Hibernate Interview Questions - Two

Q1. How properties of a class are mapped to the columns of a database table in Hibernate? 

Ans: Mappings between class properties and table columns are specified in XML file. 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 “http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd”>
<hibernate-mapping>
<class name=”sample.MyPersistanceClass” table=”MyPersitaceTable”>
<id name=”id” column=”MyPerId”> <generator class=”increment”/> </id>
<property name=”text” column=”Persistance_message”/>
<many-to-one name=”nxtPer” cascade=”all” column=”NxtPerId”/>
</class>
</hibernate-mapping>

Everything should be included under tag. This is the main tag for an xml mapping document.

Q2. What are the benefits of using Hibernate template?

Ans: The benefits of Hibernate Template are: 

Hibernate Template, which is a Spring Template class, can simplify the interactions with Hibernate Sessions. Various common functions are simplified into single method invocations. The sessions of hibernate are closed automatically. The exceptions will be caught automatically, and converts them into run time exceptions. 

Q3. What the Core interfaces are of hibernate framework?

Ans: 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.

Q4. What’s the usage of callback interfaces in hibernate?

Ans: 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.

Q5. What are Extension interfaces?

Ans: 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.

Q6. How can we use new custom interfaces to enhance functionality of built-in interfaces of hibernate?

Ans: We can use extension interfaces in order to add any required functionality which isn’t supported by built-in interfaces. 

Q7. What are the Extension interfaces that are there in hibernate?

Ans: There are many extension interfaces provided by hibernate.

• ProxyFactory interface - Used to create proxiesConnection 
• Provider interface – Used for JDBC connection management 
• TransactionFactory interface – Used for transaction management 
• Transaction interface – Used for transaction management 
• TransactionManagementLookup interface – Used in transaction management. 
• Cache 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 

Q8. What are different environments to configure hibernate?

Ans: 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.

Q9. What’s the usage of Configuration Interface in hibernate?

Ans: Configuration interface of hibernate framework is used to configure hibernate. It’s also used to bootstrap hibernate. Mapping documents of hibernate are located using this interface.