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。