David Anderson created FLINK-27456:
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Summary: mistake and confusion with CEP example in docs
Key: FLINK-27456
URL: https://issues.apache.org/jira/browse/FLINK-27456
Project: Flink
Issue Type: Bug
Components: Documentation, Library / CEP
Affects Versions: 1.14.4
Reporter: David Anderson
[https://nightlies.apache.org/flink/flink-docs-master/docs/libs/cep/#contiguity-within-looping-patterns]
In the section of the docs on contiguity within looping patterns, what it says
about strict contiguity for the given example is either incorrect or very
confusing (or both). It doesn't help that the example code doesn't precisely
match the scenario described in the text.
To study this, I implemented the example in the text and find it produces no
output for strict contiguity (as I expected), which contradicts what the text
says.
{code:java}
public class StreamingJob {
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env =
StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<String> events = env.fromElements("a", "b1", "d1", "b2",
"d2", "b3", "c");
AfterMatchSkipStrategy skipStrategy =
AfterMatchSkipStrategy.skipPastLastEvent();
Pattern<String, String> pattern =
Pattern.<String>begin("a", skipStrategy)
.where(
new SimpleCondition<String>() {
@Override
public boolean filter(String element)
throws Exception {
return element.startsWith("a");
}
})
.next("b+")
.where(
new SimpleCondition<String>() {
@Override
public boolean filter(String element)
throws Exception {
return element.startsWith("b");
}
})
.oneOrMore().consecutive()
.next("c")
.where(
new SimpleCondition<String>() {
@Override
public boolean filter(String element)
throws Exception {
return element.startsWith("c");
}
});
PatternStream<String> patternStream = CEP.pattern(events,
pattern).inProcessingTime();
patternStream.select(new SelectSegment()).addSink(new
PrintSinkFunction<>(true));
env.execute();
}
public static class SelectSegment implements PatternSelectFunction<String,
String> {
public String select(Map<String, List<String>> pattern) {
return String.join("", pattern.get("a"))
+ String.join("", pattern.get("b+"))
+ String.join("", pattern.get("c"));
}
}
}
{code}
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