Idea version 2121.2.1

1. JDK configuration problem

Setting project jdk

Setting module jdk

During the setting of compiler jdkthe clean operation was performed after several settings, resulting in @override error. Later, it was found that the compiler was not checked

use compiler from module target JDK when possible

2. Add in POM file

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>
<build>
    <plugins>
        <plugin>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>8</source>
                <target>8</target>
            </configuration>
        </plugin>
    </plugins>
</build>

Done!