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POHow to output a binary document based on a HTML document using filters in Java
 

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  1. POHow to output a binary document based on a HTML document using filters in Java
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    <p>This may be a little confusing but I having some trouble. My goal is to take an input HTML document and then process that document and use the HTML data to output a image document. For example, a user will request a URL, with some action=png in the querystring and then the filter will get invoked for the URL and output image document.</p> <p>I have tried everything but in my environment (Websphere), I am only able to output of one type. If the input type is text/html then I can only output a text document, I can't seem to output a binary document. Why? Because I get an illegal state exception each time.</p> <p>[1/29/09 17:59:57:576 EST] 00000020 SystemErr R java.lang.IllegalStateException: SRVE0209E: Writer already obtained [1/29/09 17:59:57:576 EST] 00000020 SystemErr R at com.ibm.ws.webcontainer.srt.SRTServletResponse.getOutputStream(SRTServletResponse.java:505)</p> <p>I am using pseudo code not to reveal all of my code:</p> <pre><code>&lt;filter&gt; &lt;filter-name&gt;TestFilter&lt;/filter-name&gt; &lt;filter-class&gt; com.util.TestFilter &lt;/filter-class&gt; &lt;/filter&gt; &lt;filter-mapping&gt; &lt;filter-name&gt;TestFilter&lt;/filter-name&gt; &lt;url-pattern&gt;/index_test2.html&lt;/url-pattern&gt; &lt;/filter-mapping&gt; </code></pre> <p>The Wrapper Class code is essentially this:</p> <pre><code>public class ContentCaptureServletResponse extends HttpServletResponseWrapper { private ByteArrayOutputStream contentBuffer; private PrintWriter writer; public PrintWriter getWriter() throws IOException { if (writer == null) { contentBuffer = new ByteArrayOutputStream(); writer = new PrintWriter(contentBuffer); } return writer; } public String getContent(){ try { writer = getWriter(); } catch (IOException e) { e.printStackTrace(); } writer.flush(); String xhtmlContent = new String(contentBuffer.toByteArray()); System.out.println(xhtmlContent); return xhtmlContent; } } </code></pre> <p>And the filter code is this:</p> <pre><code>public void doFilter(ServletRequest req, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; final String renderType = request.getParameter("R"); final String renderClassName = request.getParameter("C"); if ((renderType != null) &amp;&amp; (renderClassName != null)) { try { this.setFilterChain(filterChain); response.setContentType("image/png"); PrintWriter out = response.getWriter(); // I call getWriter but not BOTH! //response.getOutputStream(); response.getWriter(); // Build up the HTML document into a string. CaptureResponse capContent = new CaptureResponse(response); this.mainFilterChain.doFilter(req, ); String myString = capHtmlContent.getContent(); // What I really want to do here is output an output stream // so I can write a binary image processStr(myString); response.getOutputStream(); response.write(binaryimage) } catch (Exception e) { e.printStackTrace(); } // No data will be output to the user. } else { filterChain.doFilter(request, response); } // End of if-else } // End of the method. </code></pre> <p>The code works if I want to take some input html text document. I am assuming because of the open printwriter stream. But I am having trouble going to a different format. Basically, because I can't call response.getOutputStream()</p>
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    1. COI think I might have figured it out. I can use 'response.getOutputstream'. But I had code where the browser would not rebuild the page so it looked like I was a getting a zero response. Basically, my approach will work.
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    2. COCan you explain why you need to use response.getWriter()?
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    3. COActually, I may be a little lost. It looks like this may be a bug with Websphere 6.1/RAD7. On response.getWriter(), I thought I needed it because when I use it, the code worked properly.
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