In -depth interpretation of Persistence API framework technical principles in the Java class library

The Persistence API (referred to as JPA) in the Java class library is a framework technology that is used to simplify the interaction between Java applications and databases.This article will in -depth interpretation of the technical principles of the JPA framework and provide the necessary programming code and related configuration description. 1. Introduction to JPA framework: The JPA framework is one of the implementation of the Java Persistence specification. It provides a set of APIs and tools that allows Java developers to operate databases in an object -oriented manner.The core goal of the JPA framework is to simplify the development of the data access layer and improve the maintenance of development efficiency and code. Second, the technical principle of the JPA framework: 1. The creation and mapping of the physical class: In the JPA framework, it is necessary to create a physical class, and the physical class is used to represent the table in the database.Each entity class usually corresponds to a table in the database, and the attribute in the class corresponds to the column in the table.By using annotations (such as@Entity,@Table,@Column, etc.), the physical class and the database table can be mapped. 2. The implementation of database operations: The JPA framework provides a standard API that can use these APIs for common database operations, such as adding, deletion, modification, etc.By calling the EntityManager object, you can perform continuous, merged, deleted, and query.Developers can operate the database through object -oriented way without writing the original SQL statement. 3. Affairs management: The JPA framework has built -in transaction management functions to ensure the consistency and integrity of the data.Affairs is a series of logic units for operations. JPA provides support for transactions through the EntityTransAction interface.Developers can manage transactions by calling methods such as Begin (), Commit (), and Rollback () of the transaction. 4. Query language jql: The JPA framework introduces a query language jql (Java Persistence Query Language), which can query data in the database through the jql statement.The jql statement is similar to the SQL statement, but it is more object -oriented.Through the JQL query statement, complex database query operations can be easily performed. Third, the code and configuration description of the JPA framework: 1. The creation and mapping of the physical class: The following is a simple physical category sample code: @Entity @Table(name = "user") public class User { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id; @Column(name = "username") private String username; // omit the definition of other attributes and methods } 2. The implementation of database operations: Here are a sample code that uses JPA for database operations: // Get EntityManager instance EntityManagerFactory factory = Persistence.createEntityManagerFactory("persistence-unit-name"); EntityManager entityManager = factory.createEntityManager(); // Open transaction EntityTransaction transaction = entityManager.getTransaction(); transaction.begin(); // New users User user = new User(); user.setusername ("Zhang San"); entityManager.persist(user); // Query the user User queriedUser = entityManager.find(User.class, 1L); System.out.println ("Username:" + QueriedUser.getUsername ()); // Submit a transaction transaction.commit(); // Close EntityManager and EntityManagerFactory entityManager.close(); factory.close(); 3. Related configuration: The JPA framework needs to perform some related configurations in the configuration file, such as data source configuration, ORM configuration, etc.The following is a typical example of Persistence.xml configuration file: <?xml version="1.0" encoding="UTF-8"?> <persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd" version="2.0"> <persistence-unit name="persistence-unit-name" transaction-type="RESOURCE_LOCAL"> <properties> <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/> <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/mydb"/> <property name="javax.persistence.jdbc.user" value="root"/> <property name="javax.persistence.jdbc.password" value="password"/> <!-Other configuration attributes-> </properties> </persistence-unit> </persistence> The above is an in -depth interpretation of the technical principles of the Persistence API framework in the Java library. At the same time, it provides example code and related configuration descriptions.By using the JPA framework, Java developers can more easily perform database operations to improve development efficiency and code quality.