Question

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.

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.

[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)

I am using pseudo code not to reveal all of my code:

<filter>     <filter-name>TestFilter</filter-name>     <filter-class>         com.util.TestFilter     </filter-class> </filter>  <filter-mapping>     <filter-name>TestFilter</filter-name>     <url-pattern>/index_test2.html</url-pattern> </filter-mapping> 

The Wrapper Class code is essentially this:

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;      } } 

And the filter code is this:

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) && (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. 

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()

Answer 1

The issue does appear to be that you are opening the response Writer prior to wrapping the response.

It looks like you should be able to do:

this.setFilterChain(filterChain); CaptureContent capContent = new CaptureResponse(response); doFilter() process(); response.setContentType('image/png'); response.getOutputStream().write(imagedata); 

You definitely cannot safely open both the Writer and the OutputStream