Add CustomerService with virtual threads and update test classes

Introduced CustomerService using virtual threads for efficient customer data fetching. Renamed existing test and main classes to reflect their use of virtual threads. Added comprehensive test for CustomerService to validate functionality and performance.

src/main/java/com/kousenit/virtualthreads/CustomerService.java

@@ -0,0 +1,46 @@
+package com.kousenit.virtualthreads;
+
+import java.util.List;
+import java.util.concurrent.*;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+public class CustomerService {
+
+    public List<Customer> fetchCustomerData(List<Integer> customerIds) {
+        try (ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor()) {
+            List<CompletableFuture<Customer>> futures = customerIds.stream()
+                    .map(id -> CompletableFuture.supplyAsync(() -> fetchCustomer(id), executor))
+                    .toList();
+
+            return CompletableFuture.allOf(futures.toArray(CompletableFuture[]::new))
+                    .thenApply(v -> futures.stream()
+                            .map(CompletableFuture::join)
+                            .toList())
+                    .join();
+        }
+    }
+
+    private Customer fetchCustomer(int id) {
+        try {
+            // Simulate API call or database query
+            Thread.sleep(1000);
+            return new Customer(id, "Customer " + id, "customer" + id + "@example.com");
+        } catch (InterruptedException e) {
+            throw new RuntimeException("Thread interrupted while fetching customer " + id, e);
+        }
+    }
+
+    // Customer as a record
+    public record Customer(int id, String name, String email) {}
+
+    // Main method for demonstration
+    public static void main(String[] args) {
+        CustomerService service = new CustomerService();
+        List<Integer> customerIds = IntStream.rangeClosed(1, 5)
+                .boxed()
+                .collect(Collectors.toList());
+        List<Customer> customers = service.fetchCustomerData(customerIds);
+        customers.forEach(System.out::println);
+    }
+}

src/main/java/com/kousenit/virtualthreads/Demo.java → src/main/java/com/kousenit/virtualthreads/VirtualThreadsDemo.java

@@ -5,7 +5,7 @@
 import java.util.stream.IntStream;
 
 // Example from: https://openjdk.org/jeps/444 (Virtual Threads)
-public class Demo {
+public class VirtualThreadsDemo {
     public static void main(String[] args) {
         long startTime = System.nanoTime();
         try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {

src/test/java/com/kousenit/generics/SafeVaragsDemoTest.java → src/test/java/com/kousenit/generics/SafeVaragsVirtualThreadsDemoTest.java

@@ -9,7 +9,7 @@
 import static org.hamcrest.Matchers.arrayContaining;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
-class SafeVaragsDemoTest {
+class SafeVaragsVirtualThreadsDemoTest {
     private final SafeVaragsDemo demo = new SafeVaragsDemo();
     private final LocalDate now = LocalDate.now();
 

src/test/java/com/kousenit/interfaces/PrivateDemoTest.java → src/test/java/com/kousenit/interfaces/PrivateVirtualThreadsDemoTest.java

@@ -4,7 +4,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-public class PrivateDemoTest {
+public class PrivateVirtualThreadsDemoTest {
     private final PrivateDemo demo = new PrivateDemo();
 
     @Test

src/test/java/com/kousenit/virtualthreads/CustomerServiceTest.java

@@ -0,0 +1,46 @@
+package com.kousenit.virtualthreads;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.stream.IntStream;
+
+import static com.kousenit.virtualthreads.CustomerService.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class CustomerServiceTest {
+
+    @Test
+    void testFetchCustomerData() {
+        CustomerService service = new CustomerService();
+        List<Integer> customerIds = IntStream.rangeClosed(1, 500)
+                .boxed()
+                .toList();
+
+        long startTime = System.currentTimeMillis();
+        var customers = service.fetchCustomerData(customerIds);
+        long endTime = System.currentTimeMillis();
+
+        // Check if we got the correct number of customers
+        assertEquals(500, customers.size(), "Should fetch 500 customers");
+
+        // Verify first and last customer data
+        Customer firstCustomer = customers.getFirst();
+        Customer lastCustomer = customers.getLast();
+
+        assertEquals(1, firstCustomer.id(), "First customer ID should be 1");
+        assertEquals("Customer 1", firstCustomer.name(), "First customer name should match");
+        assertEquals("[email protected]", firstCustomer.email(), "First customer email should match");
+
+        assertEquals(500, lastCustomer.id(), "Last customer ID should be 500");
+        assertEquals("Customer 500", lastCustomer.name(), "Last customer name should match");
+        assertEquals("[email protected]", lastCustomer.email(), "Last customer email should match");
+
+        // Check if the execution time is close to 1 second (allowing some margin)
+        long executionTime = endTime - startTime;
+        assertTrue(executionTime >= 1000 && executionTime < 1500,
+                "Execution time should be close to 1 second, but was " + executionTime + " ms");
+        System.out.println("Execution time: " + executionTime + " ms");
+    }
+}