No grammar constraints (DTD or XML Schema) referenced in the document.
在web.xml头部信息中,添加以下内容即可解决问题
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/2002/xmlspec/dtd/2.10/xmlspec.dtd">