Servlet class is not recognized as a servlet

Issue

• Getting error when deploying war file Servlet class does not implement javax.servlet.Servlet
• War file is deploying in EAP6 but giving error in EAP7

boss.undertow.deployment.default-server.default-host./helloworld.UndertowDeploymentInfoService: org.jboss.msc.service.StartException in service jboss.undertow.deployment.default-server.default-host./helloworld.UndertowDeploymentInfoService: Failed to start service
        at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1904)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.IllegalArgumentException: UT010009: Servlet com.abc.HelloWorld of type class com.abc.HelloWorld does not implement javax.servlet.Servlet