Avro with MRUnit gives InstantiationException

问题

I'm using:

• hadoop-client 2.2.0
• mrunit 1.0.0
• avro 1.7.6
• avro-mrunit 1.7.6

... and the entire thing is being built and tested using Maven.

I was getting a NullPointerException until I followed the instructions at MRUnit with Avro NullPointerException in Serialization.

Now I am getting an InstantiationException:

Running mypackage.MyTest
log4j:WARN No appenders could be found for logger (org.apache.hadoop.metrics2.lib.MutableMetricsFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
2014-03-23 20:49:21.463 java[27994:1003] Unable to load realm info from SCDynamicStore
Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.945 sec <<< FAILURE!
process(mypackage.MyTest)  Time elapsed: 0.909 sec  <<< ERROR!
java.lang.RuntimeException: java.lang.InstantiationException
    at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:131)
    at org.apache.hadoop.io.serializer.SerializationFactory.add(SerializationFactory.java:72)
    at org.apache.hadoop.io.serializer.SerializationFactory.<init>(SerializationFactory.java:63)
    at org.apache.hadoop.mrunit.internal.io.Serialization.<init>(Serialization.java:37)
    at org.apache.hadoop.mrunit.TestDriver.getSerialization(TestDriver.java:464)
    at org.apache.hadoop.mrunit.TestDriver.copy(TestDriver.java:608)
    at org.apache.hadoop.mrunit.TestDriver.copyPair(TestDriver.java:612)
    at org.apache.hadoop.mrunit.MapDriverBase.addInput(MapDriverBase.java:118)
    at org.apache.hadoop.mrunit.MapDriverBase.withInput(MapDriverBase.java:207)
    at mypackage.MyTest.process(MyTest.java:92)
...

The Avro model looks like this:

{
    "namespace": "model",
    "type": "record",
    "name": "Blob",
    "fields": [
        { "name": "value", "type": "string" }
    ]
}

The mapper looks like this:

public class MyMapper
    extends Mapper<AvroKey<Blob>, NullWritable, LongWritable, NullWritable>
{
    @Override
    public void map(AvroKey<Blob> key, NullWritable value, Context context)
            throws IOException, InterruptedException {
        context.write(new LongWritable(0), NullWritable.get());
    }
}

The test that is failing (the only test I have at the moment) looks like this:

@Test
public void process() throws IOException {
    mapper = new MyMapper();
    job = Job.getInstance();
    mapDriver = MapDriver.newMapDriver(mapper);

    Configuration configuration = mapDriver.getConfiguration();
    //Copy over the default io.serializations. If you don't do this then you will 
    //not be able to deserialize the inputs to the mapper
    String[] serializations = configuration.getStrings("io.serializations");
    serializations = Arrays.copyOf(serializations, serializations.length + 1);
    serializations[serializations.length-1] = AvroSerialization.class.getName();
    configuration.setStrings("io.serializations", serializations);

    //Configure AvroSerialization by specifying the key writer and value writer schemas
    configuration.setStrings("avro.serialization.key.writer.schema", Schema.create(Schema.Type.LONG).toString(true));
    configuration.setStrings("avro.serialization.value.writer.schema", Schema.create(Schema.Type.NULL).toString(true));

    job.setMapperClass(MyMapper.class);
    job.setInputFormatClass(AvroKeyInputFormat.class);
    AvroJob.setInputKeySchema(job, Blob.SCHEMA$);
    job.setOutputKeyClass(LongWritable.class);

    input = Blob.newBuilder()
        .setValue("abc")
        .build();
    mapDriver
        .withInput(new AvroKey<Blob>(input), NullWritable.get())
        .withOutput(new LongWritable(0), NullWritable.get())
        .runTest();
}

I'm pretty new with both Avro and MRUnit, so I am still trying to fully understanding the workings between them. In the unit test output I see warnings about log4j and don't know for certain that this isn't part of the problem (thought I doubt it).

回答1:

Try this one; though It is error from ReflectionUtil but the outer frame is about Serialization and you do not implement your writable. So I think it may be about avro serializaion is not set right.

        MapDriver driver = MapDriver.newMapDriver(your mapper);

        Configuration conf = driver.getConfiguration();
        AvroSerialization.addToConfiguration(conf);
        AvroSerialization.setKeyWriterSchema(conf, your schema);
        AvroSerialization.setKeyReaderSchema(conf, your schema);
        Job job = new Job(conf);
        job.set... your job settings;
        AvroJob.set... your avro job settings;

来源：https://stackoverflow.com/questions/22591342/avro-with-mrunit-gives-instantiationexception