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https://issues.apache.org/jira/browse/FLINK-2495?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14661525#comment-14661525
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Fabian Hueske edited comment on FLINK-2495 at 8/7/15 9:00 AM:
--------------------------------------------------------------
[~Huangwei], you are right. I did't look close enough, sorry.
However, I don't think it is a good idea to silently ignore {{null}} inputs in
a {{union}}. First, a {{null}} input indicates a serious problem with the user
program that should be clearly indicated. Second, ignoring a {{null}} input is
possible for a {{union}} but not for other operators such as {{comap}} or
{{join}}. Hence ignoring the {{null}} input for {{union}} would lead to
inconsistent behavior of the API, in my opinion.
was (Author: fhueske):
[~Huangwei], you are right. I did't look close enough, sorry.
However, I don't think it is a good idea to silently ignore {{null}} inputs in
a {{union}}. First, a {{null}} input indicates a serious problem with the user
program that should be clearly indicated. Second, ignoring a {{null}} input is
possible for a {{union}} but not for a {{join}}, {{cogroup}}, {{cross}}, or
iteration. Hence ignoring the {{null}} input for {{union}} would lead to
inconsistent behavior of the API, in my opinion.
> Add a null point check in API DataStream.union
> ----------------------------------------------
>
> Key: FLINK-2495
> URL: https://issues.apache.org/jira/browse/FLINK-2495
> Project: Flink
> Issue Type: Bug
> Components: Streaming
> Affects Versions: 0.10
> Reporter: Huang Wei
> Fix For: 0.10
>
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> The API(public DataStream<OUT> union(DataStream<OUT>... streams)) is a
> external interface for user.
> The parameter "streams" maybe null and it will throw NullPointerException
> error.
> This test below can be intuitive to explain this problem:
> package org.apache.flink.streaming.api;
> import org.apache.flink.api.common.functions.MapFunction;
> import org.apache.flink.streaming.api.datastream.DataStream;
> import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
> import
> org.apache.flink.streaming.api.functions.source.RichParallelSourceFunction;
> import org.junit.Test;
> /**
> * Created by HuangWHWHW on 2015/8/7.
> */
> public class test {
> public static class sourceFunction extends
> RichParallelSourceFunction<String> {
> public sourceFunction() {
> }
> @Override
> public void run(SourceContext<String> sourceContext) throws
> Exception {
> sourceContext.collect("a");
> }
> @Override
> public void cancel() {
> }
> }
> @Test
> public void testUnion(){
> StreamExecutionEnvironment env =
> StreamExecutionEnvironment.getExecutionEnvironment();
> env.setParallelism(1);
> DataStream<String> source = env.addSource(new sourceFunction());
> DataStream<String> temp1 = null;
> DataStream<String> temp2 = source.map(new MapFunction<String,
> String>() {
> @Override
> public String map(String value) throws Exception {
> if (value == "a") {
> return "This is for test temp2.";
> }
> return null;
> }
> });
> DataStream<String> sink = temp2.union(temp1);
> sink.print();
> try {
> env.execute();
> }catch (Exception e){
> e.printStackTrace();
> }
> }
> }
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