#thymeleaf
spring.thymeleaf.prefix=classpath:/templates/
spring.thymeleaf.suffix=.html
spring.thymeleaf.cache=false
spring.thymeleaf.content-type=text/html
spring.thymeleaf.enabled=true
spring.thymeleaf.encoding=UTF-8
spring.thymeleaf.mode=HTML5
解决办法：注释掉
#spring.thymeleaf.mode=HTML5
Template mode "HTML5 " has not been configured
原文：https://www.cnblogs.com/523823-wu/p/9078688.html