Cannot create a secure XMLInputFactory

public static String postData1(String urlAddress, String encodedType,Map params) {

try {

URL url = new URL(urlAddress);

URLConnection conn = url.openConnection();
conn.setRequestProperty("accept", "*/*");
conn.setRequestProperty("connection", "Keep-Alive");
conn.setRequestProperty("user-agent",
"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");

        conn.setDoOutput(true);  
        conn.setDoInput(true);  
        conn.setUseCaches(false); // Post请求不用设置缓存  

        conn.getOutputStream();

        // 获取返回数据  
        BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream(), "utf-8"));  
        String line = null;  
        StringBuffer sb = new StringBuffer();  
        while ((line = in.readLine()) != null) {  
            sb.append(line);  
        }  
        in.close(); // 关闭流  
        return sb.toString();  
    } catch (Exception e) {  
        e.printStackTrace();  
    }  
    return "";  
}  
    使用上述的代码访问webservice，如果不加conn.getOutputStream()，返回soap协议正确，如果加上这一句，报错500，服务器那边显示错误：不能创建一个安全的xmlInputFactory：java.lang.RuntimeException: Cannot create a secure XMLInputFactory。
    这是什么原因呢？在线等待，大家帮帮忙......