Add getCacheTime(filename) to VaadinServlet (#11744)

This implementation by default adheres to the GWT Pristine Caching rules
and calculates 0 seconds for ".nocache." and 1 year for ".cache."
filenames. All other filenames will use the value configured in the
deployment configuration.
By exposing this to a method, developers can implement custom naming
schemes. Developers also can opt to set an expires header using this
value.

Change-Id: Ibc0d17d48d38bfa3bb28bdf3929ad314828be406

1 files changed, 42 insertions, 15 deletions

diff --git a/server/src/com/vaadin/server/VaadinServlet.java b/server/src/com/vaadin/server/VaadinServlet.java
index a9eb42578e..43bcb3d394 100644
--- a/server/src/com/vaadin/server/VaadinServlet.java
+++ b/server/src/com/vaadin/server/VaadinServlet.java
@@ -670,21 +670,11 @@ public class VaadinServlet extends HttpServlet implements Constants {
         // Provide modification timestamp to the browser if it is known.
         if (lastModifiedTime > 0) {
             response.setDateHeader("Last-Modified", lastModifiedTime);
-            /*
-             * The browser is allowed to cache for 1 hour without checking if
-             * the file has changed. This forces browsers to fetch a new version
-             * when the Vaadin version is updated. This will cause more requests
-             * to the servlet than without this but for high volume sites the
-             * static files should never be served through the servlet. The
-             * cache timeout can be configured by setting the resourceCacheTime
-             * parameter in web.xml
-             */
-            int resourceCacheTime = getService().getDeploymentConfiguration()
-                    .getResourceCacheTime();
-            String cacheControl = "max-age="
-                    + String.valueOf(resourceCacheTime);
-            if (filename.contains("nocache")) {
-                cacheControl = "public, max-age=0, must-revalidate";
+
+            String cacheControl = "public, max-age=0, must-revalidate";
+            int resourceCacheTime = getCacheTime(filename);
+            if (resourceCacheTime > 0) {
+                cacheControl = "max-age=" + String.valueOf(resourceCacheTime);
             }
             response.setHeader("Cache-Control", cacheControl);
         }
@@ -693,6 +683,43 @@ public class VaadinServlet extends HttpServlet implements Constants {
     }
 
     /**
+     * Calculates the cache lifetime for the given filename in seconds. By
+     * default filenames containing ".nocache." return 0, filenames containing
+     * ".cache." return one year, all other return the value defined in the
+     * web.xml using resourceCacheTime (defaults to 1 hour).
+     * 
+     * @param filename
+     * @return cache lifetime for the given filename in seconds
+     */
+    protected int getCacheTime(String filename) {
+        /*
+         * GWT conventions:
+         * 
+         * - files containing .nocache. will not be cached.
+         * 
+         * - files containing .cache. will be cached for one year.
+         * 
+         * https://developers.google.com/web-toolkit/doc/latest/
+         * DevGuideCompilingAndDebugging#perfect_caching
+         */
+        if (filename.contains(".nocache.")) {
+            return 0;
+        }
+        if (filename.contains(".cache.")) {
+            return 60 * 60 * 24 * 365;
+        }
+        /*
+         * For all other files, the browser is allowed to cache for 1 hour
+         * without checking if the file has changed. This forces browsers to
+         * fetch a new version when the Vaadin version is updated. This will
+         * cause more requests to the servlet than without this but for high
+         * volume sites the static files should never be served through the
+         * servlet.
+         */
+        return getService().getDeploymentConfiguration().getResourceCacheTime();
+    }
+
+    /**
      * Writes the contents of the given resourceUrl in the response. Can be
      * overridden to add/modify response headers and similar.
      *