I have same problem for me adding

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

under the spring-boot-starter-web dependency solved problem. To be sure you should generate dependency directly with Validation form start spring io. It's worth mentioning that order of dependencies in pom file is crucial

I had same problem For me adding:

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

under the spring-boot-starter-web dependency solved problem. To be sure you should generate dependency directly with Validation form start spring io. It's worth mentioning that order of dependencies in pom file is crucial