org.xml.sax.SAXParseException: schema_reference.4: Failed to read schema document 'http://code.alibabatech.com/schema/dubbo/dubbo.xsd', because 1) could not find the document; 2) the document could not be read; 3) the root element of the document is not <xsd:schema>.
解决方案
下载dubbo.xsd文件并将改文件添加到XML catalog element 中key值为xml文件中的连接，location为下载的文件路径
如果还不行进行如下操作
解决方案：
添加dubbo框架的jar包
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>dubbo</artifactId>
<version>2.5.5</version>
</dependency>