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这篇文章给大家介绍怎么在java中通过线程池实现批量下载文件，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。
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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);
}
}
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