package javax.validation.constraints does not exist

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