google-cloud-dataflow - 具有通用功能的 Google Cloud Dataflow 自定义键

Question

我们正在使用 Dataflow Java SDK，并且我们有越来越多的几乎相同的自定义键类。

我想让它们扩展一个通用的抽象类，但是 Dataflow SDK 似乎试图实例化导致 InstantiationException 的抽象类。

Caused by: java.lang.RuntimeException: java.lang.InstantiationException
    at org.apache.avro.specific.SpecificData.newInstance(SpecificData.java:316)
    at org.apache.avro.specific.SpecificData.newRecord(SpecificData.java:332)
    at org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:173)
    at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:151)
    at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:142)
    at com.google.cloud.dataflow.sdk.coders.AvroCoder.decode(AvroCoder.java:242)
    at com.google.cloud.dataflow.sdk.coders.KvCoder.decode(KvCoder.java:97)
    at com.google.cloud.dataflow.sdk.coders.KvCoder.decode(KvCoder.java:42)
    at com.google.cloud.dataflow.sdk.util.CoderUtils.decodeFromSafeStream(CoderUtils.java:156)
    at com.google.cloud.dataflow.sdk.util.CoderUtils.decodeFromByteArray(CoderUtils.java:139)
    at com.google.cloud.dataflow.sdk.util.CoderUtils.decodeFromByteArray(CoderUtils.java:133)
    at com.google.cloud.dataflow.sdk.util.MutationDetectors$CodedValueMutationDetector.<init>(MutationDetectors.java:108)
    at com.google.cloud.dataflow.sdk.util.MutationDetectors.forValueWithCoder(MutationDetectors.java:45)
    at com.google.cloud.dataflow.sdk.transforms.ParDo$ImmutabilityCheckingOutputManager.output(ParDo.java:1218)
    at com.google.cloud.dataflow.sdk.util.DoFnRunner$DoFnContext.outputWindowedValue(DoFnRunner.java:329)
    at com.google.cloud.dataflow.sdk.util.DoFnRunner$DoFnProcessContext.output(DoFnRunner.java:483)
    at com.telstra.cdf.rmr.model.pardos.ParDoAbstractCampaignUAKeyExtractor.processElement(ParDoAbstractCampaignUAKeyExtractor.java:5

这是我们的抽象类，

@DefaultCoder(AvroCoder.class)
public abstract class SuperClassKey  {
    public SuperClassKey(){}
    public abstract double getSomeValue();
}

这是子类

@DefaultCoder(AvroCoder.class)
public class SubClassKey extends SuperClassKey {
    public String foo;

    public SubClassKey() {
    }

    public SubClassKey(String foo){
        this.foo = foo;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        SubClassKey that = (SubClassKey) o;

        if (!foo.equals(that.foo)) return false;

        return true;
    }

    @Override
    public int hashCode() {
        return foo.hashCode();
    }

    @Override
    public double getSomeValue() {
        return foo;
    }
}

我也尝试过使用接口(interface)但没有成功。

Key之间是否可以有一个共同的抽象类或接口(interface)？

Answer 1

问题可能是由于使用了 PCollection<SuperClassKey>而不是 PCollection<SubClassKey> . PCollection 需要用一个具体的类来键入。可以使用 .setCoder(AvroCoder.of(SubClassKey.class)) 显式指定编码器如果类型推断是不够的。