level, first level or second level? Answer 2: Second level cache is optional, but can be cluster-level. Question 3: How many different instance states exist for an instance of a persistent class while using Hibernate? Answer 3: There are three different instance states, such as Transient, Persistent, and detached. Questions 4: What are the instances having persistent entity? Answer 4: Persistent and detached instances are having persistent entity. Question 5: Can you please explain these three instance states with help of an example? Answer 5: Suppose in a web application, if a user information is passed from the registration page shwon on browser for the first time, then the UI helper class will be creating an instance of the User class, and populate all the relevant details onto the USER object. At this level USER object has a Java identity but no persistent identity. So this USER object is transient instance state. Then if this USER instance is sent to the business level, and with help of DAO, is stored in backend db, then this USER instance has got both Java and Persistent identities, so is having Persistent instance state. If this USER object is again sent to the UI level for displaying an edit screen, then this USER instance in UI tier is detached instance state, as is having both Java and persistent identity. But Hibernate cann't relate Java and persistent identities for detached instance states.

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