Move file-type-related logic to separate service

This commit introduces a new DesktopService, more general than
LinkService. While the LinkService is focused on handling URI schemes
in an extensible way, the DesktopService provides a way to manage the
application's supported file extensions and associated MIME types.

Author: ctrueden

src/main/java/org/scijava/desktop/DefaultDesktopService.java

@@ -0,0 +1,71 @@
+/*-
+ * #%L
+ * Desktop integration for SciJava.
+ * %%
+ * Copyright (C) 2010 - 2026 SciJava developers.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+package org.scijava.desktop;
+
+import org.scijava.plugin.Plugin;
+import org.scijava.service.AbstractService;
+import org.scijava.service.SciJavaService;
+import org.scijava.service.Service;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Service interface for an application's desktop-related concerns.
+ *
+ * @author Curtis Rueden
+ */
+@Plugin(type = Service.class)
+public class DefaultDesktopService extends AbstractService implements DesktopService {
+
+	private final Map<String, String> fileTypes = new HashMap<>();
+
+	@Override
+	public void addFileType(String ext, String mimeType) {
+		fileTypes.put(ext, mimeType);
+	}
+
+	@Override
+	public void addFileTypes(String mimePrefix, String... extensions) {
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+
+	@Override
+	public void addFileTypes(final Map<String, String> extToMimeType) {
+		fileTypes.putAll(extToMimeType);
+	}
+
+	/**
+	 * Gets the map of supported file types.
+	 */
+	public Map<String, String> getFileTypes() {
+		return Collections.unmodifiableMap(fileTypes);
+	}
+}

src/main/java/org/scijava/desktop/DesktopService.java

@@ -0,0 +1,79 @@
+/*-
+ * #%L
+ * Desktop integration for SciJava.
+ * %%
+ * Copyright (C) 2010 - 2026 SciJava developers.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+package org.scijava.desktop;
+
+import org.scijava.desktop.links.LinkHandler;
+import org.scijava.service.SciJavaService;
+
+import java.util.Map;
+
+/**
+ * Service interface for an application's desktop-related concerns.
+ *
+ * @author Curtis Rueden
+ */
+public interface DesktopService extends SciJavaService {
+
+	/**
+	 * Adds to the set of supported file types, looking up each extension's MIME
+	 * type from the built-in database. If an extension is not found in the
+	 * database, it falls back to {@code mimePrefix/x-ext} (e.g. passing prefix
+	 * {@code "image"} for unknown extension {@code "foo"} yields
+	 * {@code "image/x-foo"}).
+	 *
+	 * @param mimePrefix The MIME type prefix (e.g. {@code "image"},
+	 *                   {@code "application"}) used when an extension is absent
+	 *                   from the database.
+	 * @param extensions One or more file extensions to register (without leading
+	 *                   dot, e.g. {@code "tiff"}, {@code "png"}).
+	 */
+	void addFileTypes(String mimePrefix, String... extensions);
+
+	/**
+	 * Adds to the set of supported file types using an explicit mapping.
+	 *
+	 * @param extToMimeType Map from file extension (without leading dot,
+	 *                      e.g. {@code "png"}) to MIME type
+	 *                      (e.g. {@code "image/png"}).
+	 */
+	void addFileTypes(Map<String, String> extToMimeType);
+
+	/**
+	 * Adds a single file type with an explicit MIME type.
+	 *
+	 * @param ext      File extension without leading dot (e.g. {@code "png"}).
+	 * @param mimeType MIME type (e.g. {@code "image/png"}).
+	 */
+	void addFileType(String ext, String mimeType);
+
+	/**
+	 * Gets the map of supported file types.
+	 */
+	Map<String, String> getFileTypes();
+}

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

@@ -36,6 +36,7 @@
 import java.util.Set;
 
 import org.scijava.desktop.DesktopIntegrationProvider;
+import org.scijava.desktop.DesktopService;
 import org.scijava.event.ContextCreatedEvent;
 import org.scijava.event.EventHandler;
 import org.scijava.log.LogService;
@@ -60,25 +61,6 @@ public class DefaultLinkService extends AbstractHandlerService<URI, LinkHandler>
 	@Parameter(required = false)
 	private PlatformService platformService;
 
-	private final Set<String> extensions = new HashSet<>();
-
-	/**
-	 * Gets supported file extensions.
-	 */
-	@Override
-	public Set<String> getFileExtensions() {
-		return Collections.unmodifiableSet(extensions);
-	}
-
-	/**
-	 * Gets supported file extensions.
-	 */
-	@Override
-	public void addFileExtensions(final String... extensions) {
-		this.extensions.addAll(Arrays.asList(extensions));
-	}
-
-
 	@EventHandler
 	private void onEvent(final ContextCreatedEvent evt) {
 		// Register URI handler with the desktop system, if possible.

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

@@ -47,22 +47,12 @@ public interface LinkService extends HandlerService<URI, LinkHandler>,
 	SciJavaService
 {
 
-	/**
-	 * Gets the set of supported file extensions.
-	 */
-	public Set<String> getFileExtensions();
-
-	/**
-	 * Adds to the set of supported file extensions.
-	 */
-	public void addFileExtensions(final String... extension);
-
 	default void handle(final URI uri) {
 		// Find the highest-priority link handler plugin which matches, if any.
 		final Optional<LinkHandler> match = getInstances().stream() //
 			.filter(handler -> handler.supports(uri)) //
 			.findFirst();
-		if (!match.isPresent()) {
+		if (match.isEmpty()) {
 			// No appropriate link handler plugin was found.
 			final Logger log = log();
 			if (log != null) log.debug("No handler for URI: " + uri);

src/main/java/org/scijava/desktop/platform/linux/LinuxPlatform.java

@@ -32,6 +32,7 @@
 import org.scijava.Context;
 import org.scijava.app.AppService;
 import org.scijava.desktop.DesktopIntegrationProvider;
+import org.scijava.desktop.DesktopService;
 import org.scijava.desktop.links.LinkService;
 import org.scijava.desktop.links.SchemeInstaller;
 import org.scijava.log.LogService;
@@ -400,10 +401,14 @@ private Set<String> schemes() {
 			Collections.emptySet() : linkService.getSchemes();
 	}
 
-	private Set<String> extensions() {
-		final LinkService linkService = linkService();
-		return linkService == null ?
-			Collections.emptySet() : linkService.getFileExtensions();
+	private DesktopService desktopService() {
+		return context.getService(DesktopService.class);
+	}
+
+	private Map<String, String> fileTypes() {
+		final DesktopService desktopService = desktopService();
+		return desktopService == null ?
+			Collections.emptyMap() : desktopService.getFileTypes();
 	}
 
 	/**
@@ -414,7 +419,7 @@ private synchronized Map<String, String> loadMimeTypeMapping() throws IOExceptio
 
 		extensionToMime = new LinkedHashMap<>();
 
-		final Set<String> extensions = extensions();
+		final Map<String, String> fileTypes = fileTypes();
 		// TODO: How do we know the MIME type of each extension?
 
 		return extensionToMime;

src/main/java/org/scijava/desktop/platform/windows/WindowsPlatform.java

@@ -36,6 +36,7 @@
 
 import org.scijava.Context;
 import org.scijava.desktop.DesktopIntegrationProvider;
+import org.scijava.desktop.DesktopService;
 import org.scijava.desktop.links.LinkService;
 import org.scijava.desktop.links.SchemeInstaller;
 import org.scijava.log.LogService;
@@ -267,10 +268,14 @@ private Set<String> schemes() {
 			Collections.emptySet() : linkService.getSchemes();
 	}
 
+	private DesktopService desktopService() {
+		return context.getService(DesktopService.class);
+	}
+
 	private Set<String> extensions() {
-		final LinkService linkService = linkService();
-		return linkService == null ?
-			Collections.emptySet() : linkService.getFileExtensions();
+		final DesktopService desktopService = desktopService();
+		return desktopService == null ?
+			Collections.emptySet() : desktopService.getFileTypes().keySet();
 	}
 
 	/**