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https://issues.apache.org/jira/browse/SPARK-19424?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15848981#comment-15848981
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Nira Amit edited comment on SPARK-19424 at 2/1/17 11:04 PM:
------------------------------------------------------------
[~srowen] thanks for elaborating, but in that case I just can't find a way to
do this in java other than loading GenericData.Record and converting it to my
class after loading. From what I've googled it appears that it's possible to do
this in scala this way:
{code}
ctx.hadoopFile("/path/to/the/avro/file.avro",
classOf[AvroInputFormat[MyClassInAvroFile]],
classOf[AvroWrapper[MyClassInAvroFile]],
classOf[NullWritable])
{code}
So I tried to "translate" this to java as best I could (hence the funky way for
getting the Class), but nothing works. I also tried with 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());
Tuple2<MyCustomAvroKey, NullWritable> first = records.first();
System.out.println("Got a result, id: " + first._1.datum().getSomeField()
{code}
But again the class inside MyCustomAvroKey is a GenericData.Record and not
MyCustomClass:
{code}
java.lang.ClassCastException: org.apache.avro.generic.GenericData$Record
cannot be cast to my.package.containing.MyCustomClass
{code}
Am I still doing it wrong? Or is this just not possible in java?
was (Author: amitnira):
[~srowen] thanks for elaborating, but in that case I just can't find a way to
do this in java other than loading GenericData.Record and converting it to my
class after loading. From what I've googled it appears that it's possible to do
this in scala this way:
{code}
ctx.hadoopFile("/path/to/the/avro/file.avro",
classOf[AvroInputFormat[MyClassInAvroFile]],
classOf[AvroWrapper[MyClassInAvroFile]],
classOf[NullWritable])
{code}
So I tried to "translate" this to java as best I could (hence the funky way for
getting the Class), but nothing works. I also tried with classes that extend
AvroKey and FileInputFormat:
{code}
public static class MyCustomAvroKey extends AvroKey<MyCustomClass>{};
public static class MyCustomAvroReader extends
AvroRecordReaderBase<MyCustomAvroKey, NullWritable, MyCustomClass> {
// with my custom schema and all the required methods...
}
public static class MyCustomInputFormat extends
FileInputFormat<MyCustomAvroKey, NullWritable>{
@Override
public RecordReader<MyCustomAvroKey, NullWritable>
createRecordReader(InputSplit inputSplit, TaskAttemptContext
taskAttemptContext) throws IOException, InterruptedException {
return new MyCustomAvroReader();
}
}
...
JavaPairRDD<MyCustomAvroKey, NullWritable> records =
sc.newAPIHadoopFile("file:/path/to/datafile.avro",
MyCustomInputFormat.class, MyCustomAvroKey.class,
NullWritable.class,
sc.hadoopConfiguration());
Tuple2<MyCustomAvroKey, NullWritable> first = records.first();
System.out.println("Got a result, id: " + first._1.datum().getSomeField()
{code}
But again the class inside MyCustomAvroKey is a GenericData.Record and not
MyCustomClass:
{code}
java.lang.ClassCastException: org.apache.avro.generic.GenericData$Record
cannot be cast to my.package.containing.MyCustomClass
{code}
Am I still doing it wrong? Or is this just not possible in java?
> Wrong runtime type in RDD when reading from avro with custom serializer
> -----------------------------------------------------------------------
>
> Key: SPARK-19424
> URL: https://issues.apache.org/jira/browse/SPARK-19424
> Project: Spark
> Issue Type: Bug
> Components: Java API
> Affects Versions: 2.0.2
> Environment: Ubuntu, spark 2.0.2 prebuilt for hadoop 2.7
> Reporter: Nira Amit
>
> I am trying to read data from avro files into an RDD using Kryo. My code
> compiles fine, but in runtime I'm getting a ClassCastException. Here is what
> my code does:
> {code}
> SparkConf conf = new SparkConf()...
> conf.set("spark.serializer", KryoSerializer.class.getCanonicalName());
> conf.set("spark.kryo.registrator", MyKryoRegistrator.class.getName());
> JavaSparkContext sc = new JavaSparkContext(conf);
> {code}
> Where MyKryoRegistrator registers a Serializer for MyCustomClass:
> {code}
> public void registerClasses(Kryo kryo) {
> kryo.register(MyCustomClass.class, new MyCustomClassSerializer());
> }
> {code}
> Then, I read my datafile:
> {code}
> JavaPairRDD<MyCustomClass, NullWritable> records =
> sc.newAPIHadoopFile("file:/path/to/datafile.avro",
> AvroKeyInputFormat.class, MyCustomClass.class,
> NullWritable.class,
> sc.hadoopConfiguration());
> Tuple2<MyCustomClass, NullWritable> first = records.first();
> {code}
> This seems to work fine, but using a debugger I can see that while the RDD
> has a kClassTag of my.package.containing.MyCustomClass, the variable first
> contains a Tuple2<AvroKey, NullWritable>, not Tuple2<MyCustomClass,
> NullWritable>! And indeed, when the following line executes:
> {code}
> System.out.println("Got a result, custom field is: " +
> first._1.getSomeCustomField());
> {code}
> I get an exception:
> {code}
> java.lang.ClassCastException: org.apache.avro.mapred.AvroKey cannot be cast
> to my.package.containing.MyCustomClass
> {code}
> Am I doing something wrong? And even so, shouldn't I get a compilation error
> rather than a runtime error?
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