package com.duan;
//本程序是利用多线程下载一首mp3
//主程序DownloadTest.java
public class DownloadTest {
public static void main(String[] args) {
DownloadTool.resourceDownload("http://localhost:8080/com/duan/b.mp3");
}
}
//DownloadTool.java
package com.duan;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.*;
public class DownloadTool {
public static void resourceDownload(String path) {
try {
int startPosition = 0;//记录写入文件时的起始位置
int threadCount = 4;//线程数量
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();//打开连接
conn.setRequestMethod("GET");//设置为get请求
conn.setConnectTimeout(6*1000);
conn.setRequestProperty("range", "bytes="+startPosition+"-");
int fileSize = conn.getContentLength();//获取网络资源的大小
int block = fileSize/threadCount+1;//计算每个线程所读取的块的大小
String filename = path.substring(path.lastIndexOf("/")+1);//获取网络资源的文件名
// System.out.println(filename);
// System.out.println("fileSize= "+fileSize);
RandomAccessFile ras = new RandomAccessFile("f:/download/"+filename, "rw");//新建文件，保存在本地
ras.setLength(fileSize);//设置新建文件的大小
ras.close();
//创建4个线程来下载网络资源
for(int i=0;i<threadCount;i++) {
//保存每一个线程下载的block到file
RandomAccessFile file = new RandomAccessFile("f:/download/"+filename,"rw");
startPosition = i*block;//计算写入文件的起始位置
file.seek(startPosition);//把文件指针已到起始位置
System.out.println("the num "+i+" thread started");
new DownloadThread(i,block,url,file).start();//启动线程
}
conn.disconnect();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
//DownloadThread.java
package com.duan;
import java.io.*;
import java.net.*;
public class DownloadThread extends Thread{
private int i;
private int block;
private URL url;
private RandomAccessFile file;
public DownloadThread(int i,int block,URL url,RandomAccessFile file) {
this.i = i;
this.block = block;
this.url = url;
this.file = file;
}
@Override
public void run() {
try {
HttpURLConnection conn = (HttpURLConnection) url.openConnection();//打开连接
conn.setReadTimeout(6*1000);
conn.setRequestMethod("GET");
InputStream is = conn.getInputStream();//从连接获取InputStream
byte[] buf = new byte[1024];//读取的缓冲区
int readSize = 0;//记录线程所读的块大小
int len = 0;
System.out.println("bloack"+i+"= "+block);
while((len=is.read(buf))>0 && readSize<block) {//线程下载文件结束的条件之一是readSize<block
file.write(buf, 0, len);
readSize += len;
}
System.out.println("the num " + i +" thread finished download");
file.close();
is.close();
conn.disconnect();
} catch (IOException e) {
e.printStackTrace();
}
}
}