在导入或新建一些项目的时候，有时候会出现一些问题，如Diamond types are not supported at language level '5'错误，但是通过idea的Project Structure设置后发现每次刷新都会重置回原来的级别，设置无效果，可以通过pom来指定Language level级别，如下所示：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.yc</groupId>
    <artifactId>industrial-application-bed</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>industrial-application-bed</name>
    <description>Demo project for Spring Boot</description>

<dependencies>
	<!--依赖坐标-->
</dependencies>

<!--指定Language Level级别-->
<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>8</source>
                    <target>8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

如图：