Flink DataStream map Object 到对象列表

Question

I'm trying to convert a DataStream of an object A to list of Object B. As shown in the example below, I am reading DataStream from flink consumer and I need to convert to DataStream so I can run some filters and aggregations over timeWindow on MappedMetric objects. One single LogEvent may result in list of MappedMetric object so if I use MapFunction, result would be DataStream<List>. However, I think that aggregation can't be run on DataStream<List>. Any help is highly appreciated. Thanks in advance.

// Input Object
public class LogEvent {
    private String id;
    private long timestamp;
    private List<LogMessage> message;
}

public class LogMessage {
    private String accountId;
    private List<Metric> metrics;
}

public class Metric {
    private String name;
    private double value;
}

// Should be transformed to 

public class MappedMetric {
    private String accountId;
    private String name;
    private double value;
    private long timestamp;
}

final DataStream<LogEvent> inputDataStream = **read from Flink consumer**
final DataStream<MappedMetric> aggregatedMetrics = inputDataStream
                .map(**SomeMapFunction**)
                .keyBy(**SomeKey**)
                
                
                

Answer 1

You want to use a FlatMap function, which can generate multiple results for a single input. Each result is a single MappedMetric record, not a list.