package com.coderising.download;
import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
/**
* 多线程下载 和 断点续传
* @author 杨斌.
*
*/
public class Test {
// private String path = "http://mpge.5nd.com/2016/2016-11-15/74847/1.mp3"; //下载路径
private String path = "http://localhost:8080/ForDownload/test.jpg";
private String targetFilePath="/"; //下载文件存放目录
private int threadCount = 3; //线程数量
/**
* 构造方法
* @param path 要下载文件的网络路径
* @param targetFilePath 保存下载文件的目录
* @param threadCount 开启的线程数量,默认为 3
*/
public Test(String path, String targetFilePath, int threadCount) {
this.path = path;
this.targetFilePath = targetFilePath;
this.threadCount = threadCount;
}
public Test() {
}
/**
* 下载文件
*/
public void download() throws Exception{
//连接资源
URL url = new URL(path);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(10000);
int code = connection.getResponseCode();
if(code == 200){
//获取资源大小
int connectionLength = connection.getContentLength();
System.out.println(connectionLength);
//在本地创建一个与资源同样大小的文件来占位
/*RandomAccessFile randomAccessFile = new RandomAccessFile(new File(targetFilePath,getFileName(url)), "rw");
randomAccessFile.setLength(connectionLength);*/
/*
* 将下载任务分配给每个线程
*/
int blockSize = connectionLength/threadCount;//计算每个线程理论上下载的数量.
for(int threadId = 0; threadId < threadCount; threadId++){//为每个线程分配任务
int startIndex = threadId * blockSize; //线程开始下载的位置
int endIndex = (threadId+1) * blockSize -1; //线程结束下载的位置
if(threadId == (threadCount - 1)){ //如果是最后一个线程,将剩下的文件全部交给这个线程完成
endIndex = connectionLength - 1;
}
new DownloadThread(threadId, startIndex, endIndex).start();//开启线程下载
}
// randomAccessFile.close();
}
}
//下载的线程
private class DownloadThread extends Thread{
private int threadId;
private int startIndex;
private int endIndex;
public DownloadThread(int threadId, int startIndex, int endIndex) {
this.threadId = threadId;
this.startIndex = startIndex;
this.endIndex = endIndex;
}
@Override
public void run() {
System.out.println("线程"+ threadId + "开始下载");
try {
//分段请求网络连接,分段将文件保存到本地.
URL url = new URL(path);
//加载下载位置的文件
File downThreadFile = new File(targetFilePath,"downThread_" + threadId+".dt");
RandomAccessFile downThreadStream = null;
if(downThreadFile.exists()){//如果文件存在
downThreadStream = new RandomAccessFile(downThreadFile,"rwd");
String startIndex_str = downThreadStream.readLine();
this.startIndex = Integer.parseInt(startIndex_str);//设置下载起点
}else{
downThreadStream = new RandomAccessFile(downThreadFile,"rwd");
}
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(10000);
//设置分段下载的头信息。 Range:做分段数据请求用的。格式: Range bytes=0-1024 或者 bytes:0-1024
connection.setRequestProperty("Range", "bytes="+ startIndex + "-" + endIndex);
System.out.println("线程_"+threadId + "的下载起点是 " + startIndex + " 下载终点是: " + endIndex);
if(connection.getResponseCode() == 206){//200：请求全部资源成功， 206代表部分资源请求成功
InputStream inputStream = connection.getInputStream();//获取流
RandomAccessFile randomAccessFile = new RandomAccessFile(
new File(targetFilePath,getFileName(url)), "rw");//获取前面已创建的文件.
randomAccessFile.seek(startIndex);//文件写入的开始位置.
/*
* 将网络流中的文件写入本地
*/
byte[] buffer = new byte[1024];
int length = -1;
int total = 0;//记录本次下载文件的大小
while((length = inputStream.read(buffer)) > 0){
randomAccessFile.write(buffer, 0, length);
total += length;
/*
* 将当前现在到的位置保存到文件中
*/
downThreadStream.seek(0);
downThreadStream.write((startIndex + total + "").getBytes("UTF-8"));
}
downThreadStream.close();
inputStream.close();
randomAccessFile.close();
cleanTemp(downThreadFile);//删除临时文件
System.out.println("线程"+ threadId + "下载完毕");
}else{
System.out.println("响应码是" +connection.getResponseCode() + ". 服务器不支持多线程下载");
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
//删除线程产生的临时文件
private synchronized void cleanTemp(File file){
file.delete();
}
//获取下载文件的名称
private String getFileName(URL url){
String filename = url.getFile();
return filename.substring(filename.lastIndexOf("/")+1);
}
public static void main(String[] args) {
try {
new Test().download();
} catch (Exception e) {
e.printStackTrace();
}
}
}