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0downloadProgressBar.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-1InputStream 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truethis.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。