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();
}
}
}
