jsp 图片 验证码 getOutputStream() has already been called for this response 问题的解决

在写JSP程序的时候，如果程序中调用了response.getOutputStream()去向客户端输出文件等数据流,容器就会抛出这样的异常：
Java.lang.IllegalStateException: getOutputStream() has already been called for this response
at org.apache.catalina.connector.Response.getWriter(Response.java:596)
at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:186)
产生这样的异常原因:是web容器生成的servlet代码中有out.write(""),这个和JSP中调用的response.getOutputStream()产生冲突.即Servlet规范说明，不能既调用response.getOutputStream()，又调用response.getWriter(),无论先调用哪一个，在调用第二个时候应会抛出IllegalStateException，因为在jsp中，out变量实际上是通过response.getWriter得到的，你的程序中既用了response.getOutputStream，又用了out变量，故出现以上错误。

解决方案：在程序的最后添加：
out.clear();
out = pageContext.pushBody();
就可以了。

<%@ page contentType="image/jpeg" import="java.io.OutputStream,java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*,com.sun.image.codec.jpeg.JPEGCodec,com.sun.image.codec.jpeg.JPEGImageEncoder;"%><%!
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);
}
%><%
response.reset();
//
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);
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(new Color());
//g.drawRect(0,0,width-1,height-1);
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);
}
//
request.getSession().setAttribute("checkcode",sRand);
//
g.dispose();
//
OutputStream output=response.getOutputStream();
response.flushBuffer();
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(output);
encoder.encode(image);
out.clear();
out = pageContext.pushBody();%>

 

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