Struts 2 discard cache header

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

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.

Answer 2

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.