IntelliJ Idea

Include the dependency in pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
    <optional>true</optional>
</dependency>

Navigate to Settings → Build, Execution, Deployment → Compiler:

Enable Build project automatically Navigate to Settings → Advanced Settings:

Enable Allow auto-make to start even if the developed application is currently running.