package com.bruce.homework0312.download;
import com.bruce.homework0312.download.api.Connection;
import com.bruce.homework0312.download.api.ConnectionException;
import com.bruce.homework0312.download.api.ConnectionManager;
import com.bruce.homework0312.download.api.DownloadListener;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.util.concurrent.CyclicBarrier;
public class FileDownloader {
private String url;
private String localFile;
private DownloadListener listener;
private ConnectionManager cm;
private static final int DOWNLOAD_THREAD_COUNT = 3;
public FileDownloader(String _url, String localFile) {
this.url = _url;
this.localFile = localFile;
}
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
// 下面的代码是示例代码, 也就是说只有一个线程, 你需要改造成多线程的。
CyclicBarrier barrier = new CyclicBarrier(DOWNLOAD_THREAD_COUNT, new Runnable() {
@Override
public void run() {
listener.notifyFinished();
}
});
Connection conn = null;
try {
conn = cm.open(this.url);
int length = conn.getContentLength();
createPlaceHolderFile(this.localFile, length);
int[][] ranges = allocateDownloadRange(DOWNLOAD_THREAD_COUNT, length);
for (int i = 0; i < DOWNLOAD_THREAD_COUNT; i++) {
DownloadThread thread = new DownloadThread(conn, ranges[i][0], ranges[i][1], localFile, barrier);
thread.start();
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if(conn != null){
conn.close();
}
}
}
//创建一个大小为length的空文件,准备存放下载内容
private void createPlaceHolderFile(String localFile, int length) throws IOException {
RandomAccessFile file = new RandomAccessFile(localFile, "rw");
for (int i = 0; i < length; i++) {
file.write(0);
}
file.close();
}
//根据文件总长度和下载的线程数量,“切分”文件
private int[][] allocateDownloadRange (int threadCount, int totalLength) {
//二维数组第二维长度为2,用于存放startPos和endPo
int[][] ranges = new int[threadCount][2];
int perLen = totalLength / threadCount;
int left = totalLength % threadCount;
for (int i = 0; i < threadCount; i++) {
ranges[i][0] = i * perLen;
ranges[i][1] = (i+1) * perLen - 1;
if (i == (threadCount-1)) {
ranges[i][1] += left;
}
}
return ranges;
}
public void setListener(DownloadListener listener) {
this.listener = listener;
}
public void setConnectionManager(ConnectionManager ucm){
this.cm = ucm;
}
public DownloadListener getListener(){
return this.listener;
}
}