flink-formats/flink-avro/src/main/java/org/apache/flink/formats/avro/AvroDeserializationSchema.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.formats.avro;

import org.apache.flink.api.common.serialization.DeserializationSchema;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.formats.avro.typeutils.AvroTypeInfo;
import org.apache.flink.formats.avro.typeutils.GenericRecordAvroTypeInfo;
import org.apache.flink.formats.avro.utils.MutableByteArrayInputStream;
import org.apache.flink.util.Preconditions;

import org.apache.avro.Schema;
import org.apache.avro.generic.GenericData;
import org.apache.avro.generic.GenericDatumReader;
import org.apache.avro.generic.GenericRecord;
import org.apache.avro.io.Decoder;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.specific.SpecificData;
import org.apache.avro.specific.SpecificDatumReader;
import org.apache.avro.specific.SpecificRecord;

import javax.annotation.Nullable;

import java.io.IOException;

/**
 * Deserialization schema that deserializes from Avro binary format.
 *
 * @param <T> type of record it produces
 */
public class AvroDeserializationSchema<T> implements DeserializationSchema<T> {

	/**
	 * Creates {@link AvroDeserializationSchema} that produces {@link GenericRecord} using provided schema.
	 *
	 * @param schema schema of produced records
	 * @return deserialized record in form of {@link GenericRecord}
	 */
	public static AvroDeserializationSchema<GenericRecord> forGeneric(Schema schema) {
		return new AvroDeserializationSchema<>(GenericRecord.class, schema);
	}

	/**
	 * Creates {@link AvroDeserializationSchema} that produces classes that were generated from avro schema.
	 *
	 * @param tClass class of record to be produced
	 * @return deserialized record
	 */
	public static <T extends SpecificRecord> AvroDeserializationSchema<T> forSpecific(Class<T> tClass) {
		return new AvroDeserializationSchema<>(tClass, null);
	}

	private static final long serialVersionUID = -6766681879020862312L;

	/** Class to deserialize to. */
	private final Class<T> recordClazz;

	/** Schema in case of GenericRecord for serialization purpose. */
	private final String schemaString;

	/** Reader that deserializes byte array into a record. */
	private transient GenericDatumReader<T> datumReader;

	/** Input stream to read message from. */
	private transient MutableByteArrayInputStream inputStream;

	/** Avro decoder that decodes binary data. */
	private transient Decoder decoder;

	/** Avro schema for the reader. */
	private transient Schema reader;

	/**
	 * Creates a Avro deserialization schema.
	 *
	 * @param recordClazz class to which deserialize. Should be one of:
	 *                    {@link SpecificRecord},
	 *                    {@link GenericRecord}.
	 * @param reader      reader's Avro schema. Should be provided if recordClazz is
	 *                    {@link GenericRecord}
	 */
	AvroDeserializationSchema(Class<T> recordClazz, @Nullable Schema reader) {
		Preconditions.checkNotNull(recordClazz, "Avro record class must not be null.");
		this.recordClazz = recordClazz;
		this.reader = reader;
		if (reader != null) {
			this.schemaString = reader.toString();
		} else {
			this.schemaString = null;
		}
	}

	GenericDatumReader<T> getDatumReader() {
		return datumReader;
	}

	Schema getReaderSchema() {
		return reader;
	}

	MutableByteArrayInputStream getInputStream() {
		return inputStream;
	}

	Decoder getDecoder() {
		return decoder;
	}

	@Override
	public T deserialize(byte[] message) throws IOException {
		// read record
		checkAvroInitialized();
		inputStream.setBuffer(message);
		Schema readerSchema = getReaderSchema();
		GenericDatumReader<T> datumReader = getDatumReader();

		datumReader.setSchema(readerSchema);

		return datumReader.read(null, decoder);
	}

	void checkAvroInitialized() {
		if (datumReader != null) {
			return;
		}

		ClassLoader cl = Thread.currentThread().getContextClassLoader();
		if (SpecificRecord.class.isAssignableFrom(recordClazz)) {
			SpecificData specificData = new SpecificData(cl);
			this.datumReader = new SpecificDatumReader<>(specificData);
			this.reader = specificData.getSchema(recordClazz);
		} else {
			this.reader = new Schema.Parser().parse(schemaString);
			GenericData genericData = new GenericData(cl);
			this.datumReader = new GenericDatumReader<>(null, this.reader, genericData);
		}

		this.inputStream = new MutableByteArrayInputStream();
		this.decoder = DecoderFactory.get().binaryDecoder(inputStream, null);
	}

	@Override
	public boolean isEndOfStream(T nextElement) {
		return false;
	}

	@Override
	@SuppressWarnings("unchecked")
	public TypeInformation<T> getProducedType() {
		if (SpecificRecord.class.isAssignableFrom(recordClazz)) {
			return new AvroTypeInfo(recordClazz, false);
		} else {
			return (TypeInformation<T>) new GenericRecordAvroTypeInfo(this.reader);
		}
	}
}