Operative's tech stack is mostly Java/Spring/Hibernate/mysql(innodb)/Hadoop
Phone screen: Mostly basics about java collections, design patterns, spring and hibernate. some questions about resume.
OnSite: Met with about 7-8 people, 3+ hours. Interviewed with CTO, Director of Engineering, some senior developers, and some junior as well. Questions ranged from basic java collection, concurrency/synchronization, design patterns, spring/hibernate, "tell me about this on your resume" to some abstract system design questions.