Rename the file spring-cloud-starter-huawei-service-engine-gateway-1.11.0-2022.0.x-javadoc.jar to spring-cloud-starter-huawei-service-engine-gateway-1.11.0-2022.0.x-javadoc.zip
Use your favourite unzip tool (WinRAR / WinZIP) to extract it, now you have a folder spring-cloud-starter-huawei-service-engine-gateway-1.11.0-2022.0.x-javadoc
Double click index.html will open the index page on your default web browser.