android开发分享Android实现多线程断点下载的方法

  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());     }   }