Summing a number from a random number source - apache-flink

Question

I'm just starting to learn flink and trying to build a very basic toy example which sums an integer over time and periodically prints the total sum so far
I've created a random number generator source class like this:
// RandomNumberSource.java
public class RandomNumberSource implements SourceFunction<Integer> {
public volatile boolean isRunning = true;
private Random rand;
public RandomNumberSource() {
this.rand = new Random();
}
#Override
public void run(SourceContext<Integer> ctx) throws Exception {
while (isRunning) {
ctx.collect(rand.nextInt(200));
Thread.sleep(1000L);
}
}
#Override
public void cancel() {
this.isRunning = false;
}
}
As you can see, it generates a random number every 1 second
Now how would I go about summing the number that's being generated?
// StreamJob.java
public class StreamingJob {
public static void main(String[] args) throws Exception {
// set up the streaming execution environment
final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Integer> randomNumber = env.addSource(new RandomNumberSource());
// pseudo code:
// randomNumber
// .window(Time.seconds(5))
// .reduce(0, (acc, i) => acc+i) // (initial value, reducer)
// .sum()
// execute program
env.execute("Flink Streaming Random Number Sum Aggregation");
}
}
I've added pseudo code to explain what I'm trying to do. i.e every 5 seconds, perform a sum of all the numbers and print it out.
I feel like I'm missing something in my approach and might need some guidance on how to do this.

Answer 1

window operator is used for keyed streams. You should instead use windowAll for this task. Here's the snippet:
randomNumber
.windowAll(TumblingProcessingTimeWindows.of(Time.seconds(5)))
.sum(0)
.print()
.setParallelism(1);
Also check this for reference on various window considerations.