java多线程下载器

落日映苍穹つ 2022-08-06 07:30 195阅读 0赞

package myweb;
    
    import java.io.File;
    import java.io.InputStream;
    import java.io.RandomAccessFile;
    import java.net.HttpURLConnection;
    import java.net.URL;
    
    /**
     * 多线程下载文件
     * 
     * @author xiaoxiao
     *
     */
    public class MultiThreadDownLoad {
    
    	public static void main(String[] args) throws Exception {
    		MultiThreadDownLoad download = new MultiThreadDownLoad();
    		download.downLoad("http://localhost:8080/myweb/Thunderbird-Setup-31.0-31.0.0.5311.exe", "d:/", 4);
    	}
    
    	/**
    	 * 多线程下载文件到指定目录
    	 * 
    	 * @param downloadUrl
    	 *            下载URL
    	 * @param filePath
    	 *            保存文件路径
    	 * @param threadSize
    	 *            线程个数
    	 * @throws Exception
    	 */
    	public void downLoad(String downloadUrl, String filePath, int threadSize) throws Exception {
    		URL url = new URL(downloadUrl);
    		HttpURLConnection con = (HttpURLConnection) url.openConnection();
    		con.setConnectTimeout(5000);
    		con.setRequestMethod("GET");
    		if (con.getResponseCode() == 200) {
    			int length = con.getContentLength();
    			File file = new File(getFileName(filePath, downloadUrl));
    			RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
    			accessFile.setLength(length);
    			accessFile.close();
    			// 计算每个线程下载的块数
    			int block = length % threadSize == 0 ? length / threadSize : length / threadSize + 1;
    			for (int threadId = 0; threadId < threadSize; threadId++) {
    				new MultiDownLoad(url, threadId, block, file).start();
    			}
    		}
    		con.disconnect();
    	}
    
    	private String getFileName(String filePath, String downloadUrl) {
    		String fileName = downloadUrl.substring(downloadUrl.lastIndexOf("/") + 1, downloadUrl.length());
    		return filePath + File.separatorChar + fileName;
    	}
    
    	private class MultiDownLoad extends Thread {
    		private URL downloadUrl;
    		private int threadId;
    		private int block;
    		private File file;
    
    		public MultiDownLoad(URL downloadUrl, int threadId, int block, File file) {
    			super();
    			this.downloadUrl = downloadUrl;
    			this.threadId = threadId;
    			this.block = block;
    			this.file = file;
    		}
    
    		@Override
    		public void run() {
    			int start = threadId * block;
    			int end = (threadId + 1) * block - 1;
    			try {
    				RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
    				accessFile.seek(start);
    				HttpURLConnection con = (HttpURLConnection) downloadUrl.openConnection();
    				con.setConnectTimeout(5000);
    				con.setRequestMethod("GET");
    				con.setRequestProperty("Range", "bytes=" + start + "-" + end);
    				if (con.getResponseCode() == 206) {
    					InputStream is = con.getInputStream();
    					byte[] buffer = new byte[1024];
    					int len = 0;
    					while ((len = is.read(buffer)) != -1) {
    						accessFile.write(buffer, 0, len);
    					}
    					is.close();
    					accessFile.close();
    				}
    				con.disconnect();
    				System.out.println("第" + threadId + "个线程读取完成！");
    			} catch (Exception e) {
    				e.printStackTrace();
    			}
    		}
    
    	}
    }