多线程断点续传

public class DownloadRunnable implements Runnable{
	private int total=0;//标识下载进度
	private int begin;
	private int end;
	private File file;
	private URL url;
	private int id;
	private boolean downloading;
	private List<HashMap<String, Integer>> threadList;
	public DownloadRunnable(int begin, int end, File file, URL url, int id,List<HashMap<String, Integer>> threadList,boolean downloading) {
		this.begin = begin;
		this.end = end;
		this.file = file;
		this.url = url;
		this.id = id;
		this.threadList=threadList;
		this.downloading=downloading;
	}
	@Override
	public void run() {
		if(begin>end) {
			return;
		}
		try {
			HttpURLConnection conn = (HttpURLConnection) url.openConnection();
			conn.setRequestMethod("GET");
			conn.setRequestProperty("User-Agent","Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0");
			conn.setRequestProperty("Range","bytes="+begin+"-"+end);
			InputStream is=conn.getInputStream();
				byte[] buf=new byte[1024*1024];
				RandomAccessFile randomFile=new RandomAccessFile(file,"rw");
				randomFile.seek(begin);
				int len=0;
				HashMap<String, Integer> map=threadList.get(id);
				while((len=is.read(buf))!=-1&&downloading==true){
				randomFile.write(buf,0,len);
				updateProgress(len);
				map.put("finished", map.get("finished")+len);
				System.out.println("下载进度"+total);
				}
				is.close();
				randomFile.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	synchronized private void updateProgress(int add) {
		total+=add;
	}
}

public class DownTest {
	private boolean downloading=false;//标识是否在下载
	private URL url;
	private File file;
	private List<HashMap<String, Integer>> threadList;
	public void down() {
		if(downloading) {//正在下载时,变为暂停
			downloading=false;
			return;
		}
		downloading=true;//变为下载
		if(threadList.size()==0) {//开始线程
			new Thread(new Runnable() {
				@Override
				public void run() {
					try {
						url=new URL("https://files.cnblogs.com/files/阿里巴巴Java开发手册终极版v1.3.0.pdf");
						HttpURLConnection conn=(HttpURLConnection) url.openConnection();
						conn.setRequestMethod("GET");
						conn.setConnectTimeout(5000);
						conn.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:61.0) Gecko/20100101 Firefox/61.0");
						int length=conn.getContentLength();
						if(length<0) {//文件不存在
							return;
						}
						file=new File("d:\\", getFileName("https://files.cnblogs.com/files/阿里巴巴Java开发手册终极版v1.3.0.pdf"));
						RandomAccessFile randomFile=new RandomAccessFile(file, "rw");
						randomFile.setLength(length);
						int blockSize=length/3;
						for (int i = 0; i < 3; i++) {
							int begin=i*blockSize;
							int end=(i+1)*blockSize;
							if(i==2) {
								end=length;
							}
							HashMap<String, Integer> map=new HashMap<String,Integer>();
							map.put("begin", begin);
							map.put("end", end);
							map.put("finished", 0);
							threadList.add(map);
							//创建新的线程,下载文件
							Thread t=new Thread(new DownloadRunnable(begin, end, file, url, i,threadList,downloading));
							t.start();
						}
					} catch (MalformedURLException e) {
						e.printStackTrace();
					} catch (IOException e) {
						e.printStackTrace();
					}
				}
			}).start();
		}else {//恢复线程
				for(int i=0;i<threadList.size();i++){
					HashMap<String,Integer> map=threadList.get(i);
					int begin=map.get("begin");
					int end=map.get("end");
					int finished=map.get("finished");
					Thread t=new Thread(new DownloadRunnable(begin+finished,end,file,url,i,threadList,downloading));
					t.start();
					}
		}
	}
	//获取文件名
	public String getFileName(String url) {
		int index=url.lastIndexOf("/")+1;
		return url.substring(index);
	}
}