JAVA多线程断点下载原理如图：
代码如下：
import java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.InputStream; import java.io.InputStreamReader; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; public class MutileThreadDownload { /** * 线程的数量 */ private static int threadCount = 3; /** * 每个下载区块的大小 */ private static long blocksize; /** * 正在运行的线程的数量 */ private static int runningThreadCount; /** * @param args * @throws Exception */ public static void main(String[] args) throws Exception { // 服务器文件的路径 String path = "http://192.168.1.100:8080/ff.exe"; URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setRequestMethod("GET"); conn.setConnectTimeout(5000); int code = conn.getResponseCode(); if (code == 200) { long size = conn.getContentLength();// 得到服务端返回的文件的大小 System.out.println("服务器文件的大小：" + size); blocksize = size / threadCount; // 1.首先在本地创建一个大小跟服务器一模一样的空白文件。 File file = new File("temp.exe"); RandomAccessFile raf = new RandomAccessFile(file, "rw"); raf.setLength(size); // 2.开启若干个子线程分别去下载对应的资源。 runningThreadCount = threadCount; for (int i = 1; i <= threadCount; i++) { long startIndex = (i - 1) * blocksize; long endIndex = i * blocksize - 1; if (i == threadCount) { // 最后一个线程 endIndex = size - 1; } System.out.println("开启线程：" + i + "下载的位置：" + startIndex + "~" + endIndex); new DownloadThread(path, i, startIndex, endIndex).start(); } } conn.disconnect(); } private static class DownloadThread extends Thread { private int threadId; private long startIndex; private long endIndex; private String path; public DownloadThread(String path, int threadId, long startIndex, long endIndex) { this.path = path; this.threadId = threadId; this.startIndex = startIndex; this.endIndex = endIndex; } @Override public void run() { try { // 当前线程下载的总大小 int total = 0; File positionFile = new File(threadId + ".txt"); URL url = new URL(path); HttpURLConnection conn = (HttpURLConnection) url .openConnection(); conn.setRequestMethod("GET"); // 接着从上一次的位置继续下载数据 if (positionFile.exists() && positionFile.length() > 0) {// 判断是否有记录 FileInputStream fis = new FileInputStream(positionFile); BufferedReader br = new BufferedReader( new InputStreamReader(fis)); // 获取当前线程上次下载的总大小是多少 String lasttotalstr = br.readLine(); int lastTotal = Integer.valueOf(lasttotalstr); System.out.println("上次线程" + threadId + "下载的总大小：" + lastTotal); startIndex += lastTotal; total += lastTotal;// 加上上次下载的总大小。 fis.close(); } conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex); conn.setConnectTimeout(5000); int code = conn.getResponseCode(); System.out.println("code=" + code); InputStream is = conn.getInputStream(); File file = new File("temp.exe"); RandomAccessFile raf = new RandomAccessFile(file, "rw"); // 指定文件开始写的位置。 raf.seek(startIndex); System.out.println("第" + threadId + "个线程：写文件的开始位置：" + String.valueOf(startIndex)); int len = 0; byte[] buffer = new byte[512]; while ((len = is.read(buffer)) != -1) { RandomAccessFile rf = new RandomAccessFile(positionFile, "rwd"); raf.write(buffer, 0, len); total += len; rf.write(String.valueOf(total).getBytes()); rf.close(); } is.close(); raf.close(); } catch (Exception e) { e.printStackTrace(); } finally { // 只有所有的线程都下载完毕后 才可以删除记录文件。 synchronized (MutileThreadDownload.class) { System.out.println("线程" + threadId + "下载完毕了"); runningThreadCount--; if (runningThreadCount < 1) { System.out.println("所有的线程都工作完毕了。删除临时记录的文件"); for (int i = 1; i <= threadCount; i++) { File f = new File(i + ".txt"); System.out.println(f.delete()); } } } } } } } 以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持武林网。