Strong algorithms, data structures and coding background especially in Java and Scala; Development experience on the JVM, including asynchronous I/O, concurrency, and the Java memory model. Familiar with debugging tools such as JStack, JMap, JHat, gdb.
Experience with software engineering best practices (e.g. unit testing, code reviews, design documentation, tdd) and disciplined approach to testing, quality assurance and documentation
Expert knowledge of Java (1.5) and the Wicket web framework. Experience with web infrastructure, distributed systems and message driven architecture
A history of open-source contribution.
some additional keywords/skills: HornetQ, ActiveMQ, Cassandra, Mysql, MariaDB, MongoDB, CouchDB, neo4j, Memcache, nginx, apache, netty, tomcat, vert.x, Play!, Hadoop, Elasticsearch, Akka, Spring, Ebean, Siena, Hibernate