解决方法：加上 <!DOCTYPE xml>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xml>
<ROOT>
<goods>
<isin>SN100001</isin>
<quantity>1100</quantity>
<price>200.20</price>
<customer>张三</customer>
</goods>
</ROOT>
如何解决XML文件中的警告提示“No grammar constraints (DTD or XML Schema) referenced in the document.”
原文：http://www.cnblogs.com/vincent4code/p/5325378.html
