code: public ServletOutputStream getOutputStream() 
      {
          if (_outputState==DISABLED)
              return __nullServletOut;
          
          if (_outputState!=NO_OUT && _outputState!=OUTPUTSTREAM_OUT)
              throw new IllegalStateException();
          
          if (_writer!=null)
          {
              _writer.flush();
              _writer.disable();
              _writer=null;
          }
          
          if (_out==null)
              _out = new ServletOut(_servletHttpRequest.getHttpRequest()
                                    .getOutputStream());  
          _outputState=OUTPUTSTREAM_OUT;
          return _out;
      }
docs: /* ------------------------------------------------------------