多线程断点下载（开始下载，暂停下载，百分比进度条）
package cn.itcast.download;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 cn.itcast.mutiledownload.StreamTool;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 MutiledownloadActivity 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() {@Overridepublic 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;@Overridepublic 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);}@Overridepublic void onClick(View v) {switch (v.getId()) {case R.id.bt:// 创建一个子线程 定期的更新uiif("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() {@Overridepublic 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;}@Overridepublic 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 (MutiledownloadActivity.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());}}