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https://issues.apache.org/jira/browse/FLINK-17320?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17089417#comment-17089417
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Jingsong Lee commented on FLINK-17320:
--------------------------------------
Looks like the problem is: Comparator is not serializable. If the interface is
serializable, lambda expression can be serializable.
About this NPE, maybe it is a bug of kryo, but yes, we can improve kryo with
lambda.
> Java8 lambda expression cannot be serialized.
> ---------------------------------------------
>
> Key: FLINK-17320
> URL: https://issues.apache.org/jira/browse/FLINK-17320
> Project: Flink
> Issue Type: Bug
> Components: API / Type Serialization System, Table SQL / Runtime
> Affects Versions: 1.9.0
> Reporter: Jiayi Liao
> Priority: Major
>
> It happens when we want to use {{java.util.PriorityQueue}} in customed UDAF.
> The serialization error occurs with codes below.
> {code:java}
> @Test
> public void test() throws IOException {
> PriorityQueue<String> pq = new PriorityQueue<>((o1, o2) -> o1.length
> - o2.length - 1);
> pq.add("1234135");
> pq.add("12323424135");
> KryoSerializer kryoSerializer = new
> KryoSerializer(PriorityQueue.class, new ExecutionConfig());
> kryoSerializer.serialize(pq, new DataOutputSerializer(10240));
> }
> {code}
> And the NPE will be thrown:
> {code:java}
> Caused by: java.lang.NullPointerException
> at
> com.esotericsoftware.kryo.util.DefaultClassResolver.writeClass(DefaultClassResolver.java:80)
> at com.esotericsoftware.kryo.Kryo.writeClass(Kryo.java:488)
> at com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:593)
> at
> org.apache.flink.runtime.types.PriorityQueueSerializer.write(PriorityQueueSerializer.java:67)
> at
> org.apache.flink.runtime.types.PriorityQueueSerializer.write(PriorityQueueSerializer.java:40)
> at com.esotericsoftware.kryo.Kryo.writeClassAndObject(Kryo.java:599)
> at
> org.apache.flink.api.java.typeutils.runtime.kryo.KryoSerializer.serialize(KryoSerializer.java:307)
> at
> org.apache.flink.util.InstantiationUtil.serializeToByteArray(InstantiationUtil.java:526)
> {code}
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