Notify the user when no LinkHandler supports a URI

Author: tferr

src/main/java/org/scijava/desktop/links/DefaultLinkService.java

@@ -29,6 +29,7 @@
 package org.scijava.desktop.links;
 
 import java.awt.Desktop;
+import java.awt.GraphicsEnvironment;
 import java.net.URI;
 import java.util.Arrays;
 import java.util.Collections;
@@ -46,6 +47,8 @@
 import org.scijava.plugin.Parameter;
 import org.scijava.plugin.Plugin;
 import org.scijava.service.Service;
+import org.scijava.ui.DialogPrompt;
+import org.scijava.ui.UIService;
 
 /**
  * Default implementation of {@link LinkService}.
@@ -61,6 +64,12 @@ public class DefaultLinkService extends AbstractHandlerService<URI, LinkHandler>
 	@Parameter(required = false)
 	private PlatformService platformService;
 
+	@Parameter(required = false)
+	private UIService uiService;
+
+	/** Maximum number of characters of an unsupported URI shown to the user. */
+	private static final int MAX_URI_DISPLAY_LENGTH = 120;
+
 	@EventHandler
 	private void onEvent(final ContextCreatedEvent evt) {
 		// Register URI handler with the desktop system, if possible.
@@ -75,6 +84,26 @@ private void onEvent(final ContextCreatedEvent evt) {
 		installSchemes();
 	}
 
+	@Override
+	public void handleUnsupported(final URI uri) {
+		final String appName = System.getProperty("scijava.app.name", "This application");
+		final String appDir = System.getProperty("scijava.app.directory");
+		String shown = String.valueOf(uri);
+		if (shown.length() > MAX_URI_DISPLAY_LENGTH) {
+			shown = shown.substring(0, MAX_URI_DISPLAY_LENGTH) + "...";
+		}
+		final String msg = appName + " cannot handle this link:\n\n" + shown +
+			"\n\nThe component that supports it may be missing or outdated. " +
+			"Please make sure it is installed and up to date." +
+			(appDir == null ? "" : "\n\nIf several installations exist in your system, " +
+				"the one that received this link may not include the component it " +
+				"needs. This link has been opened by:\n" + appDir);
+		if (log != null) log.warn(msg.replace("\n\n", " ").replace("\n", " "));
+		if (uiService != null && !GraphicsEnvironment.isHeadless()) {
+			uiService.showDialog(msg, "Unsupported Link", DialogPrompt.MessageType.ERROR_MESSAGE);
+		}
+	}
+
 	/**
 	 * Installs URI schemes with the operating system.
 	 * <p>

src/main/java/org/scijava/desktop/links/LinkService.java

@@ -54,14 +54,30 @@ default void handle(final URI uri) {
 			.findFirst();
 		if (match.isEmpty()) {
 			// No appropriate link handler plugin was found.
-			final Logger log = log();
-			if (log != null) log.debug("No handler for URI: " + uri);
+			handleUnsupported(uri);
 			return; // no handler for this URI
 		}
 		// Handle the URI using the matching link handler.
 		match.get().handle(uri);
 	}
 
+	/**
+	 * Called by {@link #handle(URI)} when no {@link LinkHandler} supports the
+	 * given URI. This typically happens when a link is opened by an installation
+	 * that lacks (or has an outdated version of) the component that implements
+	 * it, since the operating system routes links by scheme only.
+	 * <p>
+	 * The default implementation only logs a debug message. Implementations
+	 * with access to a user interface should override it to notify the user.
+	 * </p>
+	 *
+	 * @param uri The URI that no handler supports.
+	 */
+	default void handleUnsupported(final URI uri) {
+		final Logger log = log();
+		if (log != null) log.debug("No handler for URI: " + uri);
+	}
+
 	default Set<String> getSchemes() {
 		var schemes = new HashSet<String>();
 		for (final LinkHandler handler : getInstances()) {