spring-batch StepContextRepeatCallback 源码

spring-batch StepContextRepeatCallback 代码

文件路径：/spring-batch-core/src/main/java/org/springframework/batch/core/scope/context/StepContextRepeatCallback.java

/*
 * Copyright 2006-2018 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.batch.core.scope.context;

import java.util.Queue;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.batch.core.Step;
import org.springframework.batch.core.StepExecution;
import org.springframework.batch.repeat.RepeatCallback;
import org.springframework.batch.repeat.RepeatContext;
import org.springframework.batch.repeat.RepeatStatus;
import org.springframework.util.ObjectUtils;

/**
 * Convenient base class for clients who need to do something in a repeat callback inside
 * a {@link Step}.
 *
 * @author Dave Syer
 * @author Mahmoud Ben Hassine
 *
 */
public abstract class StepContextRepeatCallback implements RepeatCallback {

	private final Queue<ChunkContext> attributeQueue = new LinkedBlockingQueue<>();

	private final StepExecution stepExecution;

	private final Log logger = LogFactory.getLog(StepContextRepeatCallback.class);

	/**
	 * @param stepExecution instance of {@link StepExecution} to be used by
	 * StepContextRepeatCallback.
	 */
	public StepContextRepeatCallback(StepExecution stepExecution) {
		this.stepExecution = stepExecution;
	}

	/**
	 * Manage the {@link StepContext} lifecycle. Business processing should be delegated
	 * to {@link #doInChunkContext(RepeatContext, ChunkContext)}. This is to ensure that
	 * the current thread has a reference to the context, even if the callback is executed
	 * in a pooled thread. Handles the registration and unregistration of the step
	 * context, so clients should not duplicate those calls.
	 *
	 * @see RepeatCallback#doInIteration(RepeatContext)
	 */
	@Override
	public RepeatStatus doInIteration(RepeatContext context) throws Exception {

		// The StepContext has to be the same for all chunks,
		// otherwise step-scoped beans will be re-initialised for each chunk.
		StepContext stepContext = StepSynchronizationManager.register(stepExecution);
		if (logger.isDebugEnabled()) {
			logger.debug("Preparing chunk execution for StepContext: " + ObjectUtils.identityToString(stepContext));
		}

		ChunkContext chunkContext = attributeQueue.poll();
		if (chunkContext == null) {
			chunkContext = new ChunkContext(stepContext);
		}

		try {
			if (logger.isDebugEnabled()) {
				logger.debug("Chunk execution starting: queue size=" + attributeQueue.size());
			}
			return doInChunkContext(context, chunkContext);
		}
		finally {
			// Still some stuff to do with the data in this chunk,
			// pass it back.
			if (!chunkContext.isComplete()) {
				attributeQueue.add(chunkContext);
			}
			StepSynchronizationManager.close();
		}
	}

	/**
	 * Do the work required for this chunk of the step. The {@link ChunkContext} provided
	 * is managed by the base class, so that if there is still work to do for the task in
	 * hand state can be stored here. In a multi-threaded client, the base class ensures
	 * that only one thread at a time can be working on each instance of
	 * {@link ChunkContext}. Workers should signal that they are finished with a context
	 * by removing all the attributes they have added. If a worker does not remove them
	 * another thread might see stale state.
	 * @param context the current {@link RepeatContext}
	 * @param chunkContext the chunk context in which to carry out the work
	 * @return the repeat status from the execution
	 * @throws Exception implementations can throw an exception if anything goes wrong
	 */
	public abstract RepeatStatus doInChunkContext(RepeatContext context, ChunkContext chunkContext) throws Exception;

}

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