Updated: to describe the question more clearly
I create a web applicaiton with spring boot and thymeleaf, everything works fine if I open the login page, then login, then head for the management module or reports module sequently. 
The proleam occurs when I type the url locahost:8080/send/kf/index(needs to authenticate, but I have open access to all in customized filter) in the browser, the page loads without js and css. In debug mode, I saw /send/kf was unexpectly put into the path like the following. I can get the resource if I access localhost:8080/assets/avatars/avatar.png. 
The following is the folder structure I put my static resources. How could /send/kf automatically added into the url, please help me solve this problem. Thanks!

