Top 40 Hibernate Interview Questions and Answers

Hibernate Interview Questions and Answers

The demand for Hibernate skills remains significant in the current job market as it has a strong foundation in Java, ORM Popularity, support enterprise applications, and support legacy systems. Explore our Hibernate course syllabus to enhance your Java application development. 

Hibernate Framework Interview Questions and Answers

1. Define Hibernate.

Hibernate is a lightweight, object-relational mapping (ORM) framework for Java that is available as open source software. By mapping Java classes to database tables and their properties to columns, it makes interacting with relational databases easier. 

2. Describe the main advantages of Hibernate.

Some of the key benefits of Hibernate are,

• Reduced development time: Since the majority of the JDBC boilerplate code (such as connection handling, SQL creation, and result set mapping) is automated.
• Enhanced productivity: puts developers’ attention on business logic rather than intricate database operations.
• Better code maintainability: By separating business logic from object-relational mapping logic, code becomes more modular and adaptable.
• Portability: Requires little code modification to operate with a variety of databases, including MySQL, Oracle, and PostgreSQL.
• Lazy loading: By retrieving related things only when they are truly needed, lazy loading enhances performance. 

3. Explain an ORM framework.

A programming approach known as ORM (Object-Relational Mapping) links tables in a relational database to objects in an object-oriented programming language, such as Java. It fills the gap between the relational database paradigm and the object-oriented paradigm. 

4. Explain the core concepts of Hibernate.

The core concepts of Hibernate are

• Session: A single unit of work with the database is represented by a session. Object creation, reading, updating, and deletion fall under its purview.
• SessionFactory: The thread-safe factory that generates Session objects is called SessionFactory.
• Transaction: A work unit that is either committed or completely rolled back.
• Mapping Files or Annotations: Specify how Java classes are mapped to database tables in mapping files (or annotations).
• Query Language: Hibernate’s own object-oriented query language, Query Language (HQL), is comparable to SQL but focuses on objects. 

5. State the difference between Session and SessionFactory.

6. Explain the Hibernate architecture.

The architecture of Hibernate is as follows:

• Configuration: Hibernate configuration properties, such as dialect and database connection information, are loaded.
• SessionFactory: Session objects are created by the SessionFactory.
• Session: Oversees the database interaction for a particular work unit.
• Transaction: A transaction is a unit of work that can be rolled back or committed.
• JDBC: To communicate with the underlying database, use JDBC.

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7. Describe the various methods that Hibernate can map Java classes to database tables.

• XML mapping files: Use XML tags to define mappings.
• Annotations: To define mappings, use Java annotations right inside the Java class. 

8. What are the different types of mappings in Hibernate?

• One-to-one: Assigns a single object to a single object in a different table.
• One-to-many: Assigns a single item to several items in a different table.
• Many-to-one: Multiple objects are mapped to a single object in another table using the many-to-one mapping method.
• Many-to-many: Multiple objects are mapped to multiple objects in another table using the many-to-many mapping function.

9. Describe how to use Hibernate to map a group of items.

• To represent the collection in your Java program, use collections such as Set, List, or Map.
• Add the relevant Hibernate annotation (such as @OneToMany or @ManyToMany) to the collection property.
• In the annotation, include the join table and additional mapping information. 

10. Define HQL.

An object-oriented query language called Hibernate Query Language is used to communicate with Hibernate objects. Though it emphasizes object-oriented notions, it is comparable to SQL. 

11. What benefits does HQL offer over SQL?

• Object-oriented: HQL queries are easier to interpret and manage since they concentrate on objects and their relationships.
• Portable: Your program is more portable since HQL queries are independent of databases.
• Integration with Hibernate: Better performance and simpler integration with other Hibernate capabilities are made possible by HQL’s close integration with Hibernate. 

12. How are HQL queries run in Hibernate?

• To build a Query object, use the createQuery() function of the Session object.
• Use the setParameter() function to set the query’s parameters.
• Use functions like list(), uniqueResult(), and others to run the query.

13. What does Hibernate’s caching mean?

Caching enhances performance by storing frequently accessed items in memory. Both first-level (session-level) and second-level (application-level) caching are offered by Hibernate. 

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14. Explain the difference between first-level and second-level cache in Hibernate.

15. How can you set up Hibernate’s second-level cache?

• Incorporate a caching provider into your Hibernate setup.
• Use XML or annotations to set up caching for particular entities or collections. 

16. Explain a transaction in Hibernate.

In Hibernate, a transaction is a work unit linked to a session that controls modifications in one or more systems.

• Transaction boundaries: Establish the beginning and ending of a sequence of actions that need to be finished or reversed. 
• Transaction management: It encompasses techniques for committing, reversing, and monitoring a transaction’s progress. 
• Transaction goals: Assign attributes such as durability, isolation, consistency, and atomicity to the asset. 

Hibernate Interview Questions and Answers for Experienced

17. How do you manage transactions in Hibernate?

Transactions can be started, committed, and rolled back using the Transaction interface. In Hibernate, transactions can be managed in the following ways:

• Begin a transaction: To initiate a new transaction, use the begin() method.
• Commit a transaction: To terminate a transaction and clear the related session, use the commit() method. This guarantees that modifications are stored in the database.
• Roll back a transaction: To reverse the current transaction, use the rollback() method.
• Configure a timeout for transactions: To set a timeout for upcoming calls to begin(), use the setTimeout(int seconds) function.
• Verify whether a transaction is active: To find out if a transaction is still active, use the isActive() method.

18. Describe the various Hibernate transaction isolation levels.

The various transaction isolation levels in Hibernate are as follows:

• READ_UNCOMMITTED: The lowest degree of isolation, READ_UNCOMMITTED, allows for the reading of uncommitted data.
• READ_COMMITTED: Prevents unclean reads, however it may still come across phantom and non-repeatable reads.
• REPEATABLE_READ: May encounter phantom reads but prevents dirty and non-repeatable reads.
• SERIALIZABLE: The highest level of isolation, which stops all abnormalities but can have a big effect on performance.

19. How can you improve Hibernate performance?

The performance of Hibernate can be improved by

• Using Caching: Put first-level or second-level caching into practice.
• Optimizing queries: Steer clear of pointless database calls and use effective HQL queries.
• Lazy loading: Only retrieve related objects when required.
• Batching: It is the process of carrying out several operations (such inserts and updates) in a single batch.
• Connection pooling: Reduce overhead by reusing database connections. 

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20. Which Hibernate applications frequently experience performance bottlenecks?

N+1 selects problem: occurs when a single object is the subject of several queries that are run to retrieve related objects.

Overuse of database calls: It can happen as a result of ineffective searches or inadequate caching.

Transaction contention: When several transactions vie for the same resources, this is known as transaction contention.

21. How do Spring and Hibernate work together?

Hibernate Sessions and transactions may be easily configured and managed with Spring.

Simple SQL queries can be run using Spring’s JdbcTemplate.

Transaction management is made easier with Spring’s @Transactional annotation.

Hibernate Interview Questions for Senior Developers

22. In Hibernate, what is a disconnected object?

Disconnected object is something that isn’t connected to a session anymore. It is a detached object’s modifications that are not immediately saved to the database.

23. How may an object that has been disconnected from a session be reattached?

An object that has been disconnected from a session can be reattached using the update() or merge() methods of the Session object.

24. In Hibernate, what is optimistic locking?

Optimistic locking is a technique for avoiding lost updates. It is a version number is given to every object. The version number is increased whenever an object is updated. The update is denied if the object’s version number has changed since it was last read. 

25. What does Hibernate’s pessimistic locking mean?

Pessimistic locking in Hibernate is a method that stops concurrent access to data by using database-level locks. It has less lenient than optimistic locking.

26. Describe the Hibernate implementation of custom types.

Developers can map fields in an entity to SQL types that don’t suit the conventional Java-to-SQL data types in Hibernate by using custom types. 

The @Type annotation allows developers to define the custom type class that Hibernate should use when mapping a field to a database column in order to construct custom types.

Other types of hibernation include:

• Primitive types: “Integer,” “character,” “float,” “string,” “double,” “Boolean,” “short,” and “long” are some examples of these data types.
• Binary and large object types: “Clob,” “blob,” “binary,” and “text” are some of these. 

27. Which Hibernate exceptions are frequently encountered?

• The base class for all Hibernate exceptions is called HibernateException.
• When there is an optimistic locking violation, the StaleStateException is thrown.
• When an object cannot be located in the database, an ObjectNotFoundException is raised.
• When something goes wrong when working with the database, the DataAccessException is thrown.

28. What is JPA?

The Java Community Process established the Java Persistence API (JPA) specification. It offers a common interface for Java object-relational mapping. One of the most widely used implementations of the JPA specification is Hibernate. 

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Hibernate Interview Questions for Senior Developers

29. What advantages does JPA offer?

The advantages of JPA are,

Vendor independence: It is easier to port JPA applications between various JPA implementations.

Standardization: Offers a shared set of object-relational mapping principles and APIs.

Improved code readability: JPA makes use of annotations and a well-known object-oriented methodology. 

30. What connection does Hibernate have to JPA?

A completely compliant implementation of the JPA specification is Hibernate. By setting up Hibernate to use the JPA API, you can use it as a JPA provider. 

31. In what ways does Spring make Hibernate development easier?

It offers a practical method for setting up and controlling Hibernate sessions and transactions. It uses the @Transactional annotation to provide features like declarative transaction management. It works well with dependency injection and other Spring components. 

32. What function does Spring’s SessionFactory serve?

• Spring’s LocalSessionFactoryBean creates and maintains the SessionFactory.
• Configuring and obtaining a SessionFactory instance is made easy with Spring.

33. How are Hibernate applications tested?

Hibernate application will be tested as follows:

• Make use of a testing framework such as TestNG or JUnit.
• For testing purposes, create a distinct test database.
• To simulate dependencies like the SessionFactory, use mocking frameworks (like Mockito).
• Create unit tests for each entity and the mappings between them.
• To test how Hibernate interacts with other components of the application, write integration tests. 

34. How can applications that use hibernation be secured?

We can secure Hibernate applications as follows:

• Make use of appropriate authorization and authentication procedures.
• Use prepared statements or parameterized queries to avoid SQL injection attacks.
• Verify and clean user input.
• To limit access to sensitive data, put in place the proper access control measures. 

35. How can Hibernate entities be made available as RESTful resources?

Hibernate entities can be made available as RESTful resources as follows:

• To construct RESTful web services, use frameworks such as Jersey or Spring Boot.
• To serialize and deserialize objects, use object-to-XML or object-to-JSON libraries (like Jackson or JAXB).
• Put the right security measures in place to safeguard your RESTful endpoints. 

36. How can a microservices architecture make use of Hibernate?

Microservice architecture will use Hibernate as follows:

• Every microservice has the ability to have its own Hibernate configuration and database.
• To communicate between microservices, use lightweight protocols like REST and gRPC.
• To increase performance, think about implementing a distributed caching solution. 

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37. In Hibernate, what is a read-only session?

A Session optimized for read-only tasks. It can enhance the performance of programs that require a lot of reading. 

38. Explain filter in Hibernate.

In Hibernate, a filter is a named, parameterized, global filter that may be turned on or off for a particular Hibernate session. Although filters are parameterized within the application, they can be utilized in a manner akin to that of database views.

The following definitions apply to filters:

• Annotations: Alternatively, use @org.hibernate.annotations.FilterDef.FilterDefs
• Mapping files: Within an element, use the element.

Multiple collections and/or entities, each with its own condition, can have a filter applied to them. can be used to define a default condition. When the filter is attached to something without a condition specified, this default condition will be applied.  

39. Explain how to use event listeners in Hibernate.

To intercept distinct phases of an entity’s lifecycle, Hibernate provides a variety of event listener interfaces. Here are a few of them: 

• PreInsertEventListener: Before an entity is added to the database, events are intercepted. 
• PostInsertEventListener: After an entity is added to the database, the PostInsertEventListener is triggered.

40. What are some best practices for using Hibernate?

Here are some best practices for using Hibernate framework in Java applications:

• Employ caching: Caching is a performance-enhancing approach that involves storing frequently requested data in memory.
  • Hibernate provides caching for collections, queries, and entities.
• Select the appropriate mappings: For a high-performance data access layer, the appropriate mappings are crucial.
  • There are a lot of options available, but not all of them are equally good in terms of performance.
• Steer clear of n+1 queries: An application that uses N+1 database queries to retrieve a set of N entities is said to be experiencing the N+1 select problem. Use JPQL queries to retrieve related entities in a single query to get around this.
• Put a no-argument constructor into practice: A public or protected no-arg constructor is required for the entity class. There may be additional constructors for the entity class.
• Make use of named queries: Hibernate offers named queries that may be used throughout the code and defined centrally.
• Decrease query selectivity: One performance recommended practice is to decrease query selectivity.
• Record SQL statements: One of the best practices for performance is to log SQL statements. 

Conclusion

We hope that this list of top 40 Hibernate interview questions and answers gives you a thorough understanding of Hibernate! Gain expertise with Java application development with our Hibernate training in Chennai.