[JEP-216] Add SPI for localized resource lookup

core/src/main/java/org/kohsuke/stapler/LocaleDrivenResourceProvider.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2019 Daniel Beck
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted provided
+ * that the following conditions are met:
+ *
+ *     * Redistributions of source code must retain the above copyright notice, this list of
+ *       conditions and the following disclaimer.
+ *     * 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 OWNER 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.
+ */
+
+package org.kohsuke.stapler;
+
+import javax.annotation.CheckForNull;
+import javax.annotation.Nonnull;
+import java.net.URL;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.ServiceLoader;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Service provider interface allowing to hook into webapp resource lookup.
+ *
+ * This cannot be made a property of WebApp as other behavior customizations, as webapp resource lookup is done before we have StaplerRequest/StaplerResponse.
+ */
+public abstract class LocaleDrivenResourceProvider {
+    /**
+     * Returns the URL corresponding to the specified resource path.
+     *
+     * The path can take two forms:
+     *
+     * <ul>
+     *     <li>A full URL represented as string. In Jenkins this is typically plugin webapp resources.</li>
+     *     <li>A path with leading slash. These are actual webapp resources, with that being the implicit base directory.</li>
+     * </ul>
+     *
+     * @param path the path to the resource
+     * @return the URL to the file, if it is to be overridden, null otherwise.
+     */
+    @CheckForNull
+    abstract public URL lookup(@Nonnull String path);
+
+    private static List<LocaleDrivenResourceProvider> localeDrivenResourceProviders;
+
+    private static final Logger LOGGER = Logger.getLogger(LocaleDrivenResourceProvider.class.getName());
+
+    private static synchronized List<LocaleDrivenResourceProvider> getLocaleDrivenResourceProviders() {
+        if (localeDrivenResourceProviders == null) {
+            localeDrivenResourceProviders = new ArrayList<>();
+            for (LocaleDrivenResourceProvider provider : ServiceLoader.load(LocaleDrivenResourceProvider.class)) {
+                localeDrivenResourceProviders.add(provider);
+                LOGGER.log(Level.INFO, "Registered LocaleDrivenResourceProvider: " + provider);
+            }
+        }
+        return localeDrivenResourceProviders;
+    }
+
+    /* package */ static URL lookupResource(String path) {
+        for (LocaleDrivenResourceProvider provider : getLocaleDrivenResourceProviders()) {
+            try {
+                URL url = provider.lookup(path);
+                if (url != null) {
+                    return url;
+                }
+            } catch (Exception e) {
+                LOGGER.log(Level.WARNING, "Failed to look up URL for " + path + " from " + provider, e);
+            }
+        }
+        return null;
+    }
+}

core/src/main/java/org/kohsuke/stapler/Stapler.java

@@ -391,6 +391,10 @@ OpenConnection open(String path, Locale locale, URL fallback) throws IOException
     private final LocaleDrivenResourceSelector resourcePathLocaleSelector = new LocaleDrivenResourceSelector() {
         @Override
         URL map(String path) throws IOException {
+            URL override = LocaleDrivenResourceProvider.lookupResource(path);
+            if (override != null) {
+                return override;
+            }
             return getResource(path);
         }
     };
@@ -409,6 +413,10 @@ private OpenConnection openResourcePathByLocale(HttpServletRequest req,String re
     private final LocaleDrivenResourceSelector urlLocaleSelector = new LocaleDrivenResourceSelector() {
         @Override
         URL map(String url) throws IOException {
+            URL override = LocaleDrivenResourceProvider.lookupResource(url);
+            if (override != null) {
+                return override;
+            }
             return new URL(url);
         }
     };