public String getYearKey() {
		return yearKey;
	}
Utility class used to generate keys for a named Aggregate Counter.
<ol>
The general format is </li>
<li>One total value</li>
<li>One years hash with a field per year eg. { 2010: value, 2011: value }</li>
<li>One hash per year with a field per month { 01: value, ...}</li>
<li>One hash per month with a field per day</li>
<li>One hash per day with a field per hour</li>
<li>One hash per hour with a field per minute</li>
</ol>

@author Mark Pollack
@author Luke Taylor
spring-xd-analytics/src/main/java/org/springframework/xd/analytics/metrics/redis/AggregateKeyGenerator.java