response.getOutputStream() throws IllegalStateException when called for the first time

Question

I'm trying to Download a pdf from a MySQL-DB ( I get it as a Blob, and up to that point everything works just fine. But when I try to get the ServletOutputstream to send it to the client the programm crashes.

AFAIK the exception is thrown when the method has been called before or the getwriter-method has. But I don't use the getwriter-method in my code at all and the other getOutPutStream-methods in the programm are not reached (I commented them out to make sure).
(The whole thing happens in a JSP if that matters for any reason)

Heres my code snippet and the Exception:

Code

Blob pdf = null;
if(request.getParameter("reportId") != null){
    pdf = testszenario.getReportErgebnisPdf(Integer.parseInt(request.getParameter("reportId")), request.getParameter("erzeugung"));
}
byte[] buf = new byte[(int)pdf.length()];
InputStream inputStream  = pdf.getBinaryStream();
inputStream.read(buf);
inputStream.close();
response.setContentType("application/pdf");
response.setHeader("Content-disposition","attachment; filename=test.pdf"); 

ServletOutputStream sos = response.getOutputStream();
// response.getOutputStream().write(buf);

Exception

26.03.2013 09:28:29 org.apache.catalina.core.ApplicationDispatcher invoke
SCHWERWIEGEND: Servlet.service() for servlet jsp threw exception
java.lang.IllegalStateException
    at org.apache.jasper.runtime.ServletResponseWrapperInclude.getOutputStream(ServletResponseWrapperInclude.java:63)
    at org.apache.jsp.jsp.modules.Testszenario.PostReportResultOverview_jsp._jspService(PostReportResultOverview_jsp.java:115)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:630)
    at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:535)
    at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:472)
    at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)
    at org.apache.jsp.jsp.McFrame_jsp._jspService(McFrame_jsp.java:284)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Thread.java:619)

Answer 1

Please check if your response is committed. If you try to do something on a committed response then IllegalStateException may arise. Response will be committed, if page buffer size is exceeded.

Answer 2

It might indeed matter that you're doing this in a JSP. Keep in mind that the JSP is part of the output rendering phase of a web application request, so the container might have obtained the writer object already. Try moving your code into a servlet instead. It'll give you more control over the writer/streams.