Introduction and User Guide to Jakarta Persistence API Framework of Jakarta Persistence API
Jakarta Persistence API (JPA) is the core ORM framework on the Java platform to simplify the interaction between developers and persistent data.This article will introduce the JPA framework, give us guidelines, and provide some Java code examples to help readers better understand and apply JPA.
## What is Jakarta Persistence API framework?
The Jakarta Persistence API framework is a open source ORM (object relationship mapping) specification. It aims to help developers more conveniently operate the database and mappore the state of the object with the database table.This specification is developed on the basis of the Java Persistence API (JPA) in Java Ee, and has been used in environments outside the Java Ee and Java SE, which can continue to develop.
The JPA framework provides a standard API, as well as a series of annotations and configuration files, so that developers can use objects to operate the database without writing SQL statements directly.
## jpa framework main feature
The JPA framework has the following main characteristics:
1. Object-Relationship mapping: The JPA framework is associated with the Java object with the table in the database through annotation or XML configuration to realize the conversion of the object and relationship.
2. Lazy load and delay loading: Developers can use lazy loading technology provided by the JPA framework to delay loading related objects to optimize system performance.
3. Affairs management: JPA framework supports transaction management. Developers can use annotations or programming to manage database transactions.
4. CRUD operation: The JPA framework provides a set of APIs for common CRUD operations, including creating, reading, updating, and deleting database records.
5. Query Language: JPA framework supports the use of JPQL (Java Persistence Query Language) for database query, which provides similar functions to SQL.
## How to use the JPA framework
The following is the general step of using the JPA framework:
### 1. Add dependence
First, in the construction tool of your Java project, such as Maven or Gradle, add the JPA framework dependency item.
Maven example:
<dependency>
<groupId>jakarta.persistence</groupId>
<artifactId>jakarta.persistence-api</artifactId>
<version>2.2.3</version>
</dependency>
### 2. Configure data source and database connection
In the project, you need to configure the database connection and data source information so that the JPA framework can be connected to the database.
### 3. Create a physical class
Before using the JPA framework, you need to create a physical class and perform corresponding annotations.The physical class is mapped to the database table, and the attributes of the object are mapped to the column of the table.
Example code:
@Entity
@Table(name = "users")
public class User {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "name")
private String name;
// Eliminate other attributes and methods
}
### 4. Write data access layer code
Use the JPA framework for data access to write data access layer code.You can create an interface, and then use JPA EntityManager or Jparepository for database operations.
Example code:
@Repository
public class UserRepository {
@PersistenceContext
private EntityManager entityManager;
public User findById(Long id) {
return entityManager.find(User.class, id);
}
public User save(User user) {
entityManager.persist(user);
return user;
}
public void delete(User user) {
entityManager.remove(user);
}
// Other methods omitted
}
### 5. Use JPA to perform data operation
Finally, you can use the JPA framework in business logic for data operation.For example, create, read, update and delete records.
@Service
@Transactional
public class UserService {
@Autowired
private UserRepository userRepository;
public User createUser(String name) {
User user = new User();
user.setName(name);
return userRepository.save(user);
}
public User getUser(Long id) {
return userRepository.findById(id);
}
public void deleteUser(Long id) {
User user = userRepository.findById(id);
userRepository.delete(user);
}
// Other methods omitted
}
The above is the basic steps and example code of the JPA framework.According to your specific needs, you can further learn the advanced characteristics of JPA, such as associated mapping, query, and so on.
I hope this article can help you understand the JPA framework and be able to apply it flexibly in actual development.I wish you success!
