Add Server-Side Page Fragment Composition pattern #2697

- Implement complete Server-Side Page Fragment Composition design pattern
- Add microservices for header, content, and footer fragments
- Create composition service for server-side page assembly
- Include comprehensive documentation and examples
- Add unit tests with 17 test cases covering all functionality
- Support both synchronous and asynchronous composition
- Include caching, personalization, and performance monitoring
- Follow project contribution guidelines and coding standards

Closes #2697

Author: athikha

server-side-fragment-composition/src/main/java/com/iluwatar/serverfragment/App.java

@@ -33,169 +33,169 @@
 
 /**
  * Server-Side Page Fragment Composition pattern demonstration.
- * 
- * <p>This pattern demonstrates how to compose web pages from fragments 
- * delivered by different microservices. Each fragment is managed independently,
- * allowing for modular development, deployment, and scaling.
- * 
+ *
+ * <p>This pattern demonstrates how to compose web pages from fragments delivered by different
+ * microservices. Each fragment is managed independently, allowing for modular development,
+ * deployment, and scaling.
+ *
  * <p>The key elements of this pattern include:
+ *
  * <ul>
- *   <li><strong>Fragment Composition:</strong> Server assembles webpage from various fragments</li>
- *   <li><strong>Microservices:</strong> Each fragment managed by separate microservice</li>
- *   <li><strong>Scalability:</strong> Independent development, deployment, and scaling</li>
- *   <li><strong>Performance:</strong> Server-side assembly optimizes client performance</li>
- *   <li><strong>Consistent UX:</strong> Ensures cohesive user experience across fragments</li>
+ *   <li><strong>Fragment Composition:</strong> Server assembles webpage from various fragments
+ *   <li><strong>Microservices:</strong> Each fragment managed by separate microservice
+ *   <li><strong>Scalability:</strong> Independent development, deployment, and scaling
+ *   <li><strong>Performance:</strong> Server-side assembly optimizes client performance
+ *   <li><strong>Consistent UX:</strong> Ensures cohesive user experience across fragments
  * </ul>
- * 
+ *
  * <p>In this demo, we simulate three microservices:
+ *
  * <ul>
- *   <li><strong>HeaderService:</strong> Manages navigation and branding</li>
- *   <li><strong>ContentService:</strong> Manages main page content and personalization</li>
- *   <li><strong>FooterService:</strong> Manages footer content and promotional information</li>
+ *   <li><strong>HeaderService:</strong> Manages navigation and branding
+ *   <li><strong>ContentService:</strong> Manages main page content and personalization
+ *   <li><strong>FooterService:</strong> Manages footer content and promotional information
  * </ul>
  */
 @Slf4j
 public class App {
 
   /**
    * Main method demonstrating Server-Side Page Fragment Composition.
-   * 
-   * <p>This demonstration shows how multiple microservices can be coordinated
-   * to generate complete web pages, emphasizing the independence and scalability
-   * of each service while maintaining a cohesive user experience.
-   * 
+   *
+   * <p>This demonstration shows how multiple microservices can be coordinated to generate complete
+   * web pages, emphasizing the independence and scalability of each service while maintaining a
+   * cohesive user experience.
+   *
    * @param args command line arguments (not used in this demo)
    */
   public static void main(String[] args) {
     LOGGER.info("=== Starting Server-Side Page Fragment Composition Demo ===");
-    
+
     try {
       // Initialize and demonstrate the pattern
       var demo = new App();
       demo.runDemo();
-      
+
       LOGGER.info("=== Server-Side Page Fragment Composition Demo Completed Successfully ===");
-      
+
     } catch (Exception e) {
       LOGGER.error("Demo execution failed", e);
       System.exit(1);
     }
   }
 
-  /**
-   * Runs the complete demonstration of the Server-Side Page Fragment Composition pattern.
-   */
+  /** Runs the complete demonstration of the Server-Side Page Fragment Composition pattern. */
   private void runDemo() {
     LOGGER.info("Initializing microservices...");
-    
+
     // Create microservice instances
     // In a real system, these would be separate deployable services
     var headerService = new HeaderService();
     var contentService = new ContentService();
     var footerService = new FooterService();
-    
+
     LOGGER.info("Microservices initialized:");
     LOGGER.info("  - {}", headerService.getServiceInfo());
     LOGGER.info("  - {}", contentService.getServiceInfo());
     LOGGER.info("  - {}", footerService.getServiceInfo());
-    
+
     // Create and configure composition service
     LOGGER.info("Setting up composition service...");
     var compositionService = new CompositionService();
-    
+
     // Register microservices with the composition service
     compositionService.registerService("header", headerService);
     compositionService.registerService("content", contentService);
     compositionService.registerService("footer", footerService);
-    
+
     // Check health status
     LOGGER.info("Health Status: {}", compositionService.getHealthStatus());
-    
+
     // Demonstrate synchronous page composition for different page types
     demonstrateSynchronousComposition(compositionService);
-    
+
     // Demonstrate asynchronous page composition
     demonstrateAsynchronousComposition(compositionService);
-    
+
     // Demonstrate error handling
     demonstrateErrorHandling();
   }
 
-  /**
-   * Demonstrates synchronous page composition for various page types.
-   */
+  /** Demonstrates synchronous page composition for various page types. */
   private void demonstrateSynchronousComposition(CompositionService compositionService) {
     LOGGER.info("\n--- Demonstrating Synchronous Page Composition ---");
-    
-    var pageTypes = new String[]{"home", "about", "contact", "products"};
-    
+
+    var pageTypes = new String[] {"home", "about", "contact", "products"};
+
     for (var pageType : pageTypes) {
       LOGGER.info("Composing '{}' page...", pageType);
-      
+
       var startTime = System.currentTimeMillis();
       var completePage = compositionService.composePage(pageType);
       var compositionTime = System.currentTimeMillis() - startTime;
-      
-      LOGGER.info("'{}' page composed in {}ms (size: {} characters)", 
-          pageType, compositionTime, completePage.length());
-      
+
+      LOGGER.info(
+          "'{}' page composed in {}ms (size: {} characters)",
+          pageType,
+          compositionTime,
+          completePage.length());
+
       // Log a sample of the composed page for verification
       var preview = getPagePreview(completePage);
       LOGGER.debug("Page preview for '{}': {}", pageType, preview);
     }
   }
 
-  /**
-   * Demonstrates asynchronous page composition for improved performance.
-   */
+  /** Demonstrates asynchronous page composition for improved performance. */
   private void demonstrateAsynchronousComposition(CompositionService compositionService) {
     LOGGER.info("\n--- Demonstrating Asynchronous Page Composition ---");
-    
+
     var pageType = "home";
     LOGGER.info("Composing '{}' page asynchronously...", pageType);
-    
+
     var startTime = System.currentTimeMillis();
-    
+
     try {
       var futureResult = compositionService.composePageAsync(pageType);
       var completePage = futureResult.get(); // Wait for completion
       var compositionTime = System.currentTimeMillis() - startTime;
-      
-      LOGGER.info("Async '{}' page composed in {}ms (size: {} characters)", 
-          pageType, compositionTime, completePage.length());
-      
+
+      LOGGER.info(
+          "Async '{}' page composed in {}ms (size: {} characters)",
+          pageType,
+          compositionTime,
+          completePage.length());
+
       var preview = getPagePreview(completePage);
       LOGGER.debug("Async page preview: {}", preview);
-      
+
     } catch (Exception e) {
       LOGGER.error("Async composition failed for page: {}", pageType, e);
     }
   }
 
-  /**
-   * Demonstrates error handling in the composition process.
-   */
+  /** Demonstrates error handling in the composition process. */
   private void demonstrateErrorHandling() {
     LOGGER.info("\n--- Demonstrating Error Handling ---");
-    
+
     // Create a new composition service without registered services
     var emptyCompositionService = new CompositionService();
-    
+
     try {
       LOGGER.info("Attempting to compose page without registered services...");
       emptyCompositionService.composePage("test");
-      
+
     } catch (IllegalStateException e) {
       LOGGER.info("Expected error caught: {}", e.getMessage());
       LOGGER.info("Error handling working correctly - services must be registered");
     }
-    
+
     // Demonstrate invalid service registration
     var validCompositionService = new CompositionService();
     try {
       LOGGER.info("Attempting to register invalid service type...");
       validCompositionService.registerService("invalid", new Object());
-      
+
     } catch (IllegalArgumentException e) {
       LOGGER.info("Expected error caught: {}", e.getMessage());
       LOGGER.info("Error handling working correctly - only valid service types accepted");
@@ -212,16 +212,16 @@ private String getPagePreview(String completePage) {
     if (completePage == null || completePage.length() < 100) {
       return completePage;
     }
-    
+
     // Extract title and first bit of content for preview
     var titleStart = completePage.indexOf("<title>");
     var titleEnd = completePage.indexOf("</title>");
-    
+
     if (titleStart != -1 && titleEnd != -1) {
       var title = completePage.substring(titleStart + 7, titleEnd);
       return String.format("Title: '%s', Length: %d chars", title, completePage.length());
     }
-    
+
     return String.format("HTML page, Length: %d chars", completePage.length());
   }
-}
+}