NullPointerException when creating SpecificDatumWriter<T>

Question

While learning Apache Avro by Tom White's book, Hadoop: The Definitive Guide, I got an error.

The example has 3 steps:

1. Create an Avro schema file (Pair.avsc)

   {
      "type":"record",
      "name":"Pair",
      "doc":"A pair of strings.",
      "fields":[
         { "name":"left", "type":"string" },
         { "name":"right", "type":"string" }
      ]
   }
   

2. Compile the schema file to create a Java class (Pair.java) using

   $ java -jar $AVRO_HOME/avro-tools-1.6.2.jar compile schema src/main/resources/Pair.avsc src/main/java/

3. Use SpecificDatumWriter<Pair> and SpecificDatumReader<Pair> to serialize/deserialize data.

The original example method is testPairSpecific() in https://github.com/tomwhite/hadoop-book/blob/master/avro/src/main/java/AvroTest.java .

I rewrote the example code (createPairAndSerializeThenDeserialize() in https://github.com/philipjkim/avro-examples/blob/master/src/test/java/org/sooo/AvroTest.java), which is almost similar to the original one. The differneces are:

1. Avro version I used is 1.6.2, in original 1.3.2.
2. The contents of Pair.java created by avro-tools.jar differ (original: https://github.com/tomwhite/hadoop-book/blob/master/avro/src/main/java/Pair.java , mine: https://github.com/philipjkim/avro-examples/blob/master/src/main/java/org/sooo/Pair.java )

After running the test, I got an error:

java.lang.NullPointerException
at java.lang.String.replace(String.java:2228)
at org.apache.avro.specific.SpecificData.createSchema(SpecificData.java:195)
at org.apache.avro.specific.SpecificData.getSchema(SpecificData.java:140)
at org.apache.avro.specific.SpecificDatumWriter.<init>(SpecificDatumWriter.java:33)
at org.sooo.AvroTest.createPairAndSerializeThenDeserialize(AvroTest.java:86)
    ...

AvroTest.createPairAndSerializeThenDeserialize() is:

@Test
public void createPairAndSerializeThenDeserialize() throws IOException {
    // given
    Pair datum = new Pair();
    datum.setLeft(new Utf8("L"));
    datum.setRight(new Utf8("R"));

    // serialize
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    DatumWriter<Pair> writer = new SpecificDatumWriter<Pair>(Pair.class); /* Line 86 */
    Encoder encoder = EncoderFactory.get().binaryEncoder(out, null);
    writer.write(datum, encoder);
    encoder.flush();
    out.close();

    // deserialize
    DatumReader<Pair> reader = new SpecificDatumReader<Pair>(Pair.class);
    Decoder decoder = DecoderFactory.get().binaryDecoder(out.toByteArray(),
    null);
    Pair result = reader.read(null, decoder);

    // then
    assertThat(result.getLeft().toString(), is("L"));
    assertThat(result.getRight().toString(), is("R"));
}

I'd like to know what is wrong with this example. Thanks for any comments.

FYI, my example project repo is https://github.com/philipjkim/avro-examples .

Answer 1

Your Pair.avsc file is missing a namespace field for your custom package name:

...
  "namespace": "org.sooo",
...