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Date: Wed, 22 Jun 2016 16:31:58 +0000 (UTC)
From: "Ryan Blue (JIRA)" <jira@apache.org>
To: dev@avro.apache.org
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Subject: [jira] [Commented] (AVRO-1865) GenericData.Array class missing no
 arg constructor for Kryo serialization
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archived-at: Wed, 22 Jun 2016 16:32:01 -0000


    [ https://issues.apache.org/jira/browse/AVRO-1865?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15344683#comment-15344683 ] 

Ryan Blue commented on AVRO-1865:
---------------------------------

The schema needs to be there, but for Kryo will be set during deserialization, not during construction. That's why we should have a comment on the schema-less constructor saying not to actually use it because it's for deserialization via Kryo or Java Serialization only.

> GenericData.Array class missing no arg constructor for Kryo serialization
> -------------------------------------------------------------------------
>
>                 Key: AVRO-1865
>                 URL: https://issues.apache.org/jira/browse/AVRO-1865
>             Project: Avro
>          Issue Type: Bug
>          Components: java
>    Affects Versions: 1.8.1
>            Reporter: Alexander Kasper
>              Labels: newbie, patch
>         Attachments: add-no-arg-ctor-genericdata-array.diff
>
>
> When trying to serialize Java classes generated by Avro that contain a field as follows:
> {{array<MyClass> myclasses = []}}
> serialization fails with the following error message
> {{com.esotericsoftware.kryo.KryoException: Class cannot be created (missing no-arg constructor)}}
> Minimum example to recreate this:
> Avro IDL definition:
> {code:java}
> @namespace("com.adello")
> protocol KryoTest {
> 	record TestRecord {
> 		array<int> values = [];
> 	}
> }
> {code}
> This gets compiled using {{java -jar avro-tools-1.8.1.jar idl2schemata kryo.avdl .}}
> Resulting Avro schema:
> {code:javascript}
> {
>   "type" : "record",
>   "name" : "TestRecord",
>   "namespace" : "com.adello",
>   "fields" : [ {
>     "name" : "values",
>     "type" : {
>       "type" : "array",
>       "items" : "int"
>     },
>     "default" : [ ]
>   } ]
> }
> {code}
> Generate Java class using {{java -jar avro-tools-1.8.1.jar compile schema TestRecord.avsc}}
> Kryo serialization test code:
> {code:java}
> Kryo kryo = new Kryo();
> try {
>             Output output = new Output(new FileOutputStream("test.bin"));
>             TestRecord o = TestRecord.newBuilder().build();
>             System.out.println("Before serialization: ");
>             System.out.println(o.toString());
>             kryo.writeObject(output, o);
>             output.close();
>             Input input = new Input(new FileInputStream("test.bin"));
>             TestRecord i = kryo.readObject(input, TestRecord.class);
>             input.close();
>             System.out.println("After deserialization: ");
>             System.out.println(i.toString());
>             System.out.println(Objects.deepEquals(o, i));
>         } catch (FileNotFoundException e) {
>             e.printStackTrace();
>         }
> {code}
> This is a common enough issue with Kryo that they have a dedicated section on their website on it: http://docs.datatorrent.com/troubleshooting/#application-throwing-following-kryo-exception
> The attached patch adds a no args constructor for the inner class Array of GenericData with zero entries and a dummy schema. My personal tests for serialization with Kryo were successful when using it. Since I do not have complete insight into Avro I'd like to know if this could be a breaking change and how to test it if so.



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