set Cache-Control and Expires header even when not-modified (#8757)

Usually first a resource is served with the lower code block. this
provides cache-control, expires and last-modification headers to the
browser. But when a not-modified response was served, these headers
were missing. This effectively caused the caching to no longer work once
the not-modified responses are sent out.

Change-Id: I9b1f0cacc91734f88bb0384872da0d426d4b5fe0

1 files changed, 10 insertions, 12 deletions

diff --git a/server/src/com/vaadin/server/VaadinServlet.java b/server/src/com/vaadin/server/VaadinServlet.java
index 4656f9a672..4fd1e97a40 100644
--- a/server/src/com/vaadin/server/VaadinServlet.java
+++ b/server/src/com/vaadin/server/VaadinServlet.java
@@ -704,6 +704,15 @@ public class VaadinServlet extends HttpServlet implements Constants {
             return;
         }
 
+        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);
+        response.setDateHeader("Expires", System.currentTimeMillis()
+                + (resourceCacheTime * 1000));
+
         // Find the modification timestamp
         long lastModifiedTime = 0;
         URLConnection connection = null;
@@ -714,6 +723,7 @@ public class VaadinServlet extends HttpServlet implements Constants {
             // are not returned by the browser in the "If-Modified-Since"
             // header).
             lastModifiedTime = lastModifiedTime - lastModifiedTime % 1000;
+            response.setDateHeader("Last-Modified", lastModifiedTime);
 
             if (browserHasNewestVersion(request, lastModifiedTime)) {
                 response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
@@ -748,18 +758,6 @@ public class VaadinServlet extends HttpServlet implements Constants {
             response.setContentType(mimetype);
         }
 
-        // Provide modification timestamp to the browser if it is known.
-        if (lastModifiedTime > 0) {
-            response.setDateHeader("Last-Modified", lastModifiedTime);
-
-            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);
-        }
-
         writeStaticResourceResponse(request, response, resourceUrl);
     }