Java Hibernate is an object-relational mapping tool(ORM) allowing the mapping of object-oriented models to relational databases for web applications by providing a framework. Mapping of entities in a Java class to tables created in a database and mapping from Java data types to SQL data types is one of the primary functions of Hibernate. You can also inquire or retrieve data using Hibernate. It relieves the developer from manually handling the database.
Hibernate is the Object-Relational Mapping (ORM) framework in Java created by Gavin King in 2001. It simplifies the interaction of a database and the Java application being developed. It is an ORM tool that is powerful and lightweight. Another important thing is that this is an open-source high-performance tool. Hibernate implements Java Persistence API specifications and is a very powerful object-relational persistence and query service for applications developed in Java.
Hibernate Architecture:
Configuration : Generally written in hibernate.properties or hibernate.cfg.xml files. For Java configuration, you may find class annotated with @Configuration. It is used by Session Factory to work with Java Application and the Database. It represents an entire set of mappings of an application Java Types to an SQL database.
The Configuration object provides two keys components −
Database Connection − This is handled through one or more configuration files supported by Hibernate. These files are hibernate.properties and hibernate.cfg.xml.
Class Mapping Setup − This component creates the connection between the Java classes and database tables.
Session Factory : Any user application requests Session Factory for a session object. Session Factory uses configuration information from above listed files, to instantiates the session object appropriately.
Session : This represents the interaction between the application and the database at any point of time. This is represented by the org.hibernate.Session class. The instance of a session can be retrieved from the SessionFactory bean.
Query : It allows applications to query the database for one or more stored objects. Hibernate provides different techniques to query database, including NamedQuery and Criteria API.
First-level cache : It represents the default cache used by Hibernate Session object while interacting with the database. It is also called as session cache and caches objects within the current session. All requests from the Session object to the database must pass through the first-level cache or session cache. One must note that the first-level cache is available with the session object until the Session object is live.
Transaction : enables you to achieve data consistency, and rollback incase something goes unexpected.
Persistent objects : These are plain old Java objects (POJOs), which get persisted as one of the rows in the related table in the database by hibernate.They can be configured in configurations files (hibernate.cfg.xml or hibernate.properties) or annotated with @Entity annotation.
Second-level cache : It is used to store objects across sessions. This needs to be explicitly enabled and one would be required to provide the cache provider for a second-level cache. One of the common second-level cache providers is EhCache.
Hibernate Features:
1. Lightweight
Hibernate is a lightweight framework as it does not contains additional functionalities; it uses only those functionalities required for object-relational mapping.
It is a lightweight framework because it uses persistent classes for data transfer between java application and databases.
2. Open Source
Hibernate is open-source software that means it is available for everyone without any cost. Its source code is made available so that anyone can use and develop applications using hibernate.
It can be downloaded from its official website, hibernate.org. The latest version a user can download is Hibernate 5.4.
3. ORM (Object Relation Mapping)
Hibernate is an ORM tool which helps in the interaction between the java classes and relational database.
It also solves the problem of data mismatch found in Java application and RDBMS.
4. High Performance
Hibernate supports many different fetching techniques such as, caching, lazy initialization, and many more to achieve high performance.
5. HQL (Hibernate Query Language)
Hibernate has its query language, i.e., HQL (Hibernate Query Language) which is independent of the database.
HQL is an object-oriented language similar to SQL, but it works with the persistent object and its properties.
6. Caching
Hibernate supports two levels of caching, first-level and second-level caching.
Caching is the process of storing data into cache memory and improves the speed of data access.
7. Auto-Generation
Hibernate provides a feature of automatic table generation. It means a programmer need not worry about the query implementation, i.e., Hibernate does on its own.
8. Scalability
Hibernate is highly scalable as it can be fit in any environment. Hibernate can be used for both small scale and large scale applications.
9. Lazy Loading
Hibernate supports a new concept called lazy loading. Lazy loading concept retrieves the only necessary object for execution.
It also improves the performance of an application.
10. Easy to learn
Hibernate is easy to learn and implement. It is developer-friendly as it takes care of the changes made to the database automatically, so it reduces the developer’s work.
11. Database Independent
Hibernate is database-independent as it provides ‘Database Dialect’ so we need not write SQL queries.
It supports many databases such as Oracle, MySql, Sybase, etc.
Advantages of Java Hibernate
High Yielding: If an application is implemented with the help of JDBC, one of the biggest challenge faced is the time that is spent in developing, tuning and maintaining the code that is relevant to JDBC. The answer to this is ORM. By using ORM, the time taken by an application to be implemented decreases exponentially as there is no need to examine the code and mapping mechanism. The database is efficiently managed by a robust, ready and totally trusted ORM engine.
Well Structured: ORM has an effective design pattern which is put into effect and tested well. It does not require redoing an already completed task which is also tried, tested and is being used again thus saving time.
Advantages of Hibernate
Hibernate is better then plain JDBC: You can use Hibernate which generates the SQL on the fly and then automatically executes the necessary SQL statements. This saves a lot of development and debugging time of the developer. Writing JDBC statement, setting the parameters, executing query and processing the result by hand is lot of work. Hibernate will save all tedious efforts.
Mapping of Domain object to relational database: Hibernate maps your domain object with the relational database. Now you can concentrate on your business logic rather than managing the data in database.
Layered architecture: Hibernate is layers architecture and you can use the components as per your application need.
JPA Provider: Hibernate can work as JPA provider in JPA based applications.
Standard ORM: Hibernate is standard ORM solutions and it also supports JPA.
Database Independent: Hibernate is database independent and you can use any database of your choice.
Caching Framework: There are many caching framework that works with Hibernate. You can use any one in your application to improve the performance of your application.
Disadvantages of Hibernate
Lots of API to learn: A lot of effort is required to learn Hibernate. So, not very easy to learn hibernate easily.
Debugging: Sometimes debugging and performance tuning becomes difficult.
Slower than JDBC: Hibernate is slower than pure JDBC as it is generating lots of SQL statements in runtime.
Not suitable for Batch processing: It advisable to use pure JDBC for batch processing.
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