[DEMO] Add an E4 RCP example that swaps icons through IImageURLModifier

bundles/org.eclipse.e4.ui.workbench.swt/META-INF/MANIFEST.MF

@@ -9,7 +9,7 @@ Bundle-Activator: org.eclipse.e4.ui.internal.workbench.swt.WorkbenchSWTActivator
 Require-Bundle: org.eclipse.e4.ui.workbench;bundle-version="0.10.0",
  org.eclipse.e4.core.services;bundle-version="1.0.0",
  org.eclipse.e4.ui.services;bundle-version="0.1.0",
- org.eclipse.jface;bundle-version="[3.39.0,4.0.0)",
+ org.eclipse.jface;bundle-version="[3.41.0,4.0.0)",
  org.eclipse.e4.ui.dialogs;bundle-version="1.1.600",
  org.eclipse.core.databinding;bundle-version="[1.2.0,2.0.0)",
  org.eclipse.jface.databinding;bundle-version="[1.3.0,2.0.0)",

bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/ImageURLModifierTracker.java

@@ -0,0 +1,64 @@
+/*******************************************************************************
+ * Copyright (c) 2026 vogella GmbH and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Lars Vogel <Lars.Vogel@vogella.com> - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.e4.ui.internal.workbench.swt;
+
+import org.eclipse.jface.resource.IImageURLModifier;
+import org.eclipse.jface.resource.ImageDescriptor;
+import org.osgi.framework.BundleContext;
+import org.osgi.framework.ServiceReference;
+import org.osgi.util.tracker.ServiceTracker;
+
+/**
+ * Installs the highest ranked {@link IImageURLModifier} service in JFace.
+ * Tracked because the contributing bundle may start after the workbench.
+ */
+class ImageURLModifierTracker extends ServiceTracker<IImageURLModifier, IImageURLModifier> {
+
+	private ServiceReference<IImageURLModifier> installed;
+
+	ImageURLModifierTracker(BundleContext context) {
+		super(context, IImageURLModifier.class, null);
+	}
+
+	@Override
+	public synchronized IImageURLModifier addingService(ServiceReference<IImageURLModifier> reference) {
+		IImageURLModifier modifier = super.addingService(reference);
+		// not tracked until this returns, so it cannot be picked by installBest()
+		if (modifier != null && (installed == null || reference.compareTo(installed) > 0)) {
+			installed = reference;
+			ImageDescriptor.setURLModifier(modifier);
+		}
+		return modifier;
+	}
+
+	@Override
+	public synchronized void modifiedService(ServiceReference<IImageURLModifier> reference,
+			IImageURLModifier service) {
+		installBest();
+	}
+
+	@Override
+	public synchronized void removedService(ServiceReference<IImageURLModifier> reference,
+			IImageURLModifier service) {
+		super.removedService(reference, service);
+		if (reference.equals(installed)) {
+			installBest();
+		}
+	}
+
+	private void installBest() {
+		installed = getServiceReference();
+		ImageDescriptor.setURLModifier(installed == null ? null : getService(installed));
+	}
+}

bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/WorkbenchSWTActivator.java

@@ -43,6 +43,7 @@
 import org.eclipse.core.runtime.Platform;
 import org.eclipse.jface.dialogs.DialogSettings;
 import org.eclipse.jface.dialogs.IDialogSettings;
+import org.eclipse.jface.resource.IImageURLModifier;
 import org.eclipse.osgi.service.datalocation.Location;
 import org.eclipse.osgi.service.debug.DebugOptions;
 import org.eclipse.osgi.service.debug.DebugOptionsListener;
@@ -62,6 +63,7 @@ public class WorkbenchSWTActivator implements BundleActivator, DebugOptionsListe
 
 	private BundleContext context;
 	private ServiceTracker<?, Location> locationTracker;
+	private ServiceTracker<IImageURLModifier, IImageURLModifier> imageURLModifierTracker;
 	private static WorkbenchSWTActivator activator;
 	private DebugTrace trace;
 
@@ -89,11 +91,17 @@ public void start(BundleContext context) throws Exception {
 		Hashtable<String, String> props = new Hashtable<>(2);
 		props.put(DebugOptions.LISTENER_SYMBOLICNAME, PI_RENDERERS);
 		context.registerService(DebugOptionsListener.class, this, props);
+		imageURLModifierTracker = new ImageURLModifierTracker(context);
+		imageURLModifierTracker.open();
 	}
 
 	@Override
 	public void stop(BundleContext context) throws Exception {
 		saveDialogSettings();
+		if (imageURLModifierTracker != null) {
+			imageURLModifierTracker.close();
+			imageURLModifierTracker = null;
+		}
 	}
 
 	public Bundle getBundle() {

bundles/org.eclipse.jface/src/org/eclipse/jface/resource/IImageURLModifier.java

@@ -0,0 +1,41 @@
+/*******************************************************************************
+ * Copyright (c) 2026 vogella GmbH and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Lars Vogel <Lars.Vogel@vogella.com> - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.jface.resource;
+
+import java.net.URL;
+
+/**
+ * Rewrites image URLs before they are loaded, so icons can be substituted
+ * without changing the code that creates the image descriptors. The E4
+ * workbench installs the highest ranked OSGi service of this type.
+ * <p>
+ * <strong>EXPERIMENTAL</strong>. This interface has been added as part of a
+ * work in progress. There is no guarantee that this API will remain the same.
+ * </p>
+ *
+ * @see ImageDescriptor#setURLModifier(IImageURLModifier)
+ * @since 3.41
+ */
+@FunctionalInterface
+public interface IImageURLModifier {
+
+	/**
+	 * Returns the URL to load instead of the given one, or <code>null</code> to
+	 * keep it. Called for every image load, so it must be fast and thread-safe.
+	 *
+	 * @param originalURL the URL the image would be loaded from
+	 * @return the replacement URL, or <code>null</code> to keep the original
+	 */
+	URL modifyURL(URL originalURL);
+}

bundles/org.eclipse.jface/src/org/eclipse/jface/resource/ImageDescriptor.java

@@ -82,6 +82,24 @@ protected ImageDescriptor() {
 		super(shouldBeCached);
 	}
 
+	/** Set from OSGi service events, read from any thread. */
+	static volatile IImageURLModifier urlModifier;
+
+	/**
+	 * Installs the modifier consulted when an image is loaded from a URL. Images
+	 * created before are not reloaded.
+	 * <p>
+	 * <strong>EXPERIMENTAL</strong>. This method has been added as part of a work
+	 * in progress. There is no guarantee that this API will remain the same.
+	 * </p>
+	 *
+	 * @param modifier the modifier, or <code>null</code> to remove it
+	 * @since 3.41
+	 */
+	public static void setURLModifier(IImageURLModifier modifier) {
+		urlModifier = modifier;
+	}
+
 	private static final ImageDescriptor NULL_IMAGE = createFromImageDataProvider(z -> null);
 
 	/**

bundles/org.eclipse.jface/src/org/eclipse/jface/resource/URLImageDescriptor.java

@@ -63,7 +63,7 @@ private ImageFileNameProvider createURLImageFileNameProvider() {
 					// The calling image will do that itself!
 					return getFilePath(tempURL, logIOException);
 				}
-				return getZoomedImageSource(tempURL, url, zoom, u -> getFilePath(u, logIOException));
+				return getZoomedImageSource(tempURL, zoom, u -> getFilePath(u, logIOException));
 			}
 			return null;
 		};
@@ -107,22 +107,23 @@ public ImageData getImageData(int zoom) {
 			if (zoom == 100 || canLoadAtZoom(tempURL, zoom)) {
 				return getImageData(tempURL, 100, zoom);
 			}
-			return getZoomedImageSource(tempURL, url, zoom, u -> getImageData(u, zoom, zoom));
+			return getZoomedImageSource(tempURL, zoom, u -> getImageData(u, zoom, zoom));
 		}
 		return null;
 	}
 
-	private static <R> R getZoomedImageSource(URL url, String urlString, int zoom, Function<URL, R> getImage) {
+	private static <R> R getZoomedImageSource(URL url, int zoom, Function<URL, R> getImage) {
 		URL xUrl = getxURL(url, zoom);
 		if (xUrl != null) {
 			R xdata = getImage.apply(xUrl);
 			if (xdata != null) {
 				return xdata;
 			}
 		}
-		String xpath = getxPath(urlString, zoom);
+		// derived from the already modified URL, so the modifier must not run again
+		String xpath = getxPath(url.toExternalForm(), zoom);
 		if (xpath != null) {
-			URL xPathUrl = getURL(xpath);
+			URL xPathUrl = toURL(xpath);
 			if (xPathUrl != null) {
 				return getImage.apply(xPathUrl);
 			}
@@ -352,14 +353,30 @@ public Image createImage(boolean returnMissingImageOnError, Device device) {
 		}
 	}
 
+	/**
+	 * Resolves the given URL string, applying the URL modifier. Every code path of
+	 * this descriptor resolves its URL here.
+	 */
 	private static URL getURL(String urlString) {
-		URL result = null;
+		URL result = toURL(urlString);
+		IImageURLModifier modifier = urlModifier;
+		if (result != null && modifier != null) {
+			URL modified = modifier.modifyURL(result);
+			if (modified != null) {
+				result = modified;
+			}
+		}
+		return result;
+	}
+
+	@SuppressWarnings("deprecation") // keeps the lenient parsing of new URL(String)
+	private static URL toURL(String urlString) {
 		try {
-			result = new URL(urlString);
+			return new URL(urlString);
 		} catch (MalformedURLException e) {
 			Policy.logException(e);
+			return null;
 		}
-		return result;
 	}
 
 	@Override

examples/org.eclipse.ui.examples.urlmodifier/.classpath

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-17"/>
+	<classpathentry kind="con" path="org.eclipse.pde.core.requiredPlugins"/>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

examples/org.eclipse.ui.examples.urlmodifier/.project

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>org.eclipse.ui.examples.urlmodifier</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.pde.ManifestBuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.pde.SchemaBuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.pde.ds.core.builder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.pde.PluginNature</nature>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

examples/org.eclipse.ui.examples.urlmodifier/.settings/org.eclipse.core.resources.prefs

@@ -0,0 +1,2 @@
+eclipse.preferences.version=1
+encoding/<project>=UTF-8