RESTFul web services are the most popular trends in modern time.
Here are some important reference links to develop these services in Java:

[Official Tutorial]
http://docs.oracle.com/javaee/6/tutorial/doc/giepu.html

[Spring-Framework for RESTFul Support]
Search RestTemplate OR check REST Support in MVC Section
http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/
http://spring.io/guides/gs/rest-service/

[Other Reference]
http://java.dzone.com/articles/restful-web-services-java
http://www.vogella.com/tutorials/REST/article.html

Enjoy Reading.