Cannot access javax.servlet.Filter; class file for javax.servlet.Filter not found

The article which you have shared asks you to add web dependency which i dont see in your pom.xml file. Add the below dependency which should solve the javax.servlet error

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

If you check within the spring-boot-starter-web pom file you will see a dependency to javax.servlet-api - 3.1.0.