java線程池怎么實現批量下載文件

本篇內容主要講解“java線程池怎么實現批量下載文件”，感興趣的朋友不妨來看看。本文介紹的方法操作簡單快捷，實用性強。下面就讓小編來帶大家學習“java線程池怎么實現批量下載文件”吧!

本文實例為大家分享了java線程池實現批量下載文件的具體代碼，供大家參考，具體內容如下

1 創建線程池

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 {  /**   * 創建批量下載線程池   *   * @param threadSize 下載線程數   * @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);  }    /**   * 創建自定義線程工廠   *   * @param prefix 名稱前綴   * @return ThreadFactory   */  public static ThreadFactory buildThreadFactory(String prefix) {    return new CustomThreadFactory(prefix);  }      /**   * 自定義線程工廠   */  public static class CustomThreadFactory implements ThreadFactory {    private String threadNamePrefix;    private AtomicInteger counter = new AtomicInteger(1);    /**     * 自定義線程工廠     *     * @param threadNamePrefix 工廠名稱前綴     */    CustomThreadFactory(String threadNamePrefix) {      this.threadNamePrefix = threadNamePrefix;    }    @Override    public Thread newThread(Runnable r) {      String threadName = threadNamePrefix + "-t" + counter.getAndIncrement();      return new Thread(r, threadName);    }  }}

2 批量下載文件

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.*;/** * 文件下載類 *  * @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); /** * 下載線程數 */ private static final int DOWNLOAD_THREAD_NUM = 14; /** * 下載線程池 */ private static ExecutorService downloadExecutorService = ThreadUtil  .buildDownloadBatchThreadPool(DOWNLOAD_THREAD_NUM); /** * 文件下載 * * @param fileUrl *      文件url,如:<code>https://img3.doubanio.com//view//photo//s_ratio_poster//public//p2369390663.webp</code> * @param path *      存放路徑,如: /opt/img/douban/my.webp */ public static void download(String fileUrl, String path) { // 判斷存儲文件夾是否已經存在或者創建成功 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  } } } /** * 創建文件夾,如果文件夾已經存在或者創建成功返回true * * @param path *      路徑 * @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; } /** * 獲取文件夾 * * @param path *      文件路徑 * @return String */ private static String getFolder(String path) { int index = path.lastIndexOf("/"); return -1 != index ? path.substring(0, index) : path; } /** * 下載資源 * <p> * issue: 線程池創建過多 * <p> * 最大批量下載為5,請知悉 * * @param resourceMap *      資源map, key為資源下載url,value為資源存儲位置 */ public static void batch(Map<String, String> resourceMap) { if (resourceMap == null || resourceMap.isEmpty()) {  return; } try {  List<String> 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);  // 獲取列表子集  List<String> urlList = keys.subList(start, last);  for (String url : urlList) {   // 提交任務   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"); } /** * 獲取最后一個元素 * * @param size *      列表長度 * @param index *      下標 * @return int */ private static int getLastNum(int size, int index) { return index > size ? size : index; } /** * 獲取劃分頁面數量 * * @param size *      列表長度 * @return int */ private static int getPageNum(int size) { int tmp = size / DOWNLOAD_THREAD_NUM; return size % DOWNLOAD_THREAD_NUM == 0 ? tmp : tmp + 1; } /** * 下載線程 */ 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 測試批量下載文件

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<String, String> map = new HashMap<>(); Map<String, String> resMap = JSON.parseObject(json, map.getClass()); int times = 1; for (int index = 0; index < times; index++) {  DownloadUtil.batch(resMap); } }}

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