batch.demo.job.MultiThreadedFlatFileItemReader.java Source code

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Here is the source code for batch.demo.job.MultiThreadedFlatFileItemReader.java

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/*
 * Copyright 2006-2013 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
 *
 *      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 batch.demo.job;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

import org.springframework.batch.item.ExecutionContext;
import org.springframework.batch.item.ItemStreamException;
import org.springframework.batch.item.file.BufferedReaderFactory;
import org.springframework.batch.item.file.FlatFileItemReader;
import org.springframework.core.io.Resource;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;

/**
 * A multi-threaded aware {@link FlatFileItemReader} implementation
 * that starts at the offset specified in bytes relative to the file begin
 * and reads maxItemCount items/lines from the file.
 * The offset and number of items to read is passed vie ExecutionContext
 * parameters set by the {@link FlatFilePartitioner}
 * <p/>
 * Reads all the file by default.
 * 
 * The usage is similar to the {@link FlatFileItemReader}. The <tt>reource</tt>, <tt>maxItemCount</tt>, <tt>startAt</tt>
 * properties can be set from the <tt>stepExecutionContext</tt> populated by the {@link FlatFilePartitioner}:
 * <p/>
 * <pre>
 * {@code <bean id="partitioner" class="org.springframework.batch.core.partition.support.FlatFilePartitioner" scope="step"
 *          p:resource="#{jobParameters['input.file']}" /&gt;
 *          
 *  &lt;bean id="myReader" class="org.springframework.batch.item.file.MultiThreadedFlatFileItemReader" scope="step"&gt;
 *     ...
 *      &lt;property name="resource" value="#{stepExecutionContext['resource']}"/&gt;
 *      &lt;property name="maxItemCount" value="#{stepExecutionContext['itemsCount']}" /&gt;
 *      &lt;property name="startAt" value="#{stepExecutionContext['startAt']}"/&gt;
 *  &lt;/bean&gt;
 * </pre>
 * @author Sergey Shcherbakov
 */
public class MultiThreadedFlatFileItemReader<T> extends FlatFileItemReader<T> {

    /**
     * The number of bytes the partition should skip on startup.
     */
    public static final String START_AT_KEY = "start.at";

    private long startAt = 0;

    public MultiThreadedFlatFileItemReader() {
        setName(ClassUtils.getShortName(MultiThreadedFlatFileItemReader.class));
    }

    /**
     * Sets the byte offset within the file at which this instance should start reading. Set
     * to 0 by default so that this instance starts at the first item.
     *
     * @param startAt the byte offset at which this instance should
     * start reading
     */
    public void setStartAt(long startAt) {
        this.startAt = startAt;
    }

    @Override
    public void open(ExecutionContext executionContext) throws ItemStreamException {
        if (isSaveState()) {
            Assert.notNull(executionContext, "ExecutionContext must not be null");
            if (executionContext.containsKey(getExecutionContextUserSupport().getKey(START_AT_KEY))) {
                startAt = executionContext.getLong(getExecutionContextUserSupport().getKey(START_AT_KEY));
            }
        }
        // replace the DefaultBufferedReaderFactory with an implementation that seeks to the start before reading
        setBufferedReaderFactory(new BufferedFileReaderFactory(this.startAt));
        super.open(executionContext);
    }

    @Override
    public void update(ExecutionContext executionContext) throws ItemStreamException {
        super.update(executionContext);
        if (isSaveState()) {
            executionContext.putLong(getExecutionContextUserSupport().getKey(START_AT_KEY), startAt);
        }
    }

    public static class BufferedFileReaderFactory implements BufferedReaderFactory {

        private long skipBytes;

        public BufferedFileReaderFactory() {
            this(0L);
        }

        public BufferedFileReaderFactory(long skipBytes) {
            this.skipBytes = skipBytes;
        }

        /* (non-Javadoc)
         * @see org.springframework.batch.item.file.BufferedReaderFactory#create(org.springframework.core.io.Resource, java.lang.String)
         */
        public BufferedReader create(Resource resource, String encoding)
                throws UnsupportedEncodingException, IOException {
            FileInputStream fis = new FileInputStream(resource.getFile());
            fis.skip(this.skipBytes);
            return new BufferedReader(new InputStreamReader(fis, encoding));
        }

        public void setSkipBytes(long skipBytes) {
            this.skipBytes = skipBytes;
        }

    }

}