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https://issues.apache.org/jira/browse/SPARK-19656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15896166#comment-15896166
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Nira Amit commented on SPARK-19656:
-----------------------------------
[~emaynard] There is no "asInstanceOf" method in the Java API. And if I try to
cast it directly I get a compilation error.
[~sowen] Are you not handling tickets about the Java API? It's the second time
you close a ticket I open about loading custom objects from Avro in Java and
mark it as "Not a problem". Either this is not possible in Java, in which case
it's at least a missing feature (and misleading, because it looks like it
should be possible), or I'm not doing it right and in this case you can provide
a working code example in Java.
> Can't load custom type from avro file to RDD with newAPIHadoopFile
> ------------------------------------------------------------------
>
> Key: SPARK-19656
> URL: https://issues.apache.org/jira/browse/SPARK-19656
> Project: Spark
> Issue Type: Question
> Components: Java API
> Affects Versions: 2.0.2
> Reporter: Nira Amit
>
> If I understand correctly, in scala it's possible to load custom objects from
> avro files to RDDs this way:
> {code}
> ctx.hadoopFile("/path/to/the/avro/file.avro",
> classOf[AvroInputFormat[MyClassInAvroFile]],
> classOf[AvroWrapper[MyClassInAvroFile]],
> classOf[NullWritable])
> {code}
> I'm not a scala developer, so I tried to "translate" this to java as best I
> could. I created classes that extend AvroKey and FileInputFormat:
> {code}
> public static class MyCustomAvroKey extends AvroKey<MyCustomClass>{};
> public static class MyCustomAvroReader extends
> AvroRecordReaderBase<MyCustomAvroKey, NullWritable, MyCustomClass> {
> // with my custom schema and all the required methods...
> }
> public static class MyCustomInputFormat extends
> FileInputFormat<MyCustomAvroKey, NullWritable>{
> @Override
> public RecordReader<MyCustomAvroKey, NullWritable>
> createRecordReader(InputSplit inputSplit, TaskAttemptContext
> taskAttemptContext) throws IOException, InterruptedException {
> return new MyCustomAvroReader();
> }
> }
> ...
> JavaPairRDD<MyCustomAvroKey, NullWritable> records =
> sc.newAPIHadoopFile("file:/path/to/datafile.avro",
> MyCustomInputFormat.class, MyCustomAvroKey.class,
> NullWritable.class,
> sc.hadoopConfiguration());
> MyCustomClass first = records.first()._1.datum();
> System.out.println("Got a result, some custom field: " +
> first.getSomeCustomField());
> {code}
> This compiles fine, but using a debugger I can see that `first._1.datum()`
> actually returns a `GenericData$Record` in runtime, not a `MyCustomClass`
> instance.
> And indeed, when the following line executes:
> {code}
> MyCustomClass first = records.first()._1.datum();
> {code}
> I get an exception:
> {code}
> java.lang.ClassCastException: org.apache.avro.generic.GenericData$Record
> cannot be cast to my.package.containing.MyCustomClass
> {code}
> Am I doing it wrong? Or is this not possible in Java?
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