基于HTTP的多线程文件下载功能实现

思想

文件信息获取的获取方式与单线程的方式一样

与单线程相比不同的是将远程文件分块并发获取，然后再并发写入到本地暂存文件中

远程文件分块的实现依据是：connection.setRequestProperty(“Range”,”bytes=”+start+”-“+end)

本地将文件写入指定位置的实现依据是：RandomAccessFile

代码实现

package org.hanmeis;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicLong;
import java.util.logging.Logger;

/**
* Created by zhao.wu on 2016/12/7.
* 多线程下载器
* 1. 使用{@see RandomAccessFile}在文件任意位置写入内容
* 2. 使用 {@code connection.setRequestProperty("Range","bytes="+start+"-"+end);}设置从服务器上读取的文件块。
*/
public class MuiltDownloader {
private static Log
d9ad
ger logger = Logger.getLogger("MuiltDownloader");

public static void main(String[] args) throws IOException, InterruptedException, ExecutionException {
String url = "http://dlsw.baidu.com/sw-search-sp/soft/e7/40642/Git-2.7.2-64-bit_setup.1457942968.exe";
MuiltDownloader muiltDownloader = new MuiltDownloader(url, 10);
muiltDownloader.connectServer();
muiltDownloader.startDownload();
}

private AtomicLong currentSize = new AtomicLong(0l);
private long preSize;
private long fileSize;
private String realFileName;
private String tempFileName;
private String urlStr;
private int taskNum;
private Timer timer = new Timer();

private MuiltDownloader(String urlStr, int taskNum) {
logger.info("新任务加入下载队列......");
this.urlStr = urlStr;
this.taskNum = taskNum;
this.tempFileName = UUID.randomUUID().toString().replace("-", "");
}

private void connectServer() throws IOException {
URL url = new URL(urlStr);

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.realFileName = temp[temp.length - 1];
}

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

RandomAccessFile randomAccessFile = new RandomAccessFile(tempFileName,"rw");
randomAccessFile.setLength(fileSize);
randomAccessFile.close();
}

private void startDownload() throws InterruptedException, ExecutionException {
long foot = fileSize / taskNum;
long rest = fileSize % taskNum;

List<BlockDownLoadTask> tasks = new ArrayList<>();
for (int i = 0; i < taskNum; i++) {
logger.info(String.format("初始化第%d个下载线程", i+1));
BlockDownLoadTask task;
if (i < taskNum - 1) {
task = new BlockDownLoadTask(tempFileName, urlStr, i * foot, (i + 1) * foot - 1, currentSize);
} else {
task = new BlockDownLoadTask(tempFileName, urlStr, i * foot, fileSize, currentSize);
}
tasks.add(task);
}

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

ExecutorService service = Executors.newFixedThreadPool(taskNum);
service.invokeAll(tasks);
service.shutdownNow();

timer.cancel();

File file = new File(tempFileName);
file.renameTo(new File(realFileName));
logger.info(String.format("完成下载:%s",realFileName));
}

/**
* 定时计算下载状态
*/
private void info(){

timer.schedule(new TimerTask() {
@Override
public void run() {
long tempC = currentSize.get();
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",realFileName, percent, speed));
}
},0, 3000);
}
}

class BlockDownLoadTask implements Callable<String> {
private String tempFileName;
private String urlStr;
private long startPosition;
private long endPosition;
private AtomicLong currentSize;

BlockDownLoadTask(String tempFileName, String urlStr, long startPosition, long endPosition, AtomicLong currentSize) {
this.tempFileName = tempFileName;
this.urlStr = urlStr;
this.startPosition = startPosition;
this.endPosition = endPosition;
this.currentSize = currentSize;
}

@Override
public String call() throws Exception {
URL url = new URL(urlStr);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestProperty("Range", "bytes=" + startPosition + "-" + endPosition);
InputStream is = connection.getInputStream();

RandomAccessFile randomAccessFile = new RandomAccessFile(tempFileName, "rwd");
randomAccessFile.seek(startPosition);

byte[] bs = new byte[1024];
int len;
while ((len = is.read(bs)) > 0) {
randomAccessFile.write(bs);
currentSize.addAndGet(len);
}

randomAccessFile.close();
is.close();
return Thread.currentThread().getName();
}
}