Android学习 多线程 下载

新版的多线程 下载 下载log放到了txt中 比较浅显和简单 但是还有些需要改进的地方c

package cn.itcast.mutiledownload;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class DemoActivity extends Activity implements OnClickListener {

	private ProgressBar pb;
	private Button bt;
	private TextView tv;
	private EditText et;
	boolean flag = true;
	boolean stopflag = false;
	private Handler handler = new Handler() {

		@Override
		public void handleMessage(Message msg) {
			pb.setProgress(total);

			int max = pb.getMax();
			if (total >= (max - 1)) {
				total = max;
				flag = false;
			}
			int result = total * 100 / max;
			tv.setText("当前进度 :" + result + "%");

			super.handleMessage(msg);
		}
	};

	int total = 0;

	@Override
	public void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		pb = (ProgressBar) this.findViewById(R.id.pb);
		bt = (Button) this.findViewById(R.id.bt);
		tv = (TextView) this.findViewById(R.id.tv_process);
		et = (EditText) this.findViewById(R.id.et);
		bt.setOnClickListener(this);

	}

	@Override
	public void onClick(View v) {
		switch (v.getId()) {
		case R.id.bt:
			// 创建一个子线程 定期的更新ui

			if("开始下载".equals(bt.getText().toString())){
				bt.setText("暂停");
				stopflag = false; //开始下载 
			}
			else {
				bt.setText("开始下载");
				stopflag = true;
			}
				new Thread() {

					@Override
					public void run() {
						super.run();
						while (flag) {
							try {
								sleep(1000);
								// 如果total > = 文件长度
								Message msg = new Message();
								handler.sendMessage(msg);
							} catch (InterruptedException e) {
								e.printStackTrace();
							}

						}
					}
				}.start();

				// 开始执行下载的操作
				String path = et.getText().toString().trim();
				if ("".equals(path)) {
					Toast.makeText(this, "路径不能为空", 1).show();
					return;
				}
				try {
					URL url = new URL(path);
					HttpURLConnection conn = (HttpURLConnection) url
							.openConnection();
					conn.setRequestMethod("GET");
					conn.setConnectTimeout(5000);
					conn.setRequestProperty("User-Agent",
							"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
					int code = conn.getResponseCode();
					if (code == 200) {
						int len = conn.getContentLength();
						RandomAccessFile file = new RandomAccessFile(
								"/mnt/sdcard/" + getFilenName(path), "rwd");
						// 1.设置本地文件大小跟服务器的文件大小一致
						file.setLength(len);
						// 设置进度条的最大值
						pb.setMax(len);

						// 2 .假设开启3 个线程
						int threadnumber = 3;
						int blocksize = len / threadnumber;
						/**
						 * 线程1 0~ blocksize 线程2 1*bolocksize ~ 2*blocksize 线程3
						 * 2*blocksize ~ 文件末尾
						 */
						for (int i = 0; i < threadnumber; i++) {
							int startposition = i * blocksize;
							int endpositon = (i + 1) * blocksize;
							if (i == (threadnumber - 1)) {
								// 最后一个线程
								endpositon = len;
							}

							DownLoadTask task = new DownLoadTask(i, path,
									startposition, endpositon);
							task.start();
						}

					}
				} catch (Exception e) {
					Toast.makeText(this, "下载出现异常", 0).show();
					e.printStackTrace();
				}
			
			break;
		}

	}

	class DownLoadTask extends Thread {

		int threadid;
		String filepath;
		int startposition;
		int endpositon;

		public DownLoadTask(int threadid, String filepath, int startposition,
				int endpositon) {
			this.threadid = threadid;
			this.filepath = filepath;
			this.startposition = startposition;
			this.endpositon = endpositon;

		}

		@Override
		public void run() {
			try {
				File postionfile = new File("/mnt/sdcard/" + threadid + ".txt");
				URL url = new URL(filepath);
				HttpURLConnection conn = (HttpURLConnection) url
						.openConnection();
				System.out.println("线程" + threadid + "正在下载 " + "开始位置 : "
						+ startposition + "结束位置 " + endpositon);

				if (postionfile.exists()) {
					FileInputStream fis = new FileInputStream(postionfile);
					byte[] result = StreamTool.getBytes(fis);
					String str = new String(result);
					if (!"".equals(str)) {
						int newstartposition = Integer.parseInt(str);
						if (newstartposition > startposition) {
							startposition = newstartposition;
						}
					}
				}

				// "Range", "bytes=2097152-4194303")
				conn.setRequestProperty("Range", "bytes=" + startposition + "-"
						+ endpositon);
				conn.setRequestMethod("GET");
				conn.setConnectTimeout(5000);
				conn.setRequestProperty("User-Agent",
						"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
				InputStream is = conn.getInputStream();
				RandomAccessFile file = new RandomAccessFile("/mnt/sdcard/"
						+ getFilenName(filepath), "rwd");
				// 设置 数据从文件哪个位置开始写
				file.seek(startposition);
				byte[] buffer = new byte[1024];
				int len = 0;
				// 代表当前读到的服务器数据的位置 ,同时这个值已经存储的文件的位置
				int currentPostion = startposition;
				// 创建一个文件对象 ,记录当前某个文件的下载位置

				while ((len = is.read(buffer)) != -1) {
					if (stopflag) {
						return;
					}
					file.write(buffer, 0, len);

					synchronized (DemoActivity.this) {
						total += len;
					}

					currentPostion += len;
					// 需要把currentPostion 信息给持久化到存储设备
					String position = currentPostion + "";
					FileOutputStream fos = new FileOutputStream(postionfile);
					fos.write(position.getBytes());
					fos.flush();
					fos.close();
				}

				file.close();
				System.out.println("线程" + threadid + "下载完毕");
				// 当线程下载完毕后 把文件删除掉
				if (postionfile.exists()) {
					postionfile.delete();
				}

			} catch (Exception e) {
				e.printStackTrace();
			}

			super.run();
		}

	}

	public String getFilenName(String path) {
		int start = path.lastIndexOf("/") + 1;
		return path.substring(start, path.length());
	}
}

package cn.itcast.mutiledownload;

import java.io.ByteArrayOutputStream;
import java.io.InputStream;

public class StreamTool {
	/**
	 * 把一个inputstream里面的内容转化成一个byte[] 
	 */
	
	public static byte[] getBytes(InputStream is) throws Exception{
		ByteArrayOutputStream bos = new ByteArrayOutputStream();
		byte[] buffer = new byte[1024];
		int len = 0;
		while((len = is.read(buffer))!=-1){
			bos.write(buffer, 0, len);
		}
		is.close();
		bos.flush();
		byte[] result = bos.toByteArray();
		System.out.println(new String(result));
		return  result;
	}
}