Exact Aggregation and Delivery - Real-Time Analytics - page 362

This section describes the implementation of the first feature as a generic
class that can be used in a variety of situations. It then implements the
second piece for the Redis key-value store discussed in Chapter 6, “Storing
Streaming Data.” Redis was chosen because it implements a variety of
operations as well as supporting expiration in a single back end.

Defining Aggregates

The core of the Aggregator class is the Aggregate class. This class
defines the resolution of the aggregate as well as its retention time. The
class itself is fairly simple, consisting mostly of convenience functions that
are in the complete source. The part presented here is the functional part
of the class. The first part of the class defines formatters for the various
aggregation resolutions. These formats are chosen over simple millisecond
times because they are a bit more readable without sacrificing the numerical
and lexicographical ordering:

public class Aggregate {
private static final SimpleDateFormat
millisecondFormatter
= new SimpleDateFormat("yyyyMMddHHmmssSSS");
private static final SimpleDateFormat secondFormatter
= new SimpleDateFormat("yyyyMMddHHmmss");
private static final SimpleDateFormat minuteFormatter
= new SimpleDateFormat("yyyyMMddHHmm");
private static final SimpleDateFormat hourFormatter
= new SimpleDateFormat("yyyyMMddHH");
private static final SimpleDateFormat dayFormatter
= new SimpleDateFormat("yyyyMMdd");
private static SimpleDateFormat formatForMillis( long
millis) {
if (millis < 1000)

return

millisecondFormatter ;
if (millis < 60*1000) return secondFormatter ;
if (millis < 3600*1000) return minuteFormatter ;
if (millis < 86400*1000) return hourFormatter ;
return dayFormatter ;

}