package com.coding2017.week3.download;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import com.coding2017.week3.download.api.Connection;
import com.coding2017.week3.download.api.ConnectionException;
import com.coding2017.week3.download.api.ConnectionManager;
import com.coding2017.week3.download.api.DownloadListener;
public class FileDownloader {
private String url;
private String outFilePath;
private DownloadListener listener;
private ConnectionManager cm;
private int threadCount;
public FileDownloader(String _url, String outFilePath, int threadCount) {
this.url = _url;
this.outFilePath = outFilePath;
this.threadCount = threadCount;
}
public void execute() {
// 在这里实现你的代码, 注意: 需要用多线程实现下载
// 这个类依赖于其他几个接口, 你需要写这几个接口的实现代码
// (1) ConnectionManager , 可以打开一个连接,通过Connection可以读取其中的一段(用startPos, endPos来指定)
// (2) DownloadListener, 由于是多线程下载, 调用这个类的客户端不知道什么时候结束,所以你需要实现当所有
// 线程都执行完以后, 调用listener的notifiedFinished方法, 这样客户端就能收到通知。
// 具体的实现思路:
// 1. 需要调用ConnectionManager的open方法打开连接, 然后通过Connection.getContentLength方法获得文件的长度
// 2. 至少启动3个线程下载, 注意每个线程需要先调用ConnectionManager的open方法
// 然后调用read方法, read方法中有读取文件的开始位置和结束位置的参数, 返回值是byte[]数组
// 3. 把byte数组写入到文件中
// 4. 所有的线程都下载完成以后, 需要调用listener的notifiedFinished方法
try {
int contentLength = getUrlContentLength(url);
FileOutputStream fileOutputStream = new FileOutputStream(outFilePath);
fileOutputStream.write(new byte[contentLength]);
fileOutputStream.flush();
fileOutputStream.close();
for (int i = 0; i < threadCount; i++) {
downloadPart(i, contentLength);
}
} catch (IOException e) {
e.printStackTrace();
}
}
private void downloadPart(int part, int length) {
Connection conn;
try {
conn = cm.open(this.url);
int startPos = part * length / threadCount;
int endPos = Math.min(length - 1, (part + 1) * length / threadCount);
System.out.println("文件总长度: " + length);
new DownloadThread(conn, startPos, endPos, outFilePath, listener).start();
} catch (ConnectionException e) {
e.printStackTrace();
}
}
private int getUrlContentLength(String url) throws IOException {
URL connUrl = new URL(url);
HttpURLConnection urlConnection = (HttpURLConnection) connUrl.openConnection();
int length = urlConnection.getContentLength();
urlConnection.disconnect();
return length;
}
public void setListener(DownloadListener listener) {
this.listener = listener;
}
public void setConnectionManager(ConnectionManager ucm) {
this.cm = ucm;
}
public DownloadListener getListener() {
return this.listener;
}
}