Java多线程下模拟文件下载

来源：互联网发布：linux源码编译mysql 编辑：程序博客网时间：2024/06/03 15:29
将一个文件分为四个部分，采用多线程模拟下载。
public class Test3Download {public static void main(String[] args) {int fileLength = 0;// 1 创建文件对象File file = new File("C:\\123.mp4");// 2 拿到文件的长度if (file.exists()) {fileLength = (int) file.length();}// 拿到每个线程需要执行的长度int length = fileLength % 4 == 0 ? fileLength / 4 : fileLength / 4 + 1;// 如果 取余4 不等于0 每一个就多读取一个字节// 算一下最后一个需要读取的长度// 最后一块的长度int lastLength = fileLength - length * 3;// 启动线程DownLoad l1 = new DownLoad(0, length);// 26 0-25DownLoad l2 = new DownLoad(length, length);// 26-52 第一个lenth 起点// 第二个lenght 长度DownLoad l3 = new DownLoad(2 * length, length);DownLoad l4 = new DownLoad(3 * length, lastLength);// 启动线程l1.start();l2.start();l3.start();l4.start();}}class DownLoad extends Thread {// 需要什么? 需要确定开始的位置 和 读取的长度private int start;private int length;public DownLoad(int start, int length) {super();this.start = start;this.length = length;}@Overridepublic void run() {// 随机读写流// 注意: 一个随机读写流不能同时去读和写,想要读和写,那就创建两个随机读写流对象RandomAccessFile read = null;RandomAccessFile write = null;try {System.out.println(Thread.currentThread().getName() + "开始复制...");read = new RandomAccessFile("C:\\123.mp4", "rw");write = new RandomAccessFile("D:\\1234.mp4", "rw");// 跳过指定的位置read.seek(start);write.seek(start); // 重点标注// 读取 数组的长度和需要读取的数据相同byte[] b = new byte[4096];int len = 0;int i = 0;while (true) {if (length - i < b.length) {read.read(b, 0, length - i);write.write(b, 0, length - i);break;} else {len = read.read(b);i += len;write.write(b, 0, len);}}System.out.println(Thread.currentThread().getName() + "复制完成");} catch (FileNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();} finally {if (read != null) {try {read.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}if (write != null) {try {write.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}}}}
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