[java] IntelliJ: Error:java: error: release version 5 not supported

Within IntelliJ, open pom.xml file.

Add this section before <dependencies> (if your file already has a <properties> section, just add the <maven.compiler...> lines below to that existing section):

<properties> 
   <maven.compiler.source>1.8</maven.compiler.source> 
   <maven.compiler.target>1.8</maven.compiler.target> 
</properties>