SplitReaderAdapter.java

/*
 * Copyright © 2014 Cask Data, Inc.
 *
 * Licensed 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 co.cask.cdap.api.data.batch;


/**
 * Handy adaptor for {@link SplitReader} to convert types.
 * @param <FROM_KEY>
 * @param <TO_KEY>
 * @param <FROM_VALUE>
 * @param <TO_VALUE>
 */
public abstract class SplitReaderAdapter<FROM_KEY, TO_KEY, FROM_VALUE, TO_VALUE> extends SplitReader<TO_KEY, TO_VALUE> {
  private final SplitReader<FROM_KEY, FROM_VALUE> delegate;

  public SplitReaderAdapter(SplitReader<FROM_KEY, FROM_VALUE> delegate) {
    this.delegate = delegate;
  }

  protected abstract TO_KEY convertKey(FROM_KEY key);
  protected abstract TO_VALUE convertValue(FROM_VALUE value);

  private TO_KEY nextKey = null;
  private TO_VALUE nextValue = null;

  @Override
  public void initialize(Split split) throws InterruptedException {
    delegate.initialize(split);
    nextKey = null;
    nextValue = null;
  }

  @Override
  public boolean nextKeyValue() throws InterruptedException {
    boolean hasNext = delegate.nextKeyValue();
    if (hasNext) {
      nextKey = convertKey(delegate.getCurrentKey());
      nextValue = convertValue(delegate.getCurrentValue());
    }
    return hasNext;
  }

  @Override
  public TO_KEY getCurrentKey() throws InterruptedException {
    return nextKey;
  }

  @Override
  public TO_VALUE getCurrentValue() throws InterruptedException {
    return nextValue;
  }

  @Override
  public void close() {
    delegate.close();
    nextKey = null;
    nextValue = null;
  }
}