Agree with Sajux. I've used Apache Oltu in my project for Spring Security OAuth2 implementation and works very greatly. The latest release Version (1.0.0) release in March-14. It has the major 12 usage listed here: http://mvnrepository.com/artifact/org.apache.oltu.oauth2/org.apache.oltu.oauth2.client/1.0.0/usages
The Maven dependency:
<dependency>
<groupId>org.apache.oltu.oauth2</groupId>
<artifactId>org.apache.oltu.oauth2.client</artifactId>
<version>1.0.0</version>
</dependency>
Gradle Dependency:
'org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:1.0.0'
You can refer quick start guide from development perspective. Here you go: https://cwiki.apache.org/confluence/display/OLTU/OAuth+2.0+Client+Quickstart