[jira] [Created] (FLINK-6423) JoinFunction can not be replaced with lambda

["Moshe Sayag (JIRA)" <ji...@apache.org>]

Moshe Sayag created FLINK-6423:
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             Summary: JoinFunction can not be replaced with lambda
                 Key: FLINK-6423
                 URL: https://issues.apache.org/jira/browse/FLINK-6423
             Project: Flink
          Issue Type: Bug
          Components: DataStream API
    Affects Versions: 1.2.0
            Reporter: Moshe Sayag
            Priority: Minor


JoinedStreams.WithWindow.apply(...) can get a JoinFunction as a parameter, but not an equivalent lambda.

Consider the following code, runWithFunction completes successfully, while runWithLambda throws "java.lang.ArrayIndexOutOfBoundsException: -1"

As this might look like a very minor issue, the exception is not clear and might cause a developer to spend precious time while looking for the cause

    public void runWithFunction() throws Exception {
        StreamExecutionEnvironment env = LocalStreamEnvironment.getExecutionEnvironment();
        env.setStreamTimeCharacteristic(TimeCharacteristic.ProcessingTime);

        DataStream<String> stream1 = env.fromElements("a", "b", "c");
        DataStream<String> stream2 = env.fromElements("A", "B", "C");

        DataStream<String> joined = stream1.join(stream2)
                .where(String::toLowerCase).equalTo(String::toLowerCase)
                .window(ProcessingTimeSessionWindows.withGap(Time.minutes(1)))
                .apply(new JoinFunction<String, String, String>() {
                    @Override
                    public String join(String s1, String s2) {
                        return s1 + "_" + s2;
                    }
                });
        joined.print();

        env.execute();
    }

    public void runWithLambda() throws Exception {
        StreamExecutionEnvironment env = LocalStreamEnvironment.getExecutionEnvironment();
        env.setStreamTimeCharacteristic(TimeCharacteristic.ProcessingTime);

        DataStream<String> stream1 = env.fromElements("a", "b", "c");
        DataStream<String> stream2 = env.fromElements("A", "B", "C");

        DataStream<String> joined = stream1.join(stream2)
                .where(String::toLowerCase).equalTo(String::toLowerCase)
                .window(ProcessingTimeSessionWindows.withGap(Time.minutes(1)))
                .apply((JoinFunction<String, String, String>) (s1, s2) -> s1 + "_" + s2);
        joined.print();

        env.execute();
    }



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