FixedSchemaKafkaAvroExtractor.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 gobblin.source.extractor.extract.kafka;

import org.apache.avro.Schema;
import org.apache.avro.io.Decoder;
import org.apache.avro.io.DecoderFactory;

import com.google.common.base.Preconditions;

import gobblin.annotation.Alias;
import gobblin.configuration.WorkUnitState;


/**
 * Extract avro records from a Kafka topic using a fixed schema provided by {@link #STATIC_SCHEMA_ROOT_KEY}.
 */
@Alias(value = "AVRO_FIXED_SCHEMA")
public class FixedSchemaKafkaAvroExtractor extends KafkaAvroExtractor<Void> {

  public static final String STATIC_SCHEMA_ROOT_KEY = "gobblin.source.kafka.fixedSchema";

  public FixedSchemaKafkaAvroExtractor(WorkUnitState state) {
    super(state);
  }

  @Override
  protected Schema getLatestSchemaByTopic(String topic) {
    String key = STATIC_SCHEMA_ROOT_KEY + "." + topic;
    Preconditions.checkArgument(this.workUnitState.contains(key),
        String.format("Could not find schema for topic %s. Looking for key %s.", topic, key));
    return new Schema.Parser().parse(this.workUnitState.getProp(key));
  }

  @Override
  protected Schema getRecordSchema(byte[] payload) {
    if (!this.schema.isPresent()) {
      throw new RuntimeException("Schema is not preset. This is an error in the code.");
    }
    return this.schema.get();
  }

  @Override
  protected Decoder getDecoder(byte[] payload) {
    return DecoderFactory.get().binaryDecoder(payload, null);
  }
}