- import java.io.*;
- import java.net.*;
- //定义下载从start到end的内容的线程
- class DownThread extends Thread
- {
- //定义字节数组(取水的竹筒)的长度
- private final int BUFF_LEN = 32;
- //定义下载的起始点
- private long start;
- //定义下载的结束点
- private long end;
- //下载资源对应的输入流
- private InputStream is;
- //将下载到的字节输出到raf中
- private RandomAccessFile raf ;
- //构造器,传入输入流,输出流和下载起始点、结束点
- public DownThread(long start , long end
- , InputStream is , RandomAccessFile raf)
- {
- //输出该线程负责下载的字节位置
- System.out.println(start + "---->" + end);
- this.start = start;
- this.end = end;
- this.is = is;
- this.raf = raf;
- }
- public void run()
- {
- try
- {
- is.skip(start);
- raf.seek(start);
- //定义读取输入流内容的的缓存数组(竹筒)
- byte[] buff = new byte[BUFF_LEN];
- //本线程负责下载资源的大小
- long contentLen = end - start;
- //定义最多需要读取几次就可以完成本线程的下载
- long times = contentLen / BUFF_LEN + 4;
- //实际读取的字节数
- int hasRead = 0;
- for (int i = 0; i < times ; i++)
- {
- hasRead = is.read(buff);
- //如果读取的字节数小于0,则退出循环!
- if (hasRead < 0)
- {
- break;
- }
- raf.write(buff , 0 , hasRead);
- }
- }
- catch (Exception ex)
- {
- ex.printStackTrace();
- }
- //使用finally块来关闭当前线程的输入流、输出流
- finally
- {
- try
- {
- if (is != null)
- {
- is.close();
- }
- if (raf != null)
- {
- raf.close();
- }
- }
- catch (Exception ex)
- {
- ex.printStackTrace();
- }
- }
- }
- }
- public class MutilDown
- {
- public static void main(String[] args)
- {
- final int DOWN_THREAD_NUM = 4;
- final String OUT_FILE_NAME = "down.jpg";
- InputStream[] isArr = new InputStream[DOWN_THREAD_NUM];
- RandomAccessFile[] outArr = new RandomAccessFile[DOWN_THREAD_NUM];
- try
- {
- //创建一个URL对象
- URL url = new URL("http://photo.jokeji.cn/"
- + "UpFilesnew/2011/5/24/2011524223829861.gif");
- //以此URL对象打开第一个输入流
- isArr[0] = url.openStream();
- long fileLen = getFileLength(url);
- System.out.println("网络资源的大小" + fileLen);
- //以输出文件名创建第一个RandomAccessFile输出流
- outArr[0] = new RandomAccessFile(OUT_FILE_NAME , "rw");
- //创建一个与下载资源相同大小的空文件
- for (int i = 0 ; i < fileLen ; i++ )
- {
- outArr[0].write(0);
- }
- //每线程应该下载的字节数
- long numPerThred = fileLen / DOWN_THREAD_NUM;
- //整个下载资源整除后剩下的余数
- long left = fileLen % DOWN_THREAD_NUM;
- for (int i = 0 ; i < DOWN_THREAD_NUM; i++)
- {
- //为每个线程打开一个输入流、一个RandomAccessFile对象,
- //让每个线程分别负责下载资源的不同部分。
- if (i != 0)
- {
- //以URL打开多个输入流
- isArr[i] = url.openStream();
- //以指定输出文件创建多个RandomAccessFile对象
- outArr[i] = new RandomAccessFile(OUT_FILE_NAME , "rw");
- }
- //分别启动多个线程来下载网络资源
- if (i == DOWN_THREAD_NUM - 1 )
- {
- //最后一个线程下载指定numPerThred+left个字节
- new DownThread(i * numPerThred , (i + 1) * numPerThred + left
- , isArr[i] , outArr[i]).start();
- }
- else
- {
- //每个线程负责下载一定的numPerThred个字节
- new DownThread(i * numPerThred , (i + 1) * numPerThred
- , isArr[i] , outArr[i]).start();
- }
- }
- }
- catch (Exception ex)
- {
- ex.printStackTrace();
- }
- }
- //定义获取指定网络资源的长度的方法
- public static long getFileLength(URL url) throws Exception
- {
- long length = 0;
- //打开该URL对应的URLConnection。
- URLConnection con = url.openConnection();
- //获取连接URL资源的长度
- long size = con.getContentLength();
- length = size;
- return length;
- }
- }
- //该片段来自于http://www.codesnippet.cn/detail/210620134201.html
来源: http://www.codesnippet.cn/detail/210620134201.html