package com.coderising.download;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.CyclicBarrier;
import com.coderising.download.api.Connection;
import com.coderising.download.api.ConnectionManager;
import com.coderising.download.api.DownloadListener;
public class FileDownloader {
private static final int DOWNLOAD_TRHEAD_NUM = 3;
private String url;
private String localFile;
private DownloadListener listener;
private ConnectionManager cm;
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。
/**Connection conn = null;
CountDownLatch threadsCnt = new CountDownLatch(threadNum);
try {
conn = cm.open(this.url);
int length = conn.getContentLength();
RandomAccessFile file = new RandomAccessFile("test", "rw");
file.setLength(length);
new DownloadThread(conn, 0, length - 1, file, threadsCnt).start();
int clength = length / threadNum;
int off = 0;
for (int i = 0; i < threadNum; i++) {
if (i != threadNum - 1) {
new DownloadThread(cm.open(url), off, off + clength, file,threadsCnt).start();
} else {
new DownloadThread(cm.open(url), off, length - 1, file,threadsCnt).start();
}
off = off + clength + 1;
}
threadsCnt.await();
Thread.sleep(5000);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (conn != null) {
conn.close();
}
}**/
CyclicBarrier barrier = new CyclicBarrier(DOWNLOAD_TRHEAD_NUM , new Runnable(){
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_TRHEAD_NUM, length);
for(int i=0; i< DOWNLOAD_TRHEAD_NUM; i++){
DownloadThread thread = new DownloadThread(
cm.open(url),
ranges[i][0],
ranges[i][1],
localFile,
barrier);
thread.start();
}
} catch (Exception e) {
e.printStackTrace();
}finally{
if(conn != null){
conn.close();
}
}
}
private int[][] allocateDownloadRange(int threadNum, int contentLen) {
int[][] ranges = new int[threadNum][2];
int eachThreadSize = contentLen / threadNum;// 每个线程需要下载的文件大小
int left = contentLen % threadNum;// 剩下的归最后一个线程来处理
for(int i=0;i<threadNum;i++){
int startPos = i * eachThreadSize;
int endPos = (i + 1) * eachThreadSize - 1;
if ((i == (threadNum - 1))) {
endPos += left;
}
ranges[i][0] = startPos;
ranges[i][1] = endPos;
}
return ranges;
}
private void createPlaceHolderFile(String fileName, int contentLen) throws IOException {
RandomAccessFile file = new RandomAccessFile(fileName,"rw");
for(int i=0; i<contentLen ;i++){
file.write(0);
}
file.close();
}
public void setListener(DownloadListener listener) {
this.listener = listener;
}
public void setConnectionManager(ConnectionManager ucm) {
this.cm = ucm;
}
public DownloadListener getListener() {
return this.listener;
}
}