Web and WebFlux starters do not depend on the validation starter by default anymore in SpringBoot 2.3. If your application is using validation features, for example you find that javax.validation.* imports are not being resolved, you’ll need to add the starter yourself.

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-validation</artifactId>
</dependency>

See: https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-2.3-Release-Notes#validation-starter-no-longer-included-in-web-starters