Android 多线程断点下载的实现方法

来源：互联网发布：淘宝返现最多的app 编辑：程序博客网时间：2024/04/29 02:02
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 extendsActivity implementsOnClickListener {  
  privateProgressBar pb;  
  privateButton bt;  
  privateTextView tv;  
  privateEditText et;  
  booleanflag = true; 
  booleanstopflag = false; 
  privateHandler handler = newHandler() {  
    @Override 
    publicvoid handleMessage(Message msg) { 
      pb.setProgress(total); 
      intmax = pb.getMax();  
      if(total >= (max - 1)) { 
        total = max; 
        flag =false;  
      } 
      intresult = total * 100/ max;  
      tv.setText("当前进度 :"+ result + "%"); 
      super.handleMessage(msg); 
    } 
  }; 
  inttotal = 0; 
  @Override 
  publicvoid 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 
  publicvoid onClick(View v) { 
    switch(v.getId()) {  
    caseR.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;  
      } 
        newThread() {  
          @Override 
          publicvoid 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)"); 
          intcode = conn.getResponseCode();  
          if(code == 200) { 
            intlen = 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 
            intthreadnumber = 3; 
            intblocksize = 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++) { 
              intstartposition = i * blocksize;  
              intendpositon = (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; 
    } 
  } 
  classDownLoadTask extendsThread {  
    intthreadid;  
    String filepath; 
    intstartposition;  
    intendpositon;  
    publicDownLoadTask(intthreadid, String filepath, intstartposition,  
        intendpositon) {  
      this.threadid = threadid; 
      this.filepath = filepath; 
      this.startposition = startposition; 
      this.endpositon = endpositon; 
    } 
    @Override 
    publicvoid 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)) { 
            intnewstartposition = 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]; 
        intlen = 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 
        intcurrentPostion = 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(); 
    } 
  } 
  publicString getFilenName(String path) {  
    intstart = path.lastIndexOf("/") +1;  
    returnpath.substring(start, path.length());  
  } 
}
希望本文所述对大家的Android程序设计有所帮助。
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