feat: support DynamicTheme initialization in multi-version add-ons

README.md

@@ -64,6 +64,11 @@ public class AppShellConfiguratorImpl implements AppShellConfigurator {
 }
 ```
 
+When targeting Vaadin 14-25 or 23-25, the `AppShellConfigurator` approach cannot be used due to framework and library limitations.
+To resolve this, you must create a configuration file `src/test/resources/META-INF/dynamic-theme.properties` with the following content:
+```properties
+theme=LUMO
+```
 
 ## Code Viewer
 

src/main/java/com/flowingcode/vaadin/addons/demo/DynamicTheme.java

@@ -6,8 +6,10 @@
 import com.vaadin.flow.server.AppShellSettings;
 import com.vaadin.flow.server.VaadinSession;
 import com.vaadin.flow.server.Version;
+import com.vaadin.flow.server.communication.IndexHtmlResponse;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
+import org.jsoup.nodes.Element;
 
 /**
  * Enumeration representing supported themes for dynamic switching.
@@ -84,12 +86,12 @@ public static DynamicTheme getCurrent() {
   }
 
   /**
-   * Initializes the theme settings.
+   * Initializes the theme settings into the provided {@code AppShellSettings}.
    * <p>
-   * This method performs a lazy initialization of the {@link DynamicTheme} within the
+   * This method performs a lazy initialization of the {@code DynamicTheme} within the
    * current {@link VaadinSession}. If no theme is present, it registers this instance
    * as the session default. Subsequently, it injects the corresponding CSS stylesheet
-   * link into the {@link AppShellSettings}.
+   * link into the document head.
    * </p>
    *
    * @param settings the application shell settings to be modified
@@ -116,6 +118,47 @@ public void initialize(AppShellSettings settings) {
     }
   }
 
+  /**
+   * Initializes the theme settings into the provided {@code IndexHtmlResponse}.
+   * <p>
+   * This method performs a lazy initialization of the {@code DynamicTheme} within the
+   * current {@link VaadinSession}. If no theme is present, it registers this instance
+   * as the session default. Subsequently, it injects the corresponding CSS stylesheet
+   * link into the document head.
+   * </p>
+   *
+   * @param response the index HTML response to be modified
+   * @throws UnsupportedOperationException if the runtime Vaadin version is older than 25
+   */
+  public void initialize(IndexHtmlResponse response) {
+    assertFeatureSupported();
+
+    DynamicTheme theme = getCurrent();
+    if (theme == null) {
+      theme = this;
+      VaadinSession.getCurrent().setAttribute(DynamicTheme.class, theme);
+    }
+
+    String href = null;
+    switch (theme) {
+      case AURA:
+        href = "aura/aura.css";
+        break;
+      case LUMO:
+        href = "lumo/lumo.css";
+        break;
+      default:
+        break;
+    }
+
+    if (href != null) {
+      Element link = response.getDocument().createElement("link");
+      link.attr("rel", "stylesheet");
+      link.attr("href", href);
+      response.getDocument().head().appendChild(link);
+    }
+  }
+
   /**
    * Prepares the component for dynamic theme switching by preloading stylesheets.
    * <p>

src/main/java/com/flowingcode/vaadin/addons/demo/DynamicThemeInitializer.java

@@ -0,0 +1,41 @@
+package com.flowingcode.vaadin.addons.demo;
+
+import com.vaadin.flow.server.ServiceInitEvent;
+import com.vaadin.flow.server.VaadinServiceInitListener;
+import com.vaadin.flow.server.communication.IndexHtmlRequestListener;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Properties;
+
+/**
+ * Service initialization listener that automatically applies a dynamic theme.
+ * <p>
+ * If the dynamic theme feature is supported, this listener checks for the presence of a
+ * {@code /META-INF/dynamic-theme.properties} file. If found, it reads the {@code theme} property
+ * (e.g., {@code theme=LUMO}) and registers an {@link IndexHtmlRequestListener} to initialize the
+ * theme for all requests.
+ * </p>
+ */
+@SuppressWarnings("serial")
+public class DynamicThemeInitializer implements VaadinServiceInitListener {
+
+  @Override
+  public void serviceInit(ServiceInitEvent event) {
+    if (DynamicTheme.isFeatureSupported()) {
+      try (InputStream in = getClass().getResourceAsStream("/META-INF/dynamic-theme.properties")) {
+        if (in != null) {
+          Properties props = new Properties();
+          props.load(in);
+          String themeName = props.getProperty("theme");
+          if (themeName != null) {
+            DynamicTheme theme = DynamicTheme.valueOf(themeName.trim());
+            event.addIndexHtmlRequestListener(theme::initialize);
+          }
+        }
+      } catch (IOException e) {
+        throw new RuntimeException("Error reading dynamic-theme.properties", e);
+      }
+    }
+  }
+
+}

src/main/resources/META-INF/services/com.vaadin.flow.server.VaadinServiceInitListener

@@ -1 +1,2 @@
-com.flowingcode.vaadin.addons.DevSourceRequestHandlerInitializer
+com.flowingcode.vaadin.addons.DevSourceRequestHandlerInitializer
+com.flowingcode.vaadin.addons.demo.DynamicThemeInitializer