Java 断点续传

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import java.io.File; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; //断点续传 public class Download { public static void down(String URL, long nPos, String savePathAndFile) { try { URL url = new URL(URL); HttpURLConnection httpConnection = (HttpURLConnection) url .openConnection(); // 设置User-Agent httpConnection.setRequestProperty("User-Agent", "NetFox"); // 设置断点续传的开始位置 httpConnection.setRequestProperty("RANGE", "bytes=" + nPos); // 获得输入流 InputStream input = httpConnection.getInputStream(); RandomAccessFile oSavedFile = new RandomAccessFile(savePathAndFile, "rw"); // 定位文件指针到nPos位置 oSavedFile.seek(nPos); byte[] b = new byte[1024]; int nRead; // 从输入流中读入字节流，然后写到文件中 while ((nRead = input.read(b, 0, 1024)) > 0) { (oSavedFile).write(b, 0, nRead); } httpConnection.disconnect(); } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } public static long getRemoteFileSize(String url) { long size = 0; try { HttpURLConnection conn = (HttpURLConnection) (new URL(url)) .openConnection(); size = conn.getContentLength(); conn.disconnect(); } catch (Exception e) { e.printStackTrace(); } return size; } public static void main(String[] args) { String url = "http://www.blogjava.net/breezedancer/archive/2007/07/19/131264.html"; String savePath = "e://"; String fileName = url.substring(url.lastIndexOf("/")); String fileNam=fileName; HttpURLConnection conn = null; try { conn = (HttpURLConnection) (new URL(url)).openConnection(); } catch (Exception e) { e.printStackTrace(); } File file = new File(savePath + fileName); // 获得远程文件大小 long remoteFileSize = getRemoteFileSize(url); System.out.println("远程文件大小="+remoteFileSize); int i = 0; if (file.exists()) { // 先看看是否是完整的，完整，换名字，跳出循环，不完整，继续下载 long localFileSize = file.length(); System.out.println("已有文件大小为:"+localFileSize); if (localFileSize < remoteFileSize) { System.out.println("文件续传"); down(url, localFileSize, savePath + fileName); }else{ System.out.println("文件存在，重新下载"); do{ i++; fileName = fileNam.substring(0, fileNam.indexOf(".")) + "(" + i + ")" + fileNam.substring(fileNam.indexOf(".")); file = new File(savePath + fileName); }while(file.exists()); try { file.createNewFile(); } catch (IOException e) { e.printStackTrace(); } down(url, 0, savePath + fileName); } // 下面表示文件存在，改名字 } else { try { file.createNewFile(); System.out.println("下载中"); down(url, 0, savePath + fileName); } catch (IOException e) { e.printStackTrace(); } } }}