【标 题】：tomcat5下jsp出现getOutputStream() has already been called for this response异常的原因和解决方法【关键字】：tomcat5,jsp,getOutputStream,has,already,been,called,for,this,response【来 源】：http://blog.csdn.net/alexwan/archive/2007/02/13/1508871.aspx
tomcat5下jsp出现getOutputStream() has already been called for this response异常的原因和解决方法
在tomcat5下jsp中出现此错误一般都是在jsp中使用了输出流（如输出图片验证码，文件下载等），没有妥善处理好的原因。具体的原因就是在tomcat中jsp编译成servlet之后在函数_jspService(HttpServletRequest request, HttpServletResponse response)的最后有一段这样的代码finally { if (_jspxFactory != null) _jspxFactory.releasePageContext(_jspx_page_context); }这里是在释放在jsp中使用的对象，会调用response.getWriter(),因为这个方法是和response.getOutputStream()相冲突的！所以会出现以上这个异常。
然后当然是要提出解决的办法，其实挺简单的（并不是和某些朋友说的那样--将jsp内的所有空格和回车符号所有都删除掉），
在使用完输出流以后调用以下两行代码即可：out.clear();out = pageContext.pushBody();
最后这里是一个输出彩色验证码例子（这样的例子几乎随处可见）imag.jsp
<% @ page import = " java.awt.*,java.awt.image.*,java.util.*,javax.imageio.* " %> <% @ page import = " java.io.OutputStream " %> <%! Color getRandColor( int fc, int bc){Random random = new Random(); if (fc > 255 ) fc = 255 ; if (bc > 255 ) bc = 255 ; int r = fc + random.nextInt(bc - fc); int g = fc + random.nextInt(bc - fc); int b = fc + random.nextInt(bc - fc); return new Color(r,g,b);} %> <% try {response.setHeader( " Pragma " , " No-cache " );response.setHeader( " Cache-Control " , " no-cache " );response.setDateHeader( " Expires " , 0 ); int width = 60 , height = 20 ;BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);OutputStream os = response.getOutputStream();Graphics g = image.getGraphics();Random random = new Random();g.setColor(getRandColor( 200 , 250 ));g.fillRect( 0 , 0 , width, height);g.setFont( new Font( " Times New Roman " ,Font.PLAIN, 18 ));g.setColor(getRandColor( 160 , 200 )); for ( int i = 0 ;i < 155 ;i ++ ){ int x = random.nextInt(width); int y = random.nextInt(height); int xl = random.nextInt( 12 ); int yl = random.nextInt( 12 );g.drawLine(x,y,x + xl,y + yl);}String sRand = "" ; for ( int i = 0 ;i < 4 ;i ++ ){String rand = String.valueOf(random.nextInt( 10 ));sRand += rand;g.setColor( new Color( 20 + random.nextInt( 110 ), 20 + random.nextInt( 110 ), 20 + random.nextInt( 110 )));g.drawString(rand, 13 * i + 6 , 16 );}session.setAttribute( " rand " ,sRand);g.dispose();ImageIO.write(image, " JPEG " ,os);os.flush();os.close();os = null ;response.flushBuffer();out.clear();out = pageContext.pushBody();} catch (IllegalStateException e){System.out.println(e.getMessage());e.printStackTrace();} %>
