Flink Complex Event Processing - apache-flink

Question

I have a flink cep code that reads from socket and detects for a pattern. Lets say the pattern(word) is 'alert'. If the word alert occurs five times or more, an alert should be created. But I am getting an input mismatch error. Flink version is 1.3.0. Thanks in advance !!
package pattern;
import org.apache.flink.cep.CEP;
import org.apache.flink.cep.PatternStream;
import org.apache.flink.cep.pattern.Pattern;
import org.apache.flink.cep.pattern.conditions.IterativeCondition;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.datastream.DataStreamSource;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.util.Collector;
import java.util.List;
import java.util.Map;
public class cep {
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStreamSource<String> dss = env.socketTextStream("localhost", 3005);
dss.print();
Pattern<String,String> pattern = Pattern.<String> begin("first")
.where(new IterativeCondition<String>() {
#Override
public boolean filter(String word, Context<String> context) throws Exception {
return word.equals("alert");
}
})
.times(5);
PatternStream<String> patternstream = CEP.pattern(dss, pattern);
DataStream<String> alerts = patternstream
.flatSelect((Map<String,List<String>> in, Collector<String> out) -> {
String first = in.get("first").get(0);
for (int i = 0; i < 6; i++ ) {
out.collect(first);
}
});
alerts.print();
env.execute();
}
}

Answer 1

Just some clarification on the original problem. In 1.3.0 there was a bug that made using lambdas as arguments to select/flatSelect impossible.
It was fixed in 1.3.1, so your first version of the code would work with 1.3.1.
Besides I think you misinterpret the times quantifier. It matches exact number of times. So in your case it will return only when event will be matched exactly 3 times, not 3 or more.

Answer 2

So I have got the code to work. Here is the working solution,
package pattern;
import org.apache.flink.cep.CEP;
import org.apache.flink.cep.PatternSelectFunction;
import org.apache.flink.cep.PatternStream;
import org.apache.flink.cep.pattern.Pattern;
import org.apache.flink.cep.pattern.conditions.IterativeCondition;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.datastream.DataStreamSource;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.util.Collector;
import java.util.List;
import java.util.Map;
public class cep {
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStreamSource<String> dss = env.socketTextStream("localhost", 3005);
dss.print();
Pattern<String,String> pattern = Pattern.<String> begin("first")
.where(new IterativeCondition<String>() {
#Override
public boolean filter(String word, Context<String> context) throws Exception {
return word.equals("alert");
}
})
.times(5);
PatternStream<String> patternstream = CEP.pattern(dss, pattern);
DataStream<String> alerts = patternstream
.select(new PatternSelectFunction<String, String>() {
#Override
public String select(Map<String, List<String>> in) throws Exception {
String first = in.get("first").get(0);
if(first.equals("alert")){
return ("5 or more alerts");
}
else{
return (" ");
}
}
});
alerts.print();
env.execute();
}
}