how to make auto reload with Spring-boot on IDEA Intellij

First, be sure that you added spring-boot-devtools as dependency:

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

Second, verify that the option check-box File->Setting –> Build, Execution, Deployment –> Compiler–>Build project automatically is selected.

Last, press SHIFT+CTRL+A for Linux/Windows users or Command+SHIFT+A for Mac users, then type registry in the opened pop-up window. Scroll down to Registry... using the down arrow key and hit ENTER on Registry.... In the Registry window verify the option compiler.automake.allow.when.app.running is checked.

If the static files are not reloaded, press CTRL+F9 to force a reload.

The instructions above are taken from here