<%
    Enumeration attributeNames = request.getAttributeNames();
    while (attributeNames.hasMoreElements())
    {
        String attributeName = attributeNames.nextElement();
        Object attribute = request.getAttribute(attributeName);
   out.println("request.attribute['" + attributeName + "'] = " + attribute); 
    }
%>

代码中输出了所有的 request 中的变量。从中也可以看到访问哪个文件出错，跳到哪个错误页面了，从而进行更详细、更人性化的错误处理。例如，提示可能的正确网址等等。

例如：访问一个不存在的页面 page_not_exist.html，显示的信息为：

request.attribute['javax.servlet.forward.request_uri'] = /page_not_exists.html

request.attribute['javax.servlet.forward.context_path'] = 

request.attribute['javax.servlet.forward.servlet_path'] = /page_not_exists.html

request.attribute['javax.servlet.forward.path_info'] = /errorpages/404.jsp

request.attribute['javax.servlet.error.message'] = /page_not_exists.html

request.attribute['javax.servlet.error.status_code'] = 404

request.attribute['javax.servlet.error.servlet_name'] = default

request.attribute['javax.servlet.error.request_uri'] = /page_not_exists.html

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