import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PARAMETER)
public @interface NotEmpty {
}

public class UserService {
    public void register(@NotEmpty String username) {
        System.out.println("Registering user: " + username);
    }
}

import java.lang.reflect.*;

public class Validator {

    public static void main(String[] args) throws Exception {
        UserService service = new UserService();
        Method method = service.getClass().getMethod("register", String.class);

        Object[] params = {""};  // ورودی تستی

        Annotation[][] annotations = method.getParameterAnnotations();
        for (int i = 0; i < annotations.length; i++) {
            for (Annotation a : annotations[i]) {
                if (a instanceof NotEmpty &&
                    params[i] instanceof String &&
                    ((String) params[i]).isEmpty()) {
                    throw new IllegalArgumentException("The parameter must not be empty!");
                }
            }
        }

        method.invoke(service, params);  // اجرای متد در صورت اعتبارسنجی موفق
    }
}

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface LogExecution {
}

public class OrderService {
    @LogExecution
    public void placeOrder() {
        System.out.println("The order was placed.");
    }
}

import java.lang.reflect.*;

public class Logger {

    public static void main(String[] args) throws Exception {
        OrderService service = new OrderService();
        Method method = service.getClass().getMethod("placeOrder");

        if (method.isAnnotationPresent(LogExecution.class)) {
            System.out.println("Start method execution: " + method.getName());
            method.invoke(service);
            System.out.println("End of method execution: " + method.getName());
        }
    }
}

Start method execution: placeOrder  
The order was placed.  
End of method execution: placeOrder

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#کاربرـحرفهـای

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import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class HelloServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<h1>سلام از Servlet!</h1>");
    }
}

@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
    // همان کد بالا
}

#کاربرـحرفهـای

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import jakarta.persistence.*;

@Entity
public class User {

    @Id
    @GeneratedValue
    private Long id;

    private String name;

    private String email;

    // getters & setters
}

EntityManagerFactory emf = Persistence.createEntityManagerFactory("my-unit");
EntityManager em = emf.createEntityManager();

User user = new User();
user.setName("Saleh");
user.setEmail("[email protected]");

em.getTransaction().begin();
em.persist(user);
em.getTransaction().commit();

em.close();
emf.close();

<persistence xmlns="http://jakarta.ee/xml/ns/persistence" version="3.0">
  <persistence-unit name="my-unit">
    <class>User</class>
    <properties>
      <property name="jakarta.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/testdb"/>
      <property name="jakarta.persistence.jdbc.user" value="root"/>
      <property name="jakarta.persistence.jdbc.password" value="1234"/>
      <property name="jakarta.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
      <property name="jakarta.persistence.schema-generation.database.action" value="create"/>
    </properties>
  </persistence-unit>
</persistence>

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public class MessageService {
    public void send(String msg) {
        System.out.println("Sending message: " + msg);
    }
}

import jakarta.inject.Inject;

public class NotificationManager {

    @Inject
    private MessageService messageService;

    public void notifyUser() {
        messageService.send("کاربر گرامی، خوش آمدید!");
    }
}

<!-- WEB-INF/beans.xml -->
<beans xmlns="https://jakarta.ee/xml/ns/jakartaee" version="4.0" />

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