Detailed explanation of Jakarta Persistence API in Java Library

Jakarta Persistence API (JPA) is a framework used in the Java library for object relationship mapping (ORM).It provides a simple and standard method that maps the Java object to the tables in the relationship database and the durable operations for these tables. The emergence of JPA is to solve the tedious and complexity of the traditional JDBC programming.Using JPA, developers can describe the mapping relationship between the object and the database table by annotating or XML configuration, thereby achieving the durable and retrieval of the data. The core of JPA consists of three parts: 1. Entity CLASSES: The physical class of JPA is an ordinary Java class to represent the physical object in the application.These entity classes describe the mapping relationship between the database table through annotations or XML configuration. 2. Entity Manager: The entity manager is an interface provided by JPA to manage the life cycle of the physical object.Through the physical manager, developers can complete the operation of data persistence, query, and update. 3. JPQL (Java Persistence Query Language): JPQL is a query language for JPA to query the database.It is similar to SQL, but has nothing to do with the database.Developers can use JPQL query statements to retrieve and operate entity objects. The following is a simple example, which shows how to use JPA for the persistence and query operation of the object: // Import jpa -related classes import javax.persistence.*; // Define a physical class @Entity @Table(name = "employees") public class Employee { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; private String name; private String designation; // Construction method, Getter and Setter method ... } // Define the class of a management entity object public class EntityManagerExample { // Define the physical manager factory private static final EntityManagerFactory emf = Persistence.createEntityManagerFactory("my-persistence-unit"); public static void main(String[] args) { // Create a physical manager EntityManager em = emf.createEntityManager(); // Open transaction EntityTransaction tx = em.getTransaction(); tx.begin(); // Create a physical object Employee employee = new Employee(); employee.setName("John Doe"); employee.setDesignation("Software Engineer"); // Express the physical object to the database em.persist(employee); // Submit a transaction tx.commit(); // Turn off the physical manager em.close(); } } In the above examples, we first define a `Employee" physical class, and use annotations `@Entity` and@Table` to describe the mapping relationship between it and the database table.Then, a solid manager was created in the API of JPA in the `EntityManageRexample`, and the object of the` Employee` is persisted to the database by it. In short, Jakarta Persistence API provides a simple and standard way to achieve object relationship mapping for Java developers.Through JPA, developers can make databases more easily to improve development efficiency.