Monday, 2 February 2015

Hibernate Interview Questions and Answers (Part2)

11. What is a hibernate xml mapping document and how does it look like?
In order to make most of the things work in hibernate, usually the information is provided in an xml document. This document is called as xml mapping document. The document defines, among other things, how properties of the user defined persistence classes’ map to the columns of the relative tables in database.
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC
   <class name="sample.MyPersistanceClass" table="MyPersitaceTable">
      <id name="id" column="MyPerId">          <generator class="increment"/>
      <property name="text" column="Persistance_message"/>
      <many-to-one name="nxtPer" cascade="all" column="NxtPerId"/>
Everything should be included under <hibernate-mapping> tag. This is the main tag for an xml mapping document.

12. Show Hibernate overview?
13. What the Core interfaces are of hibernate framework?
There are many benefits from these. Out of which the following are the most important one.
i. Session Interface – This is the primary interface used by hibernate applications.
The instances of this interface are lightweight and are inexpensive to create and destroy.
Hibernate sessions are not thread safe.
ii. SessionFactory Interface – This is a factory that delivers the session objects to hibernate application. Generally there will be a single SessionFactory for the whole application and it will be shared among all the application threads.
iii. Configuration Interface – This interface is used to configure and bootstrap hibernate. The instance of this interface is used by the application in order to specify the location of hibernate specific mapping documents.
iv. Transaction Interface – This is an optional interface but the above three interfaces are mandatory in each and every application. This interface abstracts the code from any kind of transaction implementations such as JDBC transaction, JTA transaction.
v. Query and Criteria Interface – This interface allows the user to perform queries and also control the flow of the query execution.

14. What are Callback interfaces?
These interfaces are used in the application to receive a notification when some object events occur. Like when an object is loaded, saved or deleted. There is no need to implement callbacks in hibernate applications, but they’re useful for implementing certain kinds of generic functionality.

15. What are Extension interfaces?
When the built-in functionalities provided by hibernate is not sufficient enough, it provides a way so that user can include other interfaces and implement those interfaces for user desire functionality. These interfaces are called as Extension interfaces.

16. What are the Extension interfaces that are there in hibernate?
There are many extension interfaces provided by hibernate.
 ProxyFactory interface - used to create proxies
 ConnectionProvider interface – used for JDBC connection management
 TransactionFactory interface – Used for transaction management
 Transaction interface – Used for transaction management
 TransactionManagementLookup interface – Used in transaction management.
 Cahce interface – provides caching techniques and strategies
 CacheProvider interface – same as Cache interface
 ClassPersister interface – provides ORM strategies
 IdentifierGenerator interface – used for primary key generation
 Dialect abstract class – provides SQL support

17. What are different environments to configure hibernate?
There are mainly two types of environments in which the configuration of hibernate application differs.
i. Managed environment – In this kind of environment everything from database connections, transaction boundaries, security levels and all are defined. An example of
this kind of environment is environment provided by application servers such as JBoss,
Weblogic and WebSphere.  ii. Non-managed environment – This kind of environment provides a basic configuration template. Tomcat is one of the best examples that provide this kind of environment.

18. What is the file extension you use for hibernate mapping file?
The name of the file should be like this : filename.hbm.xml
The filename varies here. The extension of these files should be “.hbm.xml”.
This is just a convention and it’s not mandatory. But this is the best practice to follow this extension.

19. What do you create a SessionFactory?
Configuration cfg = new Configuration();
cfg.setProperties( System.getProperties() );
SessionFactory sessions = cfg.buildSessionFactory();
First, we need to create an instance of Configuration and use that instance to refer to the location of the configuration file. After configuring this instance is used to create the SessionFactory by calling the method buildSessionFactory().

20. What is meant by Method chaining?
Method chaining is a programming technique that is supported by many hibernate interfaces. This is less readable when compared to actual java code. And it is not
mandatory to use this format. Look how a SessionFactory is created when we use method chaining.
SessionFactory sessions = new Configuration()
    .setProperties( System.getProperties() )
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