FileDownloader.java

package assignment0305.download;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import assignment0305.download.api.Connection;
import assignment0305.download.api.ConnectionException;
import assignment0305.download.api.ConnectionManager;
import assignment0305.download.api.DownloadListener;

public class FileDownloader {

	String url;

	DownloadListener listener;

	ConnectionManager cm;

	private static final int DEFAULT_THREADS = 3;

	private RandomAccessFile file;

	public FileDownloader(String _url) {
		this.url = _url;

	}

	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;
		try {

			conn = cm.open(this.url);
			int length = conn.getContentLength();
			if (length <= 0) {
				throw new ConnectionException();
			}
			System.out.println(length);
			String path = "F:/Download/";
			String[] strings = url.split("/");
			String name = strings[strings.length - 1];

			File filename = new File(path + name);
			System.out.println(filename);
			file = new RandomAccessFile(filename, "rw");
			file.setLength(length);

			CountDownLatch countDownLatch = new CountDownLatch(DEFAULT_THREADS);

			int lengthForEachThread = length / DEFAULT_THREADS;
			ExecutorService executorService = Executors.newFixedThreadPool(DEFAULT_THREADS);

			DownloadThread thread1 = new DownloadThread(cm.open(url), file, 0, lengthForEachThread - 1, countDownLatch);
			DownloadThread thread2 = new DownloadThread(cm.open(url), file, lengthForEachThread,
					lengthForEachThread * 2 - 1, countDownLatch);
			DownloadThread thread3 = new DownloadThread(cm.open(url), file, lengthForEachThread * 2, length - 1,
					countDownLatch);

			executorService.execute(thread1);
			executorService.execute(thread2);
			executorService.execute(thread3);

			executorService.shutdown();

			countDownLatch.await();

			listener.notifyFinished();

		} catch (ConnectionException | IOException | InterruptedException e) {
			e.printStackTrace();
		} finally {
			try {
				if (file != null)
					file.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

	public void setListener(DownloadListener listener) {
		this.listener = listener;
	}

	public void setConnectionManager(ConnectionManager ucm) {
		this.cm = ucm;
	}

	public DownloadListener getListener() {
		return this.listener;
	}

}