Android Java 多线程下载文件 demo

package com.zhi.net; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; /** * 开启多条线程完成文件下载至本地 * @author Administrator */ public class DownLoadFile { public static void main(String[] args){ String path = "http://192.168.1.3:8080/FileUpload/kecheng.avi"; try { new DownLoadFile().download(path, 3); } catch (IOException e) { e.printStackTrace(); } } /** * @param path 目标文件的下载地址 * @param threadNum 开启线程的总条数 * @throws IOException */ private void download(String path, int threadNum) throws IOException { URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); int length = conn.getContentLength(); // 获取要下载的文件长度 String fileName = createLocalFile(path, length); int state = conn.getResponseCode(); if(200 == state){ for(int threadId = 0; threadId < threadNum; threadId++){ new DownloadThread(path, fileName, threadId, threadNum, length).start(); } } } /** * 在本地生成同样大小的文件，用来存放下载的数据 * @param path 目标下载地址 * @param length 目标文件的中长度 * @return 生成的本地文件的文件名称 * @throws FileNotFoundException 目标文件不存在 * @throws IOException */ private String createLocalFile(String path, int length) throws FileNotFoundException, IOException { String fileName = path.substring(path.lastIndexOf("/")+1); RandomAccessFile accessFile = new RandomAccessFile(fileName, "rwd"); accessFile.setLength(length); accessFile.close(); return fileName; } } class DownloadThread extends Thread{ private String path; // 要下载的目标地址 private String fileName; // 本地存放文件名 private int threadId; // 第几条线程 private int threadNum; // 第几条线程 private int length; // 总数据的长度 public DownloadThread(String path, String fileName, int threadId, int threadNum, int length) { this.path = path; this.fileName = fileName; this.threadId = threadId; this.threadNum = threadNum; this.length = length; } public void run(){ int block = length%threadNum == 0? length/threadNum : length/threadNum+1; // 每一块的数据量 int start = threadId * block; // 每一个线程的开始位置 int end = (threadId+1)*block-1; // 每一个线程的结束位置 try { RandomAccessFile accessFile = new RandomAccessFile(fileName, "rwd"); accessFile.seek(start); // 将线程中的下载位置赋值给RandomAccessFile(seek类似指针位置) HttpURLConnection conn = (HttpURLConnection) new URL(path).openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); int state = conn.getResponseCode(); if(200 == state){ InputStream in = conn.getInputStream(); byte[] bytes = new byte[1024]; int len = 0; while((len = in.read(bytes)) != -1){ accessFile.write(bytes, 0 , len); } System.out.print("第" + (threadId + 1) + "条线程下载成功"); } accessFile.close(); } catch (IOException e) { e.printStackTrace(); } } }