Database Reference
In-Depth Information
each(System.
currentTimeMillis
(),key,value,cmd);
}
}
The
Command<E>
interface, covered in the next section, contains a single
function that is used to implement operations in a client. The
Expirer
interface is similar and used by clients that can implement an optional
expiration feature.
NOTE
The aggregation driver assumes that messages are delivered with a
timestamp. This allows for messages to be delivered out-of-order or
even with significant delay, but still be delivered to the correct “time
bucket” of the back-end store. It also implements a simpler version of
each
that simply uses the current time.
Implementing Clients
Implementing a client that uses the aggregation driver usually means
implementing a series of
Command<E>
interfaces as anonymous classes.
These are wrapped inside a method to implement a multi-resolution version
of the method. The following example prints the multi-resolution key and
value to the console:
public void
doSomething(
long
timestamp,String
key,String value) {
aggregator.each(timestamp, key, value,
new
Command<String>() {
public
String execute(
long
timestamp,
long
quantized,
String quantizedString, String key, String
value) {
String k = key+":"+quantizedString;
System.
out
.println(k+"="+value);
return
k;
}
