严重: Servlet.service() for servlet jsp threw exception java.lang.IllegalStateException: getOutputStream() has already been called

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();

}%>