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https://issues.apache.org/jira/browse/SPARK-19656?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15896194#comment-15896194
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Eric Maynard commented on SPARK-19656:
--------------------------------------
Here is a complete working example in Java:
{code:title=AvroTest.java|borderStyle=solid}
import org.apache.spark.sql.Row;
import org.apache.spark.sql.SparkSession;
import java.util.ArrayList;
public class AvroTest {
public static void main(String[] args){
//build spark session:
System.setProperty("hadoop.home.dir", "C:\\Hadoop");//windows hack
SparkSession spark =
SparkSession.builder().master("local").appName("Avro Test")
.config("spark.sql.warehouse.dir",
"file:///c:/tmp/spark-warehouse")//another windows hack
.getOrCreate();
//create data:
ArrayList list = new ArrayList<CustomClass>();
CustomClass cc = new CustomClass();
cc.setValue(5);
list.add(cc);
spark.createDataFrame(list,
CustomClass.class).write().format("com.databricks.spark.avro").save("C:\\tmp\\file.avro");
//read data:
Row row =
(spark.read().format("com.databricks.spark.avro").load("C:\\tmp\\file.avro").head());
System.out.println("Success =\t" + ((Integer)row.get(0) == 5));
}
}
{code}
With a simple custom class:
{code:title=CustomClass.java|borderStyle=solid}
import java.io.Serializable;
public class CustomClass implements Serializable {
public int value;
public void setValue(int value){this.value = value;}
public int getValue(){return this.value;}
}
{code}
Everything looks ok to me, and the main function prints "Success = true". In
the future please make sure that you don't have an issue in your application
before opening a JIRA. Also, as an aside, I really recommend picking up some
Scala as IMO the Scala API is much friendlier, esp. around the edges for things
like the avro library.
> 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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