why getSideOutput emit nothing? - apache-flink

Question

I using getSideOutput to create a side output stream, Presence of element in the pre-processing stream before processing with getSideOutput, but when calling getSideOutput method, nothing element is emitted.
code as follow
DataStream<String> asyncTable =
join3
.flatMap(new ExtractList())
.process( // detect code using for test
new ProcessFunction<String, String>() {
#Override
public void processElement(String value, Context ctx, Collector<String> out)
throws Exception {
System.out.println(value); // can detect elements
}
})
.getSideOutput(new OutputTag<>("asyTab", TypeInformation.of(String.class)));
but when calling getSideOutput method after
DataStream<String> asyncTable =
join3
.flatMap(new ExtractList())
.getSideOutput(new OutputTag<>("asyTab", TypeInformation.of(String.class)))
.process(
new ProcessFunction<String, String>() {
#Override
public void processElement(String value, Context ctx, Collector<String> out)
throws Exception {
System.out.println(value); // nothing detect elements
}
});
ExtractList as follows
import org.apache.flink.util.Collector;
public class ExtractList extends RichFlatMapFunction<NewTableA, String> {
#Override
public void flatMap(NewTableA value, Collector<String> out) throws Exception {
String tableName = "NewTableA";
String primaryKeyName = "PA1";
String primaryValue = value.getPA1().toString();
String result = tableName+":"+primaryKeyName+":"+primaryValue;
//System.out.println(result); // right result output
out.collect(result);
}
}
why getSideOutput to create a side output stream with nothing elements.

Answer 1

The same output tag id should be used - in your case, it's asyncTableValue in ExtractList and asyTab in .getSideOutput(new OutputTag<>("asyTab", TypeInformation.of(String.class))); which are definetely different and therefore asyTab side output emits nothing.

Answer 2

sorry, it is my mistake.
I don't code in ExtractList
public class ExtractList extends ProcessFunction<NewTableA, NewTableA> {
private OutputTag<String> asyncTableValue =
new OutputTag<String>("asyncTableValue", TypeInformation.of(String.class));
#Override
public void processElement(NewTableA value, Context ctx, Collector<NewTableA> out)
throws Exception {
String tableName = "NewTableA";
String primaryKeyName = "PA1";
String primaryValue = value.getPA1().toString();
String result = tableName + ":" + primaryKeyName + ":" + primaryValue;
ctx.output(asyncTableValue, result);
out.collect(value);
}
}