Struts 2 discard cache header - caching

Question

I have strange discarding behavior of struts2 while setting cache option for my image.
I'm trying to put image from db to be cached on client side
To render image I use ( http://struts.apache.org/2.x/docs/how-can-we-display-dynamic-or-static-images-that-can-be-provided-as-an-array-of-bytes.html ) where special result type render as follow:
public void execute(ActionInvocation invocation) throws Exception {
...//some preparation
HttpServletResponse response = ServletActionContext.getResponse();
HttpServletRequest request = ServletActionContext.getRequest();
ServletOutputStream os = response.getOutputStream();
try
{
byte[] imageBytes = action.getImage();
response.setContentType("image/gif");
response.setContentLength(imageBytes.length);
//I want cache up to 10 min
Date future = new Date(((new Date()).getTime() + 1000 * 10*60l));
;
response.addDateHeader("Expires", future.getTime());
response.setHeader("Cache-Control", "max-age=" + 10*60 + "");
response.addHeader("cache-Control", "public");
response.setHeader("ETag", request.getRequestURI());
os.write(imageBytes);
}
catch(Exception e)
{
response.sendError(HttpServletResponse.SC_NOT_FOUND);
}
os.flush();
os.close();
}
But when image is embedded to page it is always reloaded (Firebug shows code 200), and neither Expires, nor max-age are presented in header
Host localhost:9090
Accept image/png,image/*;q=0.8,*/*;q=0.5
Accept-Language en-us,en;q=0.5
Accept-Encoding gzip,deflate
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive 300
Connection keep-alive
Referer http://localhost:9090/web/result?matchId=1
Cookie JSESSIONID=4156BEED69CAB0B84D950932AB9EA1AC;
If-None-Match /web/_srv/teamcolor
Cache-Control max-age=0
I have no idea why it is dissapered, may be problem in url? It is forms with parameter:
http://localhost:9090/web/_srv/teamcolor?loginId=3

Answer 1

At last I've discovered what wrong with my code, it is rather strange because it is partially works (image is displayed).
The culprit is following line:
HttpServletResponse response = ServletActionContext.getResponse();
It must be replaced with following:
HttpServletResponse response = (HttpServletResponse)
invocation.getInvocationContext().get(StrutsStatics.HTTP_RESPONSE);
It is looks like kind of magic, but obviously both response shares the same output stream but not the container of header declarations.

Answer 2

Not sure if this would work any better, but you could try. Create a custom interceptor that modifies the response headers. Something like this (note, I haven't tested this):
package com.yourpackage.interceptor;
import java.util.Date;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts2.StrutsStatics;
import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionInvocation;
import com.opensymphony.xwork2.interceptor.AbstractInterceptor;
public class ResponseHeadersInterceptor extends AbstractInterceptor {
#Override
public String intercept(ActionInvocation invocation) throws Exception {
ActionContext context = invocation.getInvocationContext();
HttpServletResponse response = (HttpServletResponse)context.get(StrutsStatics.HTTP_RESPONSE);
HttpServletRequest request = (HttpServletRequest)context.get(StrutsStatics.HTTP_REQUEST);
if (response!=null) {
Date future = new Date(((new Date()).getTime() + 1000 * 10*60l));
response.addDateHeader("Expires", future.getTime());
response.setHeader("Cache-Control", "max-age=" + 10*60 + "");
response.addHeader("cache-Control", "public");
if (request!=null)
response.setHeader("ETag", request.getRequestURI());
}
return invocation.invoke();
}
}
Then in your struts.xml, define the interceptor and a new interceptor stack:
<interceptors>
<interceptor name="responseHeaders" class="com.yourpackage.interceptor.ResponseHeadersInterceptor" />
<interceptor-stack name="extendedStack">
<interceptor-ref name="defaultStack" />
<interceptor-ref name="responseHeaders" />
</interceptor-stack>
</interceptors>
Then modify your action definition to use the extendedStack.