sonar-maven-plugin:2.6:sonar: java.lang.UnsupportedClassVersionError: org/sonar/api/utils/SonarException : Unsupported major.minor version 52.0

This issue can be resolved by adding JDK version to 1.8 in POm.xml

Please apply the below fix in POM.xml

<build>
    <finalName>appname</finalName>
  <plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
     <artifactId>maven-compiler-plugin</artifactId>
     <version>3.6.1</version>
     <configuration>
     <source>1.8</source>
     <target>1.8</target>
     </configuration>
  </plugin>
  <plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>sonar-maven-plugin</artifactId>
    <version>2.6</version>
  </plugin>
</plugins>
  </build>