title: How to enable browser caching in GAE
body: <p>Although this question should be trivial, I didn't success to enable browser caching on web google app engine java server.</p>
  
  <p>I've try to put this kind of thing in my appengine-web.xml:</p>
  
  <pre><code>&lt;static-files&gt;
    &lt;include path="/**.cache.**" expiration="365d" /&gt;
  ...
  </code></pre>
  
  <p>but when I'm looking the response header I find this in local:</p>
  
  <pre><code>Content-Length: 196084
  Cache-Control: public, max-age=31536000
  Expires: Fri, 10 Jan 2014 19:40:45 GMT
  Content-Type: image/png
  Last-Modified: Tue, 18 Dec 2012 21:41:22 GMT
  Server: Jetty(6.1.x)
  </code></pre>
  
  <p>Which is fine... but this in production environment:</p>
  
  <pre><code>HTTP/1.1 304 Not Modified
  ETag: "RV4Bpg"
  X-AppEngine-Estimated-CPM-US-Dollars: $0.000000
  X-AppEngine-Resource-Usage: ms=109 cpu_ms=0
  Date: Thu, 10 Jan 2013 19:41:20 GMT
  Pragma: no-cache
  Expires: Fri, 01 Jan 1990 00:00:00 GMT
  Cache-Control: no-cache, must-revalidate
  Server: Google Frontend
  </code></pre>
  
  <p>Which is definitively not what I want :(</p>
  
  <p>Any idea ? something I've missed ?</p>
  
  <p><strong>[EDIT]</strong>
  for not yet downloaded content, my browser receive the following header:</p>
  
  <pre><code>HTTP/1.1 200 OK
  ETag: "RV4Bpg"
  Date: Fri, 11 Jan 2013 12:50:50 GMT
  Expires: Sat, 11 Jan 2014 12:50:50 GMT
  Cache-Control: public, max-age=31536000
  X-AppEngine-Estimated-CPM-US-Dollars: $0.000000
  X-AppEngine-Resource-Usage: ms=3 cpu_ms=0
  Date: Fri, 11 Jan 2013 12:50:50 GMT
  Pragma: no-cache
  Expires: Fri, 01 Jan 1990 00:00:00 GMT
  Cache-Control: no-cache, must-revalidate
  Content-Type: image/png
  Server: Google Frontend
  Content-Length: 196084
  Proxy-Connection: Keep-Alive
  Connection: Keep-Alive
  X-RBT-Optimized-By: eu-dcc-sh02 (RiOS 6.5.5b) SC
  </code></pre>
  
  <p>An ETag and several contradictory 'Expires' and 'Cache-Control' ...
  Is there several way to configure caching policy ? Could it come from my ISP ? or a proxy ?</p>