Content is not allowed in prolog

<%@ page contentType="text/html; charset=gb2312" language="java" errorPage="" %>

<%
java.io.BufferedReader rd = request.getReader();
String str = null;

str = rd.readLine();

org.w3c.dom.Document xmlDoc = null;
xmlDoc = javax.xml.parsers.DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new java.io.ByteArrayInputStream(str.getBytes()));
org.w3c.dom.NodeList selectedPetTypes = xmlDoc.getElementsByTagName("type");
String type = null;
String responseText = "Selected Pets: ";
for(int i=0; i<selectedPetTypes.getLength(); i++)
{
type = selectedPetTypes.item(i).getFirstChild().getNodeValue();
responseText = responseText + " " + type;
}
out.println(responseText);
%>

以上是我的JSP代码,在遨游,IE下ajax请求url的时候能正确输出结果,在firefox下请求url面时就错误代码500,如果采用form提交无论什么浏览器都会出现这个提示: Content is not allowed in prol

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