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/*
 * Copyright 2012, 2020 International Business Machines Corp.
 *
 * See the NOTICE file distributed with this work for additional information
 * regarding copyright ownership. 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.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

package jakarta.batch.api.chunk;

import java.io.Serializable;
/**
 *
 * ItemReader defines the batch artifact that reads
 * items for chunk processing.
 *
 */
public interface ItemReader {

	/**
	 * The open method prepares the reader to read items.
	 *
	 * The input parameter represents the last checkpoint
	 * for this reader in a given job instance. The
	 * checkpoint data is defined by this reader and is
	 * provided by the checkpointInfo method. The checkpoint
	 * data provides the reader whatever information it needs
	 * to resume reading items upon restart. A checkpoint value
	 * of null is passed upon initial start.
	 *
	 * @param checkpoint specifies the last checkpoint
	 * @throws Exception is thrown for any errors.
	 */
	public void open(Serializable checkpoint) throws Exception;
	/**
	 * The close method marks the end of use of the
	 * ItemReader. The reader is free to do any cleanup
	 * necessary.
	 * @throws Exception is thrown for any errors.
	 */
	public void close() throws Exception;
	/**
	 * The readItem method returns the next item
	 * for chunk processing.
	 * It returns null to indicate no more items, which
	 * also means the current chunk will be committed and
	 * the step will end.
	 * @return next item or null
	 * @throws Exception is thrown for any errors.
	 */
	public Object readItem() throws Exception;
	/**
	 * The checkpointInfo method returns the current
	 * checkpoint data for this reader. It is
	 * called before a chunk checkpoint is committed.
	 * @return checkpoint data
	 * @throws Exception is thrown for any errors.
	 */
	public Serializable checkpointInfo() throws Exception;

}