ClassNotFoundException: javax.validation.ValidationException
三、问题
nested exception is java.lang.NoClassDefFoundError: javax/validation/ValidationException
原因：项目中没有引用 spring-boot-starter-validation 包
As of #19550,
Web and WebFlux starters do not depend on the validation starter by default anymore.
If your application is using validation features, you’ll need to manually add back a dependency on spring-boot-starter-validation in your build file.
解决方案：
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-validation</artifactId>
</dependency>