jsp图片验证码实现及getOutputStream() has already been called for this response异常
2008-10-09 08:50
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jsp图片验证码实现及getOutputStream() has already been called for this response异常
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)
VerifyCode.jsp
<meta http-equiv="Content-Type" content="text/html; charset=GBK"><%@ page contentType="text/html; charset=GBK" language="java"%><%@ page import="javax.imageio.ImageIO,java.io.OutputStream"%>
<%! // String of VerifyCode // @author Rongdajian String sVerifyCode;%>
<% response.setHeader("Pragma","No-cache"); response.setHeader("Cache-Control","no-cache"); response.setDateHeader("Expires", 0); response.reset(); try{ cn.softjob.util.VerifyCode VC = new cn.softjob.util.VerifyCode(); session.setAttribute("VerifyCode",VC.runVerifyCode(4)); //session.setMaxInactiveInterval(60); sVerifyCode = (String)session.getAttribute("VerifyCode"); OutputStream outs = response.getOutputStream(); ImageIO.write(VC.CreateImage(sVerifyCode),"JPEG",outs); outs.flush() ; outs.close(); outs = null ; out.clear() ; out = pageContext.pushBody(); }catch(IllegalStateException e){ System.out.println(e.getMessage()); e.printStackTrace(); return; } %>
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)
VerifyCode.jsp
<meta http-equiv="Content-Type" content="text/html; charset=GBK"><%@ page contentType="text/html; charset=GBK" language="java"%><%@ page import="javax.imageio.ImageIO,java.io.OutputStream"%>
<%! // String of VerifyCode // @author Rongdajian String sVerifyCode;%>
<% response.setHeader("Pragma","No-cache"); response.setHeader("Cache-Control","no-cache"); response.setDateHeader("Expires", 0); response.reset(); try{ cn.softjob.util.VerifyCode VC = new cn.softjob.util.VerifyCode(); session.setAttribute("VerifyCode",VC.runVerifyCode(4)); //session.setMaxInactiveInterval(60); sVerifyCode = (String)session.getAttribute("VerifyCode"); OutputStream outs = response.getOutputStream(); ImageIO.write(VC.CreateImage(sVerifyCode),"JPEG",outs); outs.flush() ; outs.close(); outs = null ; out.clear() ; out = pageContext.pushBody(); }catch(IllegalStateException e){ System.out.println(e.getMessage()); e.printStackTrace(); return; } %>
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