本篇内容主要讲解“java线程池怎么实现批量下载文件”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“java线程池怎么实现批量下载文件”吧!

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本文实例为大家分享了java线程池实现批量下载文件的具体代码，供大家参考，具体内容如下

1 创建线程池

package com.cheng.webb.thread;import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.ExecutorService;import java.util.concurrent.ThreadFactory;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicInteger;public class ThreadUtil {  /**   * 创建批量下载线程池   *   * @param threadSize 下载线程数   * @return ExecutorService   */  public static ExecutorService buildDownloadBatchThreadPool(int threadSize) {    int keepAlive = 0;    String prefix = "download-batch";    ThreadFactory factory = ThreadUtil.buildThreadFactory(prefix);    return new ThreadPoolExecutor(threadSize,        threadSize,        keepAlive,        TimeUnit.SECONDS,        new ArrayBlockingQueue<>(threadSize),        factory);  }    /**   * 创建自定义线程工厂   *   * @param prefix 名称前缀   * @return ThreadFactory   */  public static ThreadFactory buildThreadFactory(String prefix) {    return new CustomThreadFactory(prefix);  }      /**   * 自定义线程工厂   */  public static class CustomThreadFactory implements ThreadFactory {    private String threadNamePrefix;    private AtomicInteger counter = new AtomicInteger(1);    /**     * 自定义线程工厂     *     * @param threadNamePrefix 工厂名称前缀     */    CustomThreadFactory(String threadNamePrefix) {      this.threadNamePrefix = threadNamePrefix;    }    @Override    public Thread newThread(Runnable r) {      String threadName = threadNamePrefix + "-t" + counter.getAndIncrement();      return new Thread(r, threadName);    }  }}

2 批量下载文件

package com.cheng.webb.thread;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import java.io.File;import java.io.FileOutputStream;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.URL;import java.util.ArrayList;import java.util.List;import java.util.Map;import java.util.concurrent.*;/** * 文件下载类 *  * @author shucheng * @creation 2019年1月30日下午4:41:32 */public class DownloadUtil { private static Logger logger = LoggerFactory.getLogger(DownloadUtil.class); /** * 下载线程数 */ private static final int DOWNLOAD_THREAD_NUM = 14; /** * 下载线程池 */ private static ExecutorService downloadExecutorService = ThreadUtil  .buildDownloadBatchThreadPool(DOWNLOAD_THREAD_NUM); /** * 文件下载 * * @param fileUrl *      文件url,如:https://img3.doubanio.com//view//photo//s_ratio_poster//public//p2369390663.webp * @param path *      存放路径,如: /opt/img/douban/my.webp */ public static void download(String fileUrl, String path) { // 判断存储文件夹是否已经存在或者创建成功 if (!createFolderIfNotExists(path)) {  logger.error("We can't create folder:{}", getFolder(path));  return; } InputStream in = null; FileOutputStream out = null; try {  URL url = new URL(fileUrl);  HttpURLConnection conn = (HttpURLConnection) url.openConnection();  conn.setRequestMethod("GET");  // 2s  conn.setConnectTimeout(10000);  in = conn.getInputStream();  out = new FileOutputStream(path);  int len;  byte[] arr = new byte[1024 * 1000];  while (-1 != (len = in.read(arr))) {  out.write(arr, 0, len);  }  out.flush();  conn.disconnect(); } catch (Exception e) {  logger.error("Fail to download: {} by {}", fileUrl, e.getMessage()); } finally {  try {  if (null != out) {   out.close();  }  if (null != in) {   in.close();  }  } catch (Exception e) {  // do nothing  } } } /** * 创建文件夹,如果文件夹已经存在或者创建成功返回true * * @param path *      路径 * @return boolean */ private static boolean createFolderIfNotExists(String path) { String folderName = getFolder(path); if (folderName.equals(path)) {  return true; } File folder = new File(getFolder(path)); if (!folder.exists()) {  synchronized (DownloadUtil.class) {  if (!folder.exists()) {   return folder.mkdirs();  }  } } return true; } /** * 获取文件夹 * * @param path *      文件路径 * @return String */ private static String getFolder(String path) { int index = path.lastIndexOf("/"); return -1 != index ? path.substring(0, index) : path; } /** * 下载资源 *

* issue: 线程池创建过多 *

* 最大批量下载为5,请知悉 * * @param resourceMap *      资源map, key为资源下载url,value为资源存储位置 */ public static void batch(Map resourceMap) { if (resourceMap == null || resourceMap.isEmpty()) {  return; } try {  List keys = new ArrayList<>(resourceMap.keySet());  int size = keys.size();  int pageNum = getPageNum(size);  for (int index = 0; index < pageNum; index++) {  int start = index * DOWNLOAD_THREAD_NUM;  int last = getLastNum(size, start + DOWNLOAD_THREAD_NUM);  final CountDownLatch latch = new CountDownLatch(last - start);  // 获取列表子集  List urlList = keys.subList(start, last);  for (String url : urlList) {   // 提交任务   Runnable task = new DownloadWorker(latch, url, resourceMap.get(url));   downloadExecutorService.submit(task);  }  latch.await();  } } catch (Exception e) {  logger.error("{}", e); } logger.info("Download resource map is all done"); } /** * 获取最后一个元素 * * @param size *      列表长度 * @param index *      下标 * @return int */ private static int getLastNum(int size, int index) { return index > size ? size : index; } /** * 获取划分页面数量 * * @param size *      列表长度 * @return int */ private static int getPageNum(int size) { int tmp = size / DOWNLOAD_THREAD_NUM; return size % DOWNLOAD_THREAD_NUM == 0 ? tmp : tmp + 1; } /** * 下载线程 */ static class DownloadWorker implements Runnable { private CountDownLatch latch; private String url; private String path; DownloadWorker(CountDownLatch latch, String url, String path) {  this.latch = latch;  this.url = url;  this.path = path; } @Override public void run() {  logger.debug("Start batch:[{}] into: [{}]", url, path);  DownloadUtil.download(url, path);  logger.debug("Download:[{}] into: [{}] is done", url, path);  latch.countDown(); } }}

3 测试批量下载文件

package com.cheng.webb.thread;import java.util.HashMap;import java.util.Map;import org.junit.Test;import com.alibaba.fastjson.JSON;public class DownLoadTest { String json = "{\r\n"  + " \"http://www.xxx.com/111/123.mp4\":\"myFile/111/123.mp4\",\r\n"  + " \"http://www.xxx.com/111/124.mp4\":\"myFile/111/124.mp4\",\r\n"  + " \"http://www.xxx.com/111/125.mp4\":\"myFile/111/125.mp4\"\r\n"  + "}"; @SuppressWarnings("unchecked") @Test public void test() { Map map = new HashMap<>(); Map resMap = JSON.parseObject(json, map.getClass()); int times = 1; for (int index = 0; index < times; index++) {  DownloadUtil.batch(resMap); } }}

到此，相信大家对“java线程池怎么实现批量下载文件”有了更深的了解，不妨来实际操作一番吧！这里是创新互联网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！

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