Android---53---多线程下载

使用HttpURLConnection
HttpURLConnection继承自URLConnection，也可用于向指定的网站发送GET请求
POST请求。

方法：

int getResponseCode ():
获取服务器的响应代码

String getResponseMessage ():
获取服务器的响应消息

String getResponseMethod ():
获取发送请求的方法

void setRequestMethod ():
设置发送请求的方法

多线程下载
步骤：

1.创建URL对象
2.获取指定URL对象所指向资源的大小 由getContentLength()实现
3.在本地磁盘上创建一个与网络资源相同大小的空文件
4.计算每条线程应该下载网络资源的那个部分（从哪个字节开始，到哪个字节结束）
5.依次创建、启动多条线程来下载网络资源的指定部分。

下载工具类：

public class DownUtil
{
	// 定义下载资源的路径
	private String path;
	// 指定所下载的文件的保存位置
	private String targetFile;
	// 定义需要使用多少线程下载资源
	private int threadNum;
	// 定义下载的线程对象
	private DownThread[] threads;
	// 定义下载的文件的总大小
	private int fileSize;

	public DownUtil(String path, String targetFile, int threadNum)
	{
		this.path = path;
		this.threadNum = threadNum;
		// 初始化threads数组
		threads = new DownThread[threadNum];
		this.targetFile = targetFile;
	}

	public void download() throws Exception
	{
		URL url = new URL(path);
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		conn.setConnectTimeout(5 * 1000);
		conn.setRequestMethod("GET");
		conn.setRequestProperty(
			"Accept",
			"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
			+ "application/x-shockwave-flash, application/xaml+xml, "
			+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
			+ "application/x-ms-application, application/vnd.ms-excel, "
			+ "application/vnd.ms-powerpoint, application/msword, */*");
		conn.setRequestProperty("Accept-Language", "zh-CN");
		conn.setRequestProperty("Charset", "UTF-8");
		conn.setRequestProperty("Connection", "Keep-Alive");
		// 得到文件大小
		fileSize = conn.getContentLength();
		conn.disconnect();
		int currentPartSize = fileSize / threadNum + 1;
		RandomAccessFile file = new RandomAccessFile(targetFile, "rw");
		// 设置本地文件的大小
		file.setLength(fileSize);
		file.close();
		for (int i = 0; i < threadNum; i++)
		{
			// 计算每条线程的下载的开始位置
			int startPos = i * currentPartSize;
			// 每个线程使用一个RandomAccessFile进行下载
			RandomAccessFile currentPart = new RandomAccessFile(targetFile,
				"rw");
			// 定位该线程的下载位置
			currentPart.seek(startPos);
			// 创建下载线程
			threads[i] = new DownThread(startPos, currentPartSize,
				currentPart);
			// 启动下载线程
			threads[i].start();
		}
	}

	// 获取下载的完成百分比
	public double getCompleteRate()
	{
		// 统计多条线程已经下载的总大小
		int sumSize = 0;
		for (int i = 0; i < threadNum; i++)
		{
			sumSize += threads[i].length;
		}
		// 返回已经完成的百分比
		return sumSize * 1.0 / fileSize;
	}

	private class DownThread extends Thread
	{
		// 当前线程的下载位置
		private int startPos;
		// 定义当前线程负责下载的文件大小
		private int currentPartSize;
		// 当前线程需要下载的文件块
		private RandomAccessFile currentPart;
		// 定义已经该线程已下载的字节数
		public int length;

		public DownThread(int startPos, int currentPartSize,
			RandomAccessFile currentPart)
		{
			this.startPos = startPos;
			this.currentPartSize = currentPartSize;
			this.currentPart = currentPart;
		}

		@Override
		public void run()
		{
			try
			{
				URL url = new URL(path);
				HttpURLConnection conn = (HttpURLConnection)url
					.openConnection();
				conn.setConnectTimeout(5 * 1000);
				conn.setRequestMethod("GET");
				conn.setRequestProperty(
					"Accept",
					"image/gif, image/jpeg, image/pjpeg, image/pjpeg, "
					+ "application/x-shockwave-flash, application/xaml+xml, "
					+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, "
					+ "application/x-ms-application, application/vnd.ms-excel, "
					+ "application/vnd.ms-powerpoint, application/msword, */*");
				conn.setRequestProperty("Accept-Language", "zh-CN");
				conn.setRequestProperty("Charset", "UTF-8");
				InputStream inStream = conn.getInputStream();
				// 跳过startPos个字节，表明该线程只下载自己负责哪部分文件。
				inStream.skip(this.startPos);
				byte[] buffer = new byte[1024];
				int hasRead = 0;
				// 读取网络数据，并写入本地文件
				while (length < currentPartSize
					&& (hasRead = inStream.read(buffer)) > 0)
				{
					currentPart.write(buffer, 0, hasRead);
					// 累计该线程下载的总大小
					length += hasRead;
				}
				currentPart.close();
				inStream.close();
			}
			catch (Exception e)
			{
				e.printStackTrace();
			}
		}
	}
}

Activity：

public class MainActivity extends Activity {

	EditText url;
	EditText target;
	Button downButton;
	ProgressBar bar;
	DownUtil downUtil;

	private int mDownStatus;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);

		url = (EditText) findViewById(R.id.url);
		target = (EditText) findViewById(R.id.target);
		downButton = (Button) findViewById(R.id.down);
		bar = (ProgressBar) findViewById(R.id.bar);

		final Handler handler = new Handler() {
			@Override
			public void handleMessage(Message msg) {
				if (msg.what == 0x123) {
					bar.setProgress(mDownStatus);
				}
			}
		};
		downButton.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				downUtil = new DownUtil(url.getText().toString(), target
						.getText().toString(), 6);
				new Thread() {
					public void run() {
						try {
							downUtil.download();
						} catch (Exception e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
						}

						final Timer timer = new Timer();
						timer.schedule(new TimerTask() {

							@Override
							public void run() {
								// 获取下载任务的完成比率
								double completeRate = downUtil
										.getCompleteRate();
								mDownStatus = (int) (completeRate * 100);
								// 发送消息通知界面更新进度条
								handler.sendEmptyMessage(0x123);
								// 下载完全后取消任务调度
								if (mDownStatus >= 100) {
									timer.cancel();
								}

							}
						}, 0, 100);

					};

				}.start();
			}
		});
	}
}