Android进阶：实现多线程下载文件

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>

 

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();
             }

         }
     }
 }

 

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;
     }
 }

 

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>