Jakarta Persistence API framework in the Java Class Library Frequently Asked Questions Answers
The Jakarta Persistence API (JPA) is a framework for achieving the object's persistence in Java applications.It provides a simple and intuitive way to map the Java object to the database table, thereby persisting the data into the database.Here are some common questions and answers to the Jakarta Persistence API framework:
Question 1: What is Jakarta Persistence API?
Answer: Jakarta Persistence API is a specification for object-relationship mapping (ORM) in Java.It allows developers to operate the database in an object -oriented manner instead of writing SQL query statements.
Question 2: How to configure the JPA framework?
Answer: The configuration of the JPA framework requires a Persistence.xml file, which contains information such as data source configuration and physical category mapping.The following is a persistence.xml file of an example:
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd"
version="2.2">
<persistence-unit name="myPersistenceUnit" transaction-type="RESOURCE_LOCAL">
<class>com.example.User</class>
<properties>
<property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/mydb?useSSL=false"/>
<property name="javax.persistence.jdbc.user" value="root"/>
<property name="javax.persistence.jdbc.password" value="password"/>
</properties>
</persistence-unit>
</persistence>
Question 3: How to define the physical class?
Answer: In JPA, the physical class is used to represent the table in the database.The following is the definition of the user entity class of an example:
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
@Entity
public class User {
@Id
private Long id;
private String name;
// getters and setters
}
Question 4: How to perform query operations?
Answer: In JPA, you can use the EntityManager object to perform the query operation.The following is the code of the query operation of an example:
import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;
import java.util.List;
public class Main {
public static void main(String[] args) {
EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("myPersistenceUnit");
EntityManager entityManager = entityManagerFactory.createEntityManager();
List<User> userList = entityManager.createQuery("SELECT u FROM User u", User.class).getResultList();
for (User user : userList) {
System.out.println(user.getName());
}
entityManager.close();
entityManagerFactory.close();
}
}
Question 5: How to perform update operations?
Answer: In JPA, you can use the EntityManager object to perform the update operation.The following is the code of an example of an example:
import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;
public class Main {
public static void main(String[] args) {
EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("myPersistenceUnit");
EntityManager entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
User user = entityManager.find(User.class, 1L);
user.setName("New Name");
entityManager.getTransaction().commit();
entityManager.close();
entityManagerFactory.close();
}
}
These are some common questions and answers, I hope to help you.You can start using the Jakarta Persistence API framework based on this information.
