JSR 286 Exercise 5 Solution

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        <expiration-cache>600</expiration-cache>
        <cache-scope>private</cache-scope>
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        if (request.getETag() != null) {
            System.out.println("Expiration Tag is: "+request.getETag());
            if (request.getETag().equals(currentCacheTag)) {
                response.getCacheControl().setExpirationTime(20);
                response.getCacheControl().setUseCachedContent(true);
                return;
            }
        } else {
            System.out.println("Expiration Tag is null");
        }

        // create new content with new validation tag
        session.setAttribute(CACHE_ETAG, CACHE_ETAG);
        response.getCacheControl().setETag(CACHE_ETAG);
        response.getCacheControl().setExpirationTime(20);
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