tomcat5下jsp出现getOutputStream() has already been called for this response异常的原因和解决方法

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();}%>

如有不足之处，欢迎斧正！