本文实例讲述了Android实现多线程断点下载的方法。分享给大家供大家参考。具体实现方法如下：
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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() { @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 (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()); } } |
希望本文所述对大家的Android程序设计有所帮助。
