我是Apache Beam的初学者。我没有实现聚合的逻辑的问题，因为无法在自定义类中使用抽象类型而感到恼火。
我有一些自定义类，它们用作PTransforms的输入/输出。在这些类中，我想使用抽象类型，例如Set<String>而不是HashSet<String>，但我不能，至少使用AvroCoder。是否还有其他方法可以指定自动支持这些类型的类的编码器，还是我需要指定自己的编码器。
示例类：
@DefaultCoder(AvroCoder.class)
public class WordStatistics {
public String key;
public Set<String> displays;
}
使用Set代替HashSet的异常
Caused by: java.lang.NoSuchMethodException: java.util.Set.<init>()
at java.lang.Class.getConstructor0(Class.java:3082)
at java.lang.Class.getDeclaredConstructor(Class.java:2178)
at org.apache.avro.specific.SpecificData.newInstance(SpecificData.java:347)
at org.apache.avro.reflect.ReflectDatumReader.newArray(ReflectDatumReader.java:100)
at org.apache.avro.reflect.ReflectDatumReader.readArray(ReflectDatumReader.java:133)
at org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:177)
at org.apache.avro.reflect.ReflectDatumReader.readField(ReflectDatumReader.java:302)
at org.apache.avro.generic.GenericDatumReader.readRecord(GenericDatumReader.java:222)
at org.apache.avro.generic.GenericDatumReader.readWithoutConversion(GenericDatumReader.java:175)
at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:153)
at org.apache.avro.generic.GenericDatumReader.read(GenericDatumReader.java:145)
at org.apache.beam.sdk.coders.AvroCoder.decode(AvroCoder.java:317)
at org.apache.beam.sdk.coders.Coder.decode(Coder.java:159)
at org.apache.beam.sdk.coders.KvCoder.decode(KvCoder.java:82)
at org.apache.beam.sdk.coders.KvCoder.decode(KvCoder.java:36)
at org.apache.beam.sdk.util.CoderUtils.decodeFromSafeStream(CoderUtils.java:115)
at org.apache.beam.sdk.util.CoderUtils.decodeFromByteArray(CoderUtils.java:98)
at org.apache.beam.sdk.util.CoderUtils.decodeFromByteArray(CoderUtils.java:92)
at org.apache.beam.sdk.util.CoderUtils.clone(CoderUtils.java:141)
at org.apache.beam.sdk.util.MutationDetectors$CodedValueMutationDetector.<init>(MutationDetectors.java:113)
at org.apache.beam.sdk.util.MutationDetectors.forValueWithCoder(MutationDetectors.java:44)
at org.apache.beam.runners.direct.ImmutabilityCheckingBundleFactory$ImmutabilityEnforcingBundle.add(ImmutabilityCheckingBundleFactory.java:112)
at org.apache.beam.runners.direct.ParDoEvaluator$BundleOutputManager.output(ParDoEvaluator.java:260)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimpleDoFnRunner.outputWindowedValue(SimpleDoFnRunner.java:309)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimpleDoFnRunner.access$700(SimpleDoFnRunner.java:77)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimpleDoFnRunner$DoFnProcessContext.output(SimpleDoFnRunner.java:621)
at org.apache.beam.sdk.transforms.DoFnOutputReceivers$WindowedContextOutputReceiver.output(DoFnOutputReceivers.java:71)
at com.unsilo.transforms.FromAccumulatorToStatsMapper.processElement(FromAccumulatorToStatsMapper.java:14)
at com.unsilo.transforms.FromAccumulatorToStatsMapper$DoFnInvoker.invokeProcessElement(Unknown Source)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimpleDoFnRunner.invokeProcessElement(SimpleDoFnRunner.java:275)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimpleDoFnRunner.processElement(SimpleDoFnRunner.java:240)
at org.apache.beam.repackaged.beam_runners_direct_java.runners.core.SimplePushbackSideInputDoFnRunner.processElementInReadyWindows(SimplePushbackSideInputDoFnRunner.java:78)
at org.apache.beam.runners.direct.ParDoEvaluator.processElement(ParDoEvaluator.java:207)
at org.apache.beam.runners.direct.DoFnLifecycleManagerRemovingTransformEvaluator.processElement(DoFnLifecycleManagerRemovingTransformEvaluator.java:55)
at org.apache.beam.runners.direct.DirectTransformExecutor.processElements(DirectTransformExecutor.java:160)
at org.apache.beam.runners.direct.DirectTransformExecutor.run(DirectTransformExecutor.java:124)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266)
at java.util.concurrent.FutureTask.run(FutureTask.java)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)