Android实现多线程下载文件的方法

本文实例讲述了android实现多线程下载文件的方法。分享给大家供大家参考。具体如下：

多线程下载大概思路就是通过range 属性实现文件分段，然后用randomaccessfile 来读写文件，最终合并为一个文件

首先看下效果图：

创建工程 threaddemo

首先布局文件 threaddemo.xml

<?xml version="1.0" encoding="utf-8"?> 
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" 
  android:orientation="vertical" 
  android:layout_width="fill_parent" 
  android:layout_height="fill_parent" 
  > 
<textview  
  android:layout_width="fill_parent"  
  android:layout_height="wrap_content"  
  android:text="下载地址" 
  /> 
<textview 
  android:id="@+id/downloadurl" 
  android:layout_width="fill_parent"  
  android:layout_height="wrap_content"  
  android:lines="5" 
  /> 
<textview  
  android:layout_width="fill_parent"  
  android:layout_height="wrap_content"  
  android:text="线程数" 
  /> 
<edittext 
  android:id="@+id/downloadnum" 
  android:layout_width="fill_parent"  
  android:layout_height="wrap_content"  
  /> 
<progressbar 
  android:id="@+id/downloadprogressbar" 
  android:layout_width="fill_parent"  
  style="?android:attr/progressbarstylehorizontal" 
  android:layout_height="wrap_content"  
  /> 
<textview 
  android:id="@+id/downloadinfo" 
  android:layout_width="fill_parent"  
  android:layout_height="wrap_content"  
  android:text="下载进度 0" 
  /> 
<button 
  android:id="@+id/downloadbutton" 
  android:layout_width="wrap_content"  
  android:layout_height="wrap_content"  
  android:text="开始下载" 
  /> 
</linearlayout>

<?xml version="1.0" encoding="utf-8"?>
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android"  android:orientation="vertical" android:layout_width="fill_parent"  android:layout_height="fill_parent"  >
<textview   android:layout_width="fill_parent"   android:layout_height="wrap_content" android:text="下载地址"  />
<textviewandroid:id="@+id/downloadurl"android:layout_width="fill_parent" android:layout_height="wrap_content" android:lines="5"/>
<textview   android:layout_width="fill_parent"   android:layout_height="wrap_content" android:text="线程数"  />
<edittextandroid:id="@+id/downloadnum"android:layout_width="fill_parent" android:layout_height="wrap_content" />
<progressbarandroid:id="@+id/downloadprogressbar"android:layout_width="fill_parent" style="?android:attr/progressbarstylehorizontal"  android:layout_height="wrap_content" />
<textviewandroid:id="@+id/downloadinfo"android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="下载进度 0"/>
<buttonandroid:id="@+id/downloadbutton"android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="开始下载"/>
</linearlayout> 

主界面 acitivity

public class threaddownloaddemo extends activity { 
  private textview downloadurl; 
  private edittext downloadnum; 
  private button downloadbutton; 
  private progressbar downloadprogressbar; 
  private textview downloadinfo; 
  private int downloadedsize = 0; 
  private int filesize = 0; 
  private long downloadtime; 
  @override 
  public void oncreate(bundle savedinstancestate) { 
    super.oncreate(savedinstancestate); 
    setcontentview(r.layout.threaddemo); 
    downloadurl = (textview) findviewbyid(r.id.downloadurl); 
    downloadurl.settext("http://file16.top100.cn/201105110911/aa5cc27cbe34deb50a194581d1300881/special_323149/%e8%8d%b7%e5%a1%98%e6%9c%88%e8%89%b2.mp3"); 
    downloadnum = (edittext) findviewbyid(r.id.downloadnum); 
    downloadinfo = (textview) findviewbyid(r.id.downloadinfo); 
    downloadbutton = (button) findviewbyid(r.id.downloadbutton); 
    downloadprogressbar = (progressbar) findviewbyid(r.id.downloadprogressbar); 
    downloadprogressbar.setvisibility(view.visible); 
    downloadprogressbar.setmax(100); 
    downloadprogressbar.setprogress(0); 
    downloadbutton.setonclicklistener(new onclicklistener() { 
      public void onclick(view v) { 
        download(); 
        downloadtime = systemclock.currentthreadtimemillis(); 
      } 
    }); 
  } 
  private void download() { 
    // 获取sd卡目录  
    string dowloaddir = environment.getexternalstoragedirectory() 
        + "/threaddemodownload/"; 
    file file = new file(dowloaddir); 
    //创建下载目录  
    if (!file.exists()) { 
      file.mkdirs(); 
    } 
    //读取下载线程数，如果为空，则单线程下载  
    int downloadtn = integer.valueof("".equals(downloadnum.gettext() 
        .tostring()) ? "1" : downloadnum.gettext().tostring()); 
    string filename = "hetang.mp3"; 
    //开始下载前把下载按钮设置为不可用  
    downloadbutton.setclickable(false); 
    //进度条设为0  
    downloadprogressbar.setprogress(0); 
    //启动文件下载线程  
    new downloadtask("http://file16.top100.cn/201105110911/aa5cc27cbe34deb50a194581d1300881/special_323149/%e8%8d%b7%e5%a1%98%e6%9c%88%e8%89%b2.mp3", integer 
        .valueof(downloadtn), dowloaddir + filename).start(); 
  } 
  handler handler = new handler() { 
    @override 
    public void handlemessage(message msg) { 
      //当收到更新视图消息时，计算已完成下载百分比，同时更新进度条信息  
      int progress = (double.valueof((downloadedsize * 1.0 / filesize * 100))).intvalue(); 
      if (progress == 100) { 
        downloadbutton.setclickable(true); 
        downloadinfo.settext("下载完成！"); 
        dialog mdialog = new alertdialog.builder(threaddownloaddemo.this) 
          .settitle("提示信息") 
          .setmessage("下载完成，总用时为:"+(systemclock.currentthreadtimemillis()-downloadtime)+"毫秒") 
          .setnegativebutton("确定", new dialoginterface.onclicklistener(){ 
            @override 
            public void onclick(dialoginterface dialog, int which) { 
              dialog.dismiss(); 
            } 
          }) 
          .create(); 
        mdialog.show(); 
      } else { 
        downloadinfo.settext("当前进度:" + progress + "%"); 
      } 
      downloadprogressbar.setprogress(progress); 
    } 
  }; 
  public class downloadtask extends thread { 
    private int blocksize, downloadsizemore; 
    private int threadnum = 5; 
    string urlstr, threadno, filename; 
    public downloadtask(string urlstr, int threadnum, string filename) { 
      this.urlstr = urlstr; 
      this.threadnum = threadnum; 
      this.filename = filename; 
    } 
    @override 
    public void run() { 
      filedownloadthread[] fds = new filedownloadthread[threadnum]; 
      try { 
        url url = new url(urlstr); 
        urlconnection conn = url.openconnection(); 
        //防止返回-1  
        inputstream in = conn.getinputstream(); 
        //获取下载文件的总大小  
        filesize = conn.getcontentlength(); 
        log.i("bb", "======================filesize:"+filesize); 
        //计算每个线程要下载的数据量  
        blocksize = filesize / threadnum; 
        // 解决整除后百分比计算误差  
        downloadsizemore = (filesize % threadnum); 
        file file = new file(filename); 
        for (int i = 0; i < threadnum; i++) { 
          log.i("bb", "======================i:"+i); 
          //启动线程，分别下载自己需要下载的部分  
          filedownloadthread fdt = new filedownloadthread(url, file, i * blocksize, (i + 1) * blocksize - 1); 
          fdt.setname("thread" + i); 
          fdt.start(); 
          fds[i] = fdt; 
        } 
        boolean finished = false; 
        while (!finished) { 
          // 先把整除的余数搞定  
          downloadedsize = downloadsizemore; 
          finished = true; 
          for (int i = 0; i < fds.length; i++) { 
            downloadedsize += fds[i].getdownloadsize(); 
            if (!fds[i].isfinished()) { 
              finished = false; 
            } 
          } 
          handler.sendemptymessage(0); 
          //线程暂停一秒  
          sleep(1000); 
        } 
      } catch (exception e) { 
        e.printstacktrace(); 
      } 
    } 
  } 
} 
public class threaddownloaddemo extends activity {
private textview downloadurl;
private edittext downloadnum;
private button downloadbutton;
private progressbar downloadprogressbar;
private textview downloadinfo;
private int downloadedsize = 0;
private int filesize = 0;
private long downloadtime;
@overridepublic void oncreate(bundle savedinstancestate) {
super.oncreate(savedinstancestate);
setcontentview(r.layout.threaddemo);
downloadurl = (textview) findviewbyid(r.id.downloadurl);
downloadurl.settext("http://file16.top100.cn/201105110911/aa5cc27cbe34deb50a194581d1300881/special_323149/%e8%8d%b7%e5%a1%98%e6%9c%88%e8%89%b2.mp3");
downloadnum = (edittext) findviewbyid(r.id.downloadnum);
downloadinfo = (textview) findviewbyid(r.id.downloadinfo);
downloadbutton = (button) findviewbyid(r.id.downloadbutton);
downloadprogressbar = (progressbar) findviewbyid(r.id.downloadprogressbar);
downloadprogressbar.setvisibility(view.visible);
downloadprogressbar.setmax(100);
downloadprogressbar.setprogress(0);
downloadbutton.setonclicklistener(new onclicklistener() {
public void onclick(view v) {download();
downloadtime = systemclock.currentthreadtimemillis();
}
}
);
}
private void download() {// 获取sd卡目录
string dowloaddir = environment.getexternalstoragedirectory()+ "/threaddemodownload/";
file file = new file(dowloaddir);
//创建下载目录
if (!file.exists()) {file.mkdirs();
}//读取下载线程数，如果为空，则单线程下载
int downloadtn = integer.valueof("".equals(downloadnum.gettext().tostring()) ? "1" : downloadnum.gettext().tostring());
string filename = "hetang.mp3";
//开始下载前把下载按钮设置为不可用
downloadbutton.setclickable(false);
//进度条设为0
downloadprogressbar.setprogress(0);
//启动文件下载线程
new downloadtask("http://file16.top100.cn/201105110911/aa5cc27cbe34deb50a194581d1300881/special_323149/%e8%8d%b7%e5%a1%98%e6%9c%88%e8%89%b2.mp3", integer.valueof(downloadtn), dowloaddir + filename).start();
}
handler handler = new handler() {@overridepublic void handlemessage(message msg) {
//当收到更新视图消息时，计算已完成下载百分比，同时更新进度条信息
int progress = (double.valueof((downloadedsize * 1.0 / filesize * 100))).intvalue();
if (progress == 100) {downloadbutton.setclickable(true);
downloadinfo.settext("下载完成！");
dialog mdialog = new alertdialog.builder(threaddownloaddemo.this).settitle("提示信息").setmessage("下载完成，总用时为:"+(systemclock.currentthreadtimemillis()-downloadtime)+"毫秒").setnegativebutton("确定", new dialoginterface.onclicklistener(){@overridepublic void onclick(dialoginterface dialog, int which) {dialog.dismiss();
}}).create();
mdialog.show();
} else {
downloadinfo.settext("当前进度:" + progress + "%");
}
downloadprogressbar.setprogress(progress);
}
}; 
public class downloadtask extends thread {private int blocksize, downloadsizemore;
private int threadnum = 5;
string urlstr, threadno, filename;
public downloadtask(string urlstr, int threadnum, string filename) {
this.urlstr = urlstr;
this.threadnum = threadnum;
this.filename = filename;
}
@overridepublic void run() {
filedownloadthread[] fds = new filedownloadthread[threadnum];
try {url url = new url(urlstr);
urlconnection conn = url.openconnection();
//防止返回-1
inputstream in = conn.getinputstream();
//获取下载文件的总大小
filesize = conn.getcontentlength();
log.i("bb", "======================filesize:"+filesize);
//计算每个线程要下载的数据量
blocksize = filesize / threadnum;
// 解决整除后百分比计算误差
downloadsizemore = (filesize % threadnum);
file file = new file(filename);
for (int i = 0; i < threadnum; i++) {
log.i("bb", "======================i:"+i);
//启动线程，分别下载自己需要下载的部分
filedownloadthread fdt = new filedownloadthread(url, file, i * blocksize, (i + 1) * blocksize - 1);
fdt.setname("thread" + i);
fdt.start();
fds[i] = fdt;
}
boolean finished = false;
while (!finished) {
// 先把整除的余数搞定
downloadedsize = downloadsizemore;
finished = true;
for (int i = 0; i < fds.length; i++) {
downloadedsize += fds[i].getdownloadsize();
if (!fds[i].isfinished()) {
finished = false;
}
}
handler.sendemptymessage(0);
//线程暂停一秒sleep(1000);
}
}
catch (exception e) {
e.printstacktrace();
}
}
}
} 

这里启动线程将文件分割为几个部分，每一个部分再启动一个线程去下载数据
下载文件的线程

public class filedownloadthread extends thread{ 
  private static final int buffer_size=1024; 
  private url url; 
  private file file; 
  private int startposition; 
  private int endposition; 
  private int curposition; 
  //标识当前线程是否下载完成  
  private boolean finished=false; 
  private int downloadsize=0; 
  public filedownloadthread(url url,file file,int startposition,int endposition){ 
    this.url=url; 
    this.file=file; 
    this.startposition=startposition; 
    this.curposition=startposition; 
    this.endposition=endposition; 
  } 
  @override 
  public void run() { 
    bufferedinputstream bis = null; 
    randomaccessfile fos = null;                         
    byte[] buf = new byte[buffer_size]; 
    urlconnection con = null; 
    try { 
      con = url.openconnection(); 
      con.setallowuserinteraction(true); 
      //设置当前线程下载的起止点  
      con.setrequestproperty("range", "bytes=" + startposition + "-" + endposition); 
      log.i("bb", thread.currentthread().getname()+" bytes=" + startposition + "-" + endposition); 
      //使用java中的randomaccessfile 对文件进行随机读写操作  
      fos = new randomaccessfile(file, "rw"); 
      //设置写文件的起始位置  
      fos.seek(startposition); 
      bis = new bufferedinputstream(con.getinputstream());  
      //开始循环以流的形式读写文件  
      while (curposition < endposition) { 
        int len = bis.read(buf, 0, buffer_size);         
        if (len == -1) { 
          break; 
        } 
        fos.write(buf, 0, len); 
        curposition = curposition + len; 
        if (curposition > endposition) { 
          downloadsize+=len - (curposition - endposition) + 1; 
        } else { 
          downloadsize+=len; 
        } 
      } 
      //下载完成设为true  
      this.finished = true; 
      bis.close(); 
      fos.close(); 
    } catch (ioexception e) { 
      e.printstacktrace(); 
    } 
  } 
  public boolean isfinished(){ 
    return finished; 
  } 
  public int getdownloadsize() { 
    return downloadsize; 
  } 
} 
public class filedownloadthread extends thread{
private static final int buffer_size=1024;
private url url;
private file file;
private int startposition;
private int endposition;
private int curposition;//标识当前线程是否下载完成
private boolean finished=false;
private int downloadsize=0;
public filedownloadthread(url url,file file,int startposition,int endposition){
this.url=url;
this.file=file;
this.startposition=startposition;
this.curposition=startposition;
this.endposition=endposition;
}
@overridepublic void run() {
bufferedinputstream bis = null;
randomaccessfile fos = null;
byte[] buf = new byte[buffer_size];
urlconnection con = null;
try {
con = url.openconnection();
con.setallowuserinteraction(true);
//设置当前线程下载的起止点
con.setrequestproperty("range", "bytes=" + startposition + "-" + endposition);
log.i("bb", thread.currentthread().getname()+" bytes=" + startposition + "-" + endposition);
//使用java中的randomaccessfile 对文件进行随机读写操作
fos = new randomaccessfile(file, "rw");
//设置写文件的起始位置
fos.seek(startposition);
bis = new bufferedinputstream(con.getinputstream());
//开始循环以流的形式读写文件
while (curposition < endposition) {
int len = bis.read(buf, 0, buffer_size);
if (len == -1) {
break;
}
fos.write(buf, 0, len);
curposition = curposition + len;
if (curposition > endposition) {
downloadsize+=len - (curposition - endposition) + 1;
} else {
downloadsize+=len;
}
}
//下载完成设为true
this.finished = true;
bis.close();
fos.close();
} catch (ioexception e) {
e.printstacktrace();
}
}
public boolean isfinished(){return finished;}
public int getdownloadsize() {return downloadsize;}
}

这里通过randomaccessfile 的seek方法定位到相应的位置 并实时记录下载量
当然这里需要联网和访问sd卡 所以要加上相应的权限

<uses-permission android:name="android.permission.internet" /> 
<uses-permission android:name="android.permission.write_external_storage"></uses-permission> 
<uses-permission android:name="android.permission.internet" /><uses-permission android:name="android.permission.write_external_storage"></uses-permission>

这样就ok了 下面可以看看断点续传的问题了。有待测试~~

希望本文所述对大家的android程序设计有所帮助。