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PODifferences between ServletResponse and HttpServletResponseWrapper?
 

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  1. PODifferences between ServletResponse and HttpServletResponseWrapper?
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    <p>I am new to servlet and reading some text about filters and wrappers. I can understand filters but got confused about wrappers. In the book, the author gives an example:</p> <p>In case no wrapper:</p> <pre><code>public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { String name = request.getParameter("name").trim(); try { chain.doFilter(request, response); PrintWriter out = response.getWriter(); if (name.length() == 0) { out.println("Some message"); out.println("&lt;/body&gt;"); out.println("&lt;/html&gt;"); out.close(); } } catch (Throwable t) { } } </code></pre> <p>In case of wrapper:</p> <pre><code> public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { String name = request.getParameter("name").trim(); HttpServletResponse httpRes = (HttpServletResponse) response; HttpServletResponseWrapper resWrapper = new HttpServletResponseWrapper(httpRes); try { chain.doFilter(request, response); PrintWriter out = resWrapper.getWriter(); // why dont we just use response.getWriter(); if (name.length() == 0) { out.println("&lt;h3&gt;Some message"); out.println("&lt;/body&gt;"); out.println("&lt;/html&gt;"); out.close(); } } catch (Throwable t) { } } </code></pre> <p>Why we need <code>HttpServletResponseWrapper</code> while we can do the same thing with <code>ServletResponse</code> in case 1? Can anyone give me a clear example that we MUST use <code>HttpServletResponseWrapper</code> instead of <code>ServletResponse</code>? I have tried to google but found no luck.</p>
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    1. COThis code looks weird. The purpose of wrapping servlet response is to pass it further (`chain.doFilter(request, resWrapper);`) and intercept selected calls in the wrapper. This way you can, for instance, return different response writer that changes or compresses the content on the fly and sends it to the target `response`. This example doesn't have much sense... Could you provide the source of this (page, book?)
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      1. USTomasz Nurkiewicz
    2. COI found myself weird too. This code I took from a powerpoint slide of a University lecturer. It makes more sense if we do chain.doFilter(request, resWrapper); as your suggestion
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