Is there any API in Java to access wikipedia data

I had the same question and the closest I came to an out-of-the-box solution is bliki, hosted at http://code.google.com/p/gwtwiki/. I also wrote an article at Integrating Stuff to help you get started with it: http://www.integratingstuff.com/2012/04/06/hook-into-wikipedia-using-java-and-the-mediawiki-api/

You can use Jwiki to get Wikipedia data Example :

Jwiki jwiki = new Jwiki("elon musk");
System.out.println("Title :"+jwiki.getDisplayTitle()); //get title
System.out.println("Text : "+jwiki.getExtractText());  //get summary text
System.out.println("Image : "+jwiki.getImageURL());    //get image URL

MediaWiki is a free and open-source wiki software. Originally developed by Magnus Manske and improved by Lee Daniel Crocker, it runs on many websites, including Wikipedia, Wiktionary and Wikimedia Commons.[5][6]

There is list of Java libraries that can help you to connect wiki by java code . https://www.mediawiki.org/wiki/API:Client_code#Java

but after use some of them because of their limitations , we try to call REST services from mediawiki directly.