public void setDateFormat(String pattern) {
		Assert.hasText(pattern, "dateFormat pattern must not be empty");
		this.dateFormat = DateTimeFormat.forPattern(pattern);
	}
Handles incoming messages for the {@code aggregate-counter} module, resolves SpEL expressions
as needed and delegate the heavy lifting to an {@link AggregateCounterRepository}.

@author Luke Taylor
@author Eric Bottard
spring-xd-analytics/src/main/java/org/springframework/xd/analytics/metrics/integration/AggregateCounterHandler.java