What’s inside magic in Spring Data JPA

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How does Spring-Data JPA work to bootstrap Hibernate ?

Highlevel diagram

Here is the diagram for high level overview of JPA strucutre.

Details explained

Generally if you included spring-boot-starter-data-jpa in your maven file, several default configuration will be loaded by conventions. LIsted as below:

1. One bean named entityManagerFactory will be loaded. By default, spring ORM framework provided one default implementation : org.springframework.orm.jpa.AbstractEntityManagerFactoryBean
2. Similar to most SpringBoot functionalities (such as JDBC, AppServer etc.), it will scan current class path to find one suitable provider via SPI (Service Provider Interface) . Each provider (if you want to implement your own provider), should implement interface PersistenceProvider. Essentially the implementation should implementation method createEntityManagerFactory to create new EntityManagerFactory.
3. SpringBoot provided the default implementation: SpringHibernateJpaPersistenceProvider ( at \org\springframework\orm\jpa\vendor\SpringHibernateJpaPersistenceProvider.java)
4. This would build a new EntityManagerFactoryBuilderImpl instance, which is one Hibernate class (under org\hibernate\jpa\boot\internal\EntityManagerFactoryBuilderImpl.java) , it build a new EntityManagerFactory.
5. Internally it will invoke SessionFactoryBuilder.build, which will create a new instance of SessionFactory. Usually an application has a single SessionFactory instance and threads servicing client requests obtain Session instances from this factory.
6. Then developers can chose to call SessionFactory.openSession to get a new Session object. This is the main runtime interface between a Java application and Hibernate. This is the central API class abstracting the notion of a persistence service. The lifecycle of a Session is bounded by the beginning and end of a logical transaction. (Long transactions might span several database transactions.) The main function of the Session is to offer create, read and delete operations for instances of mapped entity classes.
7. A typical transaction should use the following idiom:

Session sess = sessionFactory.openSession();
 Transaction tx;
 try {
     tx = sess.beginTransaction();
     //do some work
     ...
     tx.commit();
 }
 catch (Exception e) {
     if (tx!=null) tx.rollback();
     throw e;
 }
 finally {
     sess.close();
 }

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