Android实现多线程断点下载的方法

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：

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。