1、先设置pom.xml文件，加入依赖

1.1、在dependencies标签里加入

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

1.2、在plugins标签下加入

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>
    <fork>true</fork>
    <addResources>true</addResources>
  </configuration>
</plugin>

2、设置idea

2.1、file->settings->compiler，勾选如图选项

2.2、press ctrl+shift+Alt+/,选择Registry

2.3、选择下图选项

3、重启idea生效