基于Http的文件断点续传实现【Java技术】

public class MyDownLoadClient {public static String urlpath = "http://127.0.0.1:80/";private static int threadCount = 5;public static void main(String[] args) throws Exception {// 让用户输入要下载的文件名称Scanner sc = new Scanner(System.in);System.out.println("请输入要下载的文件名称:");String file = sc.next();urlpath = urlpath.concat(file);// 获取文件总大小URL url = new URL(urlpath);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");conn.setConnectTimeout(2000);int responseCode = conn.getResponseCode();if (responseCode == 200) {int contentLength = conn.getContentLength();System.out.println("length" + contentLength);int part = contentLength / threadCount;// 读配置文件ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();CountDownLatch count;InputStream in = MyDownLoadClient.class.getClassLoader().getResourceAsStream(file + ".properties");if (in != null) {// 说明该文件不是第一次下载,需要断点续传Properties p = new Properties();p.load(in);in.close();Set<String> keys = p.stringPropertyNames();count = new CountDownLatch(keys.size());for (String key : keys) {String value = p.getProperty(key);String[] arr = value.split(",");long start = Long.parseLong(arr[0]);long end = Long.parseLong(arr[1]);map.put(key,value);new DownloadThread(start, end, key, map, count, file).start();}p.clear();p = null;} else {count = new CountDownLatch(threadCount);// 说明该文件是第一次下载,直接下载即可for (int i = 0; i < threadCount; i++) {long startIndex = i * part; //每个线程起始下载位置long endIndex = (i + 1) * part;//每个线程的结束位置if (i == threadCount - 1) {//最后一个线程的结束位置endIndex = contentLength;}map.put( String.valueOf(i),startIndex+","+endIndex);new DownloadThread(startIndex, endIndex, String.valueOf(i), map, count, file).start();}}// 等待任务完成,删除配置文件count.await();new File(MyDownLoadClient.class.getClassLoader().getResource("").getPath(),file + ".properties").delete();System.out.println("==========================下载任务完成==========================");} else {System.out.println("连接服务器失败...请检查服务器是否畅通及资源路径是否正确...");}}}下载任务的线程代码实现:class DownloadThread extends Thread {private long startIndex;private long endIndex;private String threadId;private ConcurrentHashMap<String, String> map;private CountDownLatch count;//private long subTotal = 0;private String fileName;public DownloadThread(long startIndex, long endIndex, String threadId, ConcurrentHashMap<String, String> map, CountDownLatch count, String fileName) {this.startIndex = startIndex;this.endIndex = endIndex;this.threadId = threadId;this.map = map;this.count = count;this.fileName = fileName;}@Overridepublic void run() {try {URL url = new URL(MyDownLoadClient.urlpath);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");conn.setConnectTimeout(5000);//固定写法，表示向服务器请求部分资源conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);int responseCode = conn.getResponseCode();//状态码206表示请求部分资源成功if (responseCode == 206) {RandomAccessFile rafAccessFile = new RandomAccessFile(fileName, "rw");rafAccessFile.seek(startIndex);InputStream is = conn.getInputStream();int len = -1;byte[] buffer = new byte[1024];Random r = new Random();while ((len = is.read(buffer)) != -1) {FileOutputStream fout = new FileOutputStream(this.getClass().getClassLoader().getResource("").getPath()+"\\"+fileName + ".properties");try {//模拟意外情况导致下载中断的代码/*if (r.nextInt(2) == 0) {int i = 1 / 0;}*/rafAccessFile.write(buffer, 0, len);startIndex += len;map.put(threadId, startIndex + "," + endIndex);} catch (Exception e) {e.printStackTrace();throw new RuntimeException();} finally {Set<Map.Entry<String, String>> entries = map.entrySet();for (Map.Entry<String, String> entry : entries) {fout.write((entry.getKey() + "=" + entry.getValue() + "\r\n").getBytes());}fout.close();}}rafAccessFile.close();System.out.println("线程" + threadId + "下载完成");System.gc();}count.countDown();} catch (Exception e) {e.printStackTrace();System.gc();}}}