sdk手册---并发下载文件丢失

我按照sdk手册---java里面文件下载的并发下载，为什么在下载的过程中会出现丢文件。
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.io.RandomAccessFile;
import java.io.Writer;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

import com.aliyun.oss.ClientException;
import com.aliyun.oss.OSSClient;
import com.aliyun.oss.OSSException;
import com.aliyun.oss.model.GetObjectRequest;
import com.aliyun.oss.model.OSSObject;
import com.aliyun.oss.model.ObjectMetadata;
import com.aliyun.oss.model.PutObjectRequest;

/**

• This sample demonstrates how to download an object concurrently
• from Aliyun OSS using the OSS SDK for Java.
  */

public class ConcurrentGetObjectSample {

private static String endpoint = "*** Provide OSS endpoint ***";
private static String accessKeyId = "*** Provide your AccessKeyId ***";
private static String accessKeySecret = "*** Provide your AccessKeySecret ***";

private static OSSClient client = null;

private static String bucketName = "*** Provide bucket name ***";
private static String key = "*** Provide object key ***";
private static String localFilePath = "*** Provide local file path ***";

private static ExecutorService executorService = Executors.newFixedThreadPool(5);
private static AtomicInteger completedBlocks = new AtomicInteger(0);

public static void main(String[] args) throws IOException {
    /*
     * Constructs a client instance with your account for accessing OSS
     */
    client = new OSSClient(endpoint, accessKeyId, accessKeySecret);

    try {            
        /*
         * Upload an object to your bucket
         */
        System.out.println("Uploading a new object to OSS from a file\n");
        client.putObject(new PutObjectRequest(bucketName, key, createSampleFile()));

        /*
         * Get size of the object and pre-create a random access file to hold object data
         */
        ObjectMetadata metadata = client.getObjectMetadata(bucketName, key);
        long objectSize = metadata.getContentLength();
        RandomAccessFile raf = new RandomAccessFile(localFilePath, "rw");
        raf.setLength(objectSize);
        raf.close();

        /*
         * Calculate how many blocks to be divided
         */
        final long blockSize = 5 * 1024 * 1024L;   // 5MB
        int blockCount = (int) (objectSize / blockSize);
        if (objectSize % blockSize != 0) {
            blockCount++;
        }
        System.out.println("Total blocks count " + blockCount + "\n");

        /*
         * Download the object concurrently
         */
        System.out.println("Start to download " + key + "\n");
        for (int i = 0; i < blockCount; i++) {
            long startPos = i * blockSize;
            long endPos = (i + 1 == blockCount) ? objectSize : (i + 1) * blockSize;
            executorService.execute(new BlockFetcher(startPos, endPos, i + 1));
        }

        /*
         * Waiting for all blocks finished
         */
        executorService.shutdown();
        while (!executorService.isTerminated()) {
            try {
                executorService.awaitTermination(5, TimeUnit.SECONDS);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        /*
         * Verify whether all blocks are finished
         */
        if (completedBlocks.intValue() != blockCount) {
            throw new IllegalStateException("Download fails due to some blocks are not finished yet");
        } else {
            System.out.println("Succeed to download object " + key);
        }

    } catch (OSSException oe) {
        System.out.println("Caught an OSSException, which means your request made it to OSS, "
                + "but was rejected with an error response for some reason.");
        System.out.println("Error Message: " + oe.getErrorCode());
        System.out.println("Error Code:       " + oe.getErrorCode());
        System.out.println("Request ID:      " + oe.getRequestId());
        System.out.println("Host ID:           " + oe.getHostId());
    } catch (ClientException ce) {
        System.out.println("Caught an ClientException, which means the client encountered "
                + "a serious internal problem while trying to communicate with OSS, "
                + "such as not being able to access the network.");
        System.out.println("Error Message: " + ce.getMessage());
    } finally {
        /*
         * Do not forget to shut down the client finally to release all allocated resources.
         */
        if (client != null) {
            client.shutdown();
        }
    }
}

private static class BlockFetcher implements Runnable {

    private long startPos;
    private long endPos;

    private int blockNumber;

    public BlockFetcher(long startPos, long endPos, int blockNumber) {
        this.startPos = startPos;
        this.endPos = endPos;
        this.blockNumber = blockNumber;
    }

    @Override
    public void run() {
        RandomAccessFile raf = null;
        try {
            raf = new RandomAccessFile(localFilePath, "rw");
            raf.seek(startPos);

            OSSObject object = client.getObject(new GetObjectRequest(bucketName, key)
                .withRange(startPos, endPos));
            InputStream objectContent = object.getObjectContent();
            try {
                byte[] buf = new byte[4096];
                int bytesRead = 0;
                while ((bytesRead = objectContent.read(buf)) != -1) {
                    raf.write(buf, 0, bytesRead);
                }

                completedBlocks.incrementAndGet();
                System.out.println("Block#" + blockNumber + " done\n");
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                objectContent.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (raf != null) {
                try {
                    raf.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    } 
}

private static File createSampleFile() throws IOException {
    File file = File.createTempFile("oss-java-sdk-", ".txt");
    file.deleteOnExit();

    Writer writer = new OutputStreamWriter(new FileOutputStream(file));
    for (int i = 0; i < 1000000; i++) {
        writer.write("abcdefghijklmnopqrstuvwxyz\n");
        writer.write("0123456789011234567890\n");
    }
    writer.close();

    return file;
}

}
有谁知道的麻烦告知，debug的时候就是正常的，是否是线程的问题？