POM中指定编译版本

    <properties>
        <project.build.sourceEncoding>utf-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>utf-8</project.reporting.outputEncoding>   
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>