ResponseWrapper getOutputStream() not called while retrieving a static resource

[Allen Bandela]

Hello.
My goal: to get to the binary data of the response and cache it. The requests are for zip-files such as /2/005.zip . I'm using an IBM objectgrid as a cache.
My code:

              
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
FileResponseWrapper wrapper = new FileResponseWrapper((HttpServletResponse)response);
		//check cache
		
try{ String key = this.createCacheKey((HttpServletRequest)request);
			if(!cache.containsKey(key)){
				throw new NeedsRefreshException();
			}
			byte[] cByteArray = (byte[])cache.get(key);
			//write cByteArray to response
			ServletOutputStream res = response.getOutputStream();
			res.write(cByteArray);
			res.flush();
        		}catch(NeedsRefreshException n){
				// pass the request along the filter chain
				chain.doFilter(request, wrapper);
				byte []	byteArray1 = wrapper.getReponseContent(); //getting a null pointer exception here. see below for code.
				//insert element into grid
					cache.put(key, byteArray1);
					sess.commit();
}

My response wrapper code:

 
public class FileResponseWrapper extends HttpServletResponseWrapper {
private MyFileServletOutputStream newOutputStream= null;
               //overridden . I'm expecting this method to be called by container when retrieving the zip file. But this is never called. How can I cache the content then.
	public ServletOutputStream getOutputStream(){
		System.out.println("getOutputStream called");
		if(newOutputStream == null){
				newOutputStream = new MyFileServletOutputStream();
		}
		return newOutputStream;
	}
	public byte[] getReponseContent(){
		
		return newOutputStream.getContent(); // this returns a byte[] array of the ServletOutputStream , which I have extended to keep a copy. Just the standard caching mechanism.
	}

How can I get access to the zip-file in the response, in order to cache it.
While debugging, I noticed that the getOutputStream() method of the responsewrapper is not called. I was assuming that the container would call it. All I found while debugging that the responsewrapper had a SRTServletResponse within it that had my file data (mime-type:application/x-zip).