What are the must learn and popular technology for web service ?

Good day,

May i know what are the current trend and MUST learn for a newbie on Web Service ? there are many technology around and i'm confusing which to start picking

Start by learning about REST, and then move on to the JAX-RS API (the standard Java API for RESTful WS) and its reference implementation Jersey: https://www.coderanch.com/how-to/java/WebServicesFaq

Thanks Ulf Dittmer , may I know what are the REST web server are popular use ?

Jersey. It's a Java web app that runs in any standard servlet container.

Thanks again Ulf Dittmer for enlighten me