java多线程分片下载文件

import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.web.client.RestTemplate;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;
@Slf4j
public class SliceUtil {
    /**
     * 分片大小
     */
    public final static long PER_PAGE = (long) 1024 * 1024;
    private static final RestTemplate REST_TEMPLATE = new RestTemplate();
    /**
     * 根据分片下载
     *
     * @param downloadUrl
     * @param start
     * @param end
     * @return
     */
    public static ResponseEntity<byte[]> getFileContentByUrlAndPosition(String downloadUrl, long start, long end) {
        HttpHeaders httpHeaders = new HttpHeaders();
        httpHeaders.set("Range", "bytes=" + start + "-" + end);
        org.springframework.http.HttpEntity<Object> httpEntity = new org.springframework.http.HttpEntity<>(httpHeaders);
        return REST_TEMPLATE.exchange(downloadUrl, HttpMethod.GET, httpEntity, byte[].class);
    }
    /**
     * 下载
     *
     * @param tempPath
     * @param downloadUrl
     * @param sliceInfo
     * @param fName
     */
    public static void download(String tempPath, String downloadUrl, SliceInfo sliceInfo, String fName) {
        log.info("下载分片文件：{}，分片序号 {}", fName, sliceInfo.getPage());
        // 创建一个分片文件对象
        File file = new File(tempPath, sliceInfo.getPage() + "-" + fName);
        if (file.exists() && file.length() == PER_PAGE) {
            log.info("此分片文件 {} 已存在", sliceInfo.getPage());
            return;
        }
        try (FileOutputStream fos = new FileOutputStream(file);) {
            ResponseEntity<byte[]> responseEntity = SliceUtil.getFileContentByUrlAndPosition(downloadUrl, sliceInfo.getStart(), sliceInfo.getEnd());
            byte[] body = responseEntity.getBody();
            if (body != null && body.length == 0) {
                log.warn("分片文件：{},没有内容", file.getName());
                return;
            }
            // 将分片内容写入临时存储分片文件
            fos.write(body);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /**
     * 合并文件
     *
     * @param tempPath
     * @param fName
     * @param page
     */
    public static void mergeFileTranTo(String tempPath, String fName, long page) {
        try (FileChannel channel = new FileOutputStream(new File(tempPath, fName)).getChannel()) {
            for (long i = 1; i <= page; i++) {
                File file = new File(tempPath, i + "-" + fName);
                FileChannel fileChannel = new FileInputStream(file).getChannel();
                long size = fileChannel.size();
                for (long left = size; left > 0; ) {
                    left -= fileChannel.transferTo((size - left), left, channel);
                }
                fileChannel.close();
                file.delete();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

/**
 * 分片页信息
 */
@Data
public class SlicePageInfo {
    private CopyOnWriteArrayList<SliceInfo> sliceInfoList;
    private Long page;
}

import lombok.AllArgsConstructor;
import lombok.Data;
/**
 * 文件分片信息
 */
@Data
@AllArgsConstructor
public class SliceInfo {
    private long start;
    private long end;
    private long page;
}

import com.ruoyi.common.utils.spring.SpringUtils;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpHeaders;
import org.springframework.http.ResponseEntity;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import java.util.Objects;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CountDownLatch;
import static com.ruoyi.download.slice.SliceUtil.PER_PAGE;
@Slf4j
public class DownLoadEngine {
    // 原生线程池
    // private static final ExecutorService executorService = ExecutorFactory.newFixedExecutorService(5);
    // 若依线程池
    private static ThreadPoolTaskExecutor executorService = SpringUtils.getBean("threadPoolTaskExecutor");
    /**
     * 分片下载
     *
     * @param downloadUrl 下载链接
     * @param tempPath    临时文件路径
     * @param fileName    文件名称
     */
    public static void downloadSlice(String downloadUrl, String tempPath, String fileName) {
        //大小探测
        ResponseEntity<byte[]> responseEntity = SliceUtil.getFileContentByUrlAndPosition(downloadUrl, 0, 1);
        HttpHeaders headers = responseEntity.getHeaders();
        String rangeBytes = headers.getFirst("Content-Range");
        if (Objects.isNull(rangeBytes)) {
            log.error("url:{},不支持分片下载", downloadUrl);
            return;
        }
        long allBytes = Long.parseLong(rangeBytes.split("/")[1]);
        log.info("文件总大小：{}M", allBytes / 1024.0 / 1024.0);
        //分页
        SlicePageInfo slicePageInfo = splitPage(allBytes);
        CountDownLatch countDownLatch = new CountDownLatch(Math.toIntExact(slicePageInfo.getPage()));
        CountDownLatch mainLatch = new CountDownLatch(1);
        executorService.execute(() -> {
            try {
                countDownLatch.await();
                SliceUtil.mergeFileTranTo(tempPath, fileName, slicePageInfo.getPage());
                mainLatch.countDown();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        for (SliceInfo sliceInfo : slicePageInfo.getSliceInfoList()) {
            executorService.submit(() -> {
                SliceUtil.download(tempPath, downloadUrl, sliceInfo, fileName);
                countDownLatch.countDown();
            });
        }
        try {
            mainLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    /**
     * 文件分片
     *
     * @param allBytes 文件总大小
     * @return /
     */
    public static SlicePageInfo splitPage(long allBytes) {
        CopyOnWriteArrayList<SliceInfo> list = new CopyOnWriteArrayList<>();
        long size = allBytes;
        long left = 0;
        long page = 0;
        while (size > 0) {
            long start = 0;
            long end;
            start = left;
            //分页
            if (size < PER_PAGE) {
                end = left + size;
            } else {
                end = left += PER_PAGE;
            }
            size -= PER_PAGE;
            page++;
            if (start != 0) {
                start++;
            }
            log.info("页码：{}，开始位置：{}，结束位置：{}", page, start, end);
            final SliceInfo sliceInfo = new SliceInfo(start, end, page);
            list.add(sliceInfo);
        }
        SlicePageInfo slicePageInfo = new SlicePageInfo();
        slicePageInfo.setSliceInfoList(list);
        slicePageInfo.setPage(page);
        return slicePageInfo;
    }
}

@Test
@DisplayName("大文件分片下载")
public void downloadSliceFile() {
    DownLoadEngine.downloadSlice("https://dldir1.qq.com/qqfile/qq/PCQQ9.6.1/QQ9.6.1.28732.exe", "D:/temp", "qq.exe");
}