基于HTTP的单线程文件下载功能实现

思路

代码实现

package org.hanmeis;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Scanner;
import java.util.Timer;
import java.util.TimerTask;
import java.util.logging.Logger;

/**
* Created by zhao.wu on 2016/12/7.
* 单线程下载
* 使用方法：SingleDownloader [url]
*/
public class SingleDownloader {
private static Logger logger = Logger.getLogger("SingleDownloader");

public static void main(String[] args) throws IOException {
String url;
if(args.length<1){
System.out.print("输入下载地址：");
url = new Scanner(System.in).nextLine();
}else {
url = args[0];
}

//校验参数合法性 略

SingleDownloader singleDownloader = new SingleDownloader(url);
singleDownloader.connectServer();
singleDownloader.startDownload();
}

private URL url;
private String fileName;
private long fileSize;
private long preSize;
private long currentSize;
private InputStream is;
private OutputStream os;
private Timer timer = new Timer();

private SingleDownloader(){
logger.info("新任务加入下载队列......");
}

private SingleDownloader(String url) throws MalformedURLException {
this();
this.url = new URL(url);
}

/**
* 连接远程服务器，并获取文件信息：大小，文件名
* @throws IOException
*/
private void connectServer() throws IOException {
logger.info(String.format("连接服务器：%s://%s",url.getProtocol(),url.getHost()));

HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setConnectTimeout(10*1000);

this.fileSize = Long.parseLong(connection.getHeaderField("Content-Length"));

String[] temp = url.getFile().split("/");
if(temp.length!=0) {
this.fileName = temp[temp.length - 1];
}

this.is =  connection.getInputStream();
this.os = new FileOutputStream(this.fileName);

logger.info(String.format("文件名：%s  大小：%.2fM", this.fileName, this.fileSize*1.0/1024/1024));
}

/**
* 下载过程
* @throws IOException
*/
private void startDownload() throws IOException {

logger.info(String.format("开始下载:%s",fileName));
info();

byte[] bs = new byte[5120];
int len;
while((len = is.read(bs))>0){
os.write(bs);
this.currentSize += len;
}
is.close();
os.close();
timer.cancel();
logger.info(String.format("完成下载:%s",fileName));
}

/**
* 定时计算下载状态
*/
private void info(){
timer.schedule(new TimerTask() {
@Override
public void run() {
long tempC = currentSize;
long tempSize = tempC-preSize;
preSize = tempC;
double percent = (tempC*100.0)/fileSize;
double speed = (tempSize*1.0)/1024/3;
logger.info(String.format("文件：%s 已完成：%.2f%%  速率：%.2fkb/s",fileName, percent, speed));
}
},0, 3000);
}
}