打开Java Resources/Libraries/hibernate-core-5.3.1.Final.jar/org.hibernate/hibernate-mapping-3.0.dtd（hibernate-mapping-3.0.dtd在org.hibernate包中最底下）在该文件中可找到DTD约束

解压hibernate.jar包

在org\hibernate目录下找到hibernate-configuration-3.0.dtd和hibernate-mapping-3.0.dtd

打开Eclipse-->Window-->Preferences-->Web and XML-->XML Catalog

在右边点击Add XML Catalog Entry

Key Type：URL

Key：打开dtd文件粘贴如下路径

http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd

http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd

整个项目刷新一下,输入第一个文档节点就会自动提示

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"

"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

	<class>

		<id>

			<generator class=""></generator>

		</id>

	</class>

</hibernate-mapping>