Java基础-多线程下载(网络编程-多线程)

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 MultiDownload {

static int ThreadCount = 3;
static int finishedThread = 0;
//确定下载地址
static String path = "http://172.16.20.34:8080/mytest/kugou.exe";
public static void main(String[] args) {

//发送get请求，请求这个地址的资源
try {
URL url = new URL(path);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setReadTimeout(5000);

if(conn.getResponseCode() == 200){
//拿到所请求资源文件的长度
int length = conn.getContentLength();

File file = new File("QQPlayer.exe");
//生成临时文件
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//设置临时文件的大小
raf.setLength(length);
raf.close();
//计算出每个线程应该下载多少字节
int size = length / ThreadCount;

for (int i = 0; i < ThreadCount; i++) {
//计算线程下载的开始位置和结束位置
int startIndex = i * size;
int endIndex = (i + 1) * size - 1;
//如果是最后一个线程，那么结束位置写死
if(i == ThreadCount - 1){
endIndex = length - 1;
}
//					System.out.println("线程" + i + "的下载区间是：" + startIndex + "---" + endIndex);
new DownLoadThread(startIndex, endIndex, i).start();
}
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}
class DownLoadThread extends Thread{
int startIndex;
int endIndex;
int threadId;

public DownLoadThread(int startIndex, int endIndex, int threadId) {
super();
this.startIndex = startIndex;
this.endIndex = endIndex;
this.threadId = threadId;
}

@Override
public void run() {
//再次发送http请求，下载原文件
try {
File progressFile = new File(threadId + ".txt");
//判断进度临时文件是否存在
if(progressFile.exists()){
FileInputStream fis = new FileInputStream(progressFile);
BufferedReader br = new BufferedReader(new InputStreamReader(fis));
//从进度临时文件中读取出上一次下载的总进度，然后与原本的开始位置相加，得到新的开始位置
startIndex += Integer.parseInt(br.readLine());
fis.close();
}
System.out.println("线程" + threadId + "的下载区间是：" + startIndex + "---" + endIndex);
HttpURLConnection conn;
URL url = new URL(MultiDownload.path);
conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(5000);
conn.setReadTimeout(5000);
//设置本次http请求所请求的数据的区间
conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);

//请求部分数据，相应码是206
if(conn.getResponseCode() == 206){
//流里此时只有1/3原文件的数据
InputStream is = conn.getInputStream();
byte[] b = new byte[1024];
int len = 0;
int total = 0;
//拿到临时文件的输出流
File file = new File("QQPlayer.exe");
RandomAccessFile raf = new RandomAccessFile(file, "rwd");
//把文件的写入位置移动至startIndex
raf.seek(startIndex);
while((len = is.read(b)) != -1){
//每次读取流里数据之后，同步把数据写入临时文件
raf.write(b, 0, len);
total += len;
//					System.out.println("线程" + threadId + "下载了" + total);

//生成一个专门用来记录下载进度的临时文件
RandomAccessFile progressRaf = new RandomAccessFile(progressFile, "rwd");
//每次读取流里数据之后，同步把当前线程下载的总进度写入进度临时文件中
progressRaf.write((total + "").getBytes());
progressRaf.close();
}
System.out.println("线程" + threadId + "----------下载完毕-----------");
raf.close();

MultiDownload.finishedThread++;
synchronized (MultiDownload.path) {
if(MultiDownload.finishedThread == MultiDownload.ThreadCount){
for (int i = 0; i < MultiDownload.ThreadCount; i++) {
File f = new File(i + ".txt");
f.delete();
}
MultiDownload.finishedThread = 0;
}
}

}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}