This is a short description of the Java implementation for the News Recommender Systems challenge hosted by plista. We outline the essential components. Additionally, we emphasise on how to incorporate your own recommender.

• Client.java
• ContestHandler.java
• RecommendedItem.java
• RecommenderItemTable.java
• DirtyRingBuffer.java

The communication is handled by Client.java and ContestHandler.java. The Client.java receives the messages and forwards their contents to the ContestHandler.java who delegates the messages to the suited methods. There are four basic types of messages:

• Item updates
• Recommendation Request
• Notifications (impressions, clicks)
• Errors

Those message types are encoded as HTTP-POST-Parameter. The Client.java extracts the type information. Subsequently, the ContestHandler.java initiates the pre-defined way to handle the request.

The implementation includes a baseline recommender. Considering recency as the most important factor represents the basic idea of the baseline. Each publisher (identified by context.simple.27) is assigned a list of fixed size. As new items arrive - either by updates/creates or through notifications (clicks/impressions) - the item Ids (identified by context.simple.25) are added to the list. Upon incoming recommendation requests, the DirtyRingBuffer.java returns the N most recent items. N refers to the number of items requested. As soon as the list capacity is exceeded, the least recent items are dropped.

We represent items as instances of RecommenderItem.java. Those instances provide access to data encoded in the JSON. When creating the RecommenderItem.java, the JSON is parsed and essential information such as item Id, publisher Id, and timestamp. The RecommenderItem.java instances are subsequently gathered in an array representation - RecommenderItemTable.java.

If you want to use this template to write your own recommender, you can use the item representations. Both Client.java and ContestHandler.java offer the opportunity to include a recommender. Those recommenders must return a List in order to create an adequate response. Note that you have to adjust the properties file to support the port used to communicate with the server. Further information can be found in http://orp.plista.com.

MIT License, (c) 2014, TU Berlin