Introduction and application example of Jakartaee API framework in the Java class library
Jakarta EE (formerly known as Java EE) is a set of APIs and specifications for the construction of an enterprise -level Java application.It provides many powerful and widely verified APIs that can simplify the work of developers when building large -scale, high -performance applications.This article will briefly introduce the Jakarta EE API framework and provide some application instances.
1. Introduction
The Jakarta EE API framework consists of a series of Java APIs that can be used to develop distributed and scalable enterprise applications.It is built on the basis of Java SE (Standard Edition) and provides some additional APIs and specifications.Jakarta Ee provides many APIs for developing web applications, database access, message transmission, transaction processing, etc., such as Servlet, JPA (Java persistence API), JMS (Java message service), etc.
Jakarta EE organizes its API in a modular way and uses the Java EE container to provide the operating environment.The container is responsible for managing the life cycle, processing requests and response, and providing security and transaction management of the application.Common Java EE containers include Tomcat, Wildfly, Glassfish, etc.
2. Application instance
Here are some applications that use the Jakarta EE API framework and the corresponding Java code example:
1. Create a simple server
@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<body>");
out.println("<h1>Hello, Jakarta EE!</h1>");
out.println("</body>");
out.println("</html>");
}
}
In the above example, we created a simple server. When the client issued a GET request, it returned a HTML response, which contains a greeting message.
2. Use JPA to perform database access
@Entity
@Table(name = "employees")
public class Employee {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(name = "name")
private String name;
// omit other attributes and methods
// getter and setter method
}
@Stateless
public class EmployeeService {
@PersistenceContext(unitName = "myPU")
private EntityManager em;
public List<Employee> getAllEmployees() {
TypedQuery<Employee> query = em.createQuery("SELECT e FROM Employee e", Employee.class);
return query.getResultList();
}
// Other CRUD operation methods
}
The above code example shows how to use JPA (Java persistence API) for database access.We define an Employee entity class that uses annotations to maximize the entity and database table, and then create an EmployeeService.
3. Use JMS for message transmission
@Stateless
public class MessageProducer {
@Resource(lookup = "java:/jms/queue/MyQueue")
private Queue messageQueue;
@Inject
private JMSContext context;
public void sendMessage(String message) {
context.createProducer().send(messageQueue, message);
}
}
@MessageDriven
public class MessageConsumer implements MessageListener {
@Override
public void onMessage(Message message) {
if (message instanceof TextMessage) {
try {
String text = ((TextMessage) message).getText();
System.out.println("Received message: " + text);
} catch (JMSException e) {
e.printStackTrace();
}
}
}
}
The above code example shows how to use the JMS (Java message service) for message transmission.We created a MESSAGEPRODUCER stateless session bean, which sends the message to the JMS queue called "Myqueue".At the same time, we created a MessageConsumer message drive Bean, which monitor the message on the queue and process it when receiving the message.
Summarize:
This article briefly introduces the Jakarta EE API framework and its applications in enterprise -level Java applications.By providing rich APIs and specifications, Jakarta EE simplifies the work of developers to build high -performance, scalable corporate applications.The above -mentioned examples show how to use Jakarta Ee API for common tasks such as Servlet development, database access, and message transmission.With the support of Jakarta EE, developers can build strong and reliable enterprise applications more efficiently.
