本文介绍如何在Android应用中实现断点续传功能，通过多线程下载大文件并使用SQLite记录下载状态，确保下载过程的连续性和效率。
当我们从Internet中下载一个文件时，有的文件比较大，比如音乐或视频文件，下载的话需要比较长的时间，当我们在下载过程中，如果手机没电了或者其它原因，使当前的下载中断了，按照一般的程序，当下次下载又需要从新开始，这里我们来实现多纯程断点下载，当下载中断了，下次启动的时候还会接着下载，有点像我们的迅雷了……
首先呢，我们先不急着建Android应用，先建一个Java项目，测试一下下
然后在这个项目里面建一个测试用例
包都可以不填，因为只是测试，不是真正的应用，偷懒了……
OK，接着写代码
package junit.test;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import org.junit.Test;
public class InternetTest {
/**
* 读取输入流并返回数据
* @param input
* @return
* @throws Exception
*/
public byte[] readStream(InputStream input) throws Exception{
byte[] buffer = new byte[1024];
ByteArrayOutputStream output = new ByteArrayOutputStream();
int len = -1;
while((len=input.read(buffer))!=-1){
output.write(buffer, 0, len);
}
input.close();
output.close();
return output.toByteArray();
}
/**
* 从网络上下载图片
* @throws Exception
*/
@Test
public void getImage()throws Exception{
String urlPath = "http://photocdn.sohu.com/20110401/Img280097999.jpg";//在网络上随便找一张图片的链接
URL url = new URL(urlPath);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();//返回一个连接对象
conn.setRequestMethod("GET");//设置请求方式
conn.setConnectTimeout(6*1000);//设置连接超时，这里可以不用设置，但是在android应用中应该设置超时时间
if (conn.getResponseCode()==200) {
InputStream input = conn.getInputStream();
byte[] data = readStream(input);
File file = new File("test.jpg");
FileOutputStream output = new FileOutputStream(file);
output.write(data);
output.close();
}
}
/**
* 得到网页html
* @throws Exception
*/
@Test
public void getHtml()throws Exception{
String urlPath = "http://www.baidu.com";
URL url = new URL(urlPath);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setConnectTimeout(6*1000);
if (conn.getResponseCode()==200) {
InputStream input = conn.getInputStream();
byte[] data = readStream(input);
System.out.println(new String(data));//直接输出到控制台
}
}
}
然后测试，是否有预期的结果，如果有，继续下面，如果没有，再看看是不是哪儿错了
然后再建一个测试类，实现多线程下载，以下载一首mp3为例
package junit.test;
import java.io.ByteArrayOutputStream;
import java.io.File;
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 org.junit.Test;
public class DownloaderTest {
/**
* 读取输入流并返回数据
* @param input
* @return
* @throws Exception
*/
public byte[] readStream(InputStream input) throws Exception {
ByteArrayOutputStream output = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int len = -1;
while ((len = input.read(buffer)) != -1) {
output.write(buffer, 0, len);
}
input.close();
output.close();
return output.toByteArray();
}
@Test
public void downloader() throws Exception {
String urlPath = "http://dl.toofiles.com/vaaoje/audios/qbd.mp3";
URL url = new URL(urlPath);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
int threadsize = 3;//定义线程数
int filesize = conn.getContentLength();// 获取文件大小
int block = filesize / threadsize + 1;// 每条线程下载的数量
conn.disconnect();
File file = new File("千百度.mp3");
RandomAccessFile randfile = new RandomAccessFile(file, "rw");//RandomAccessFile可以指定从文件的什么位置写入数据
for(int i=0;i<threadsize;i++){
int startposition = i * block;//记录每条线程的开始位置
RandomAccessFile threadfile = new RandomAccessFile(file, "rw");
threadfile.seek(startposition);//从文件的什么位置开始写入
new Thread(new DownloadThread(i,url,startposition,threadfile,block)).start();
}
/*
* 设置一个标志，当输入q的时候停止主线程
*/
byte b[] = new byte[1];
System.in.read(b);
while(!('q'==b[0])){
Thread.sleep(3*1000);
}
}
private class DownloadThread implements Runnable{
private int id ;
private URL url;
private int startposition;
private RandomAccessFile threadfile;
private int block;
public DownloadThread(int id ,URL url,int startposition,RandomAccessFile threadfile,int block){
this.id=id;
this.url=url;
this.startposition=startposition;
this.threadfile=threadfile;
this.block=block;
}
@Override
public void run() {
// TODO Auto-generated method stub
try {
HttpURLConnection conn = (HttpURLConnection)url.openConnection();
conn.setRequestMethod("GET");
conn.setRequestProperty("Range", "bytes="+startposition+"-");
conn.setConnectTimeout(6 * 1000);
InputStream input = conn.getInputStream();
byte[] buffer = new byte[1024];
int len = -1;
int readfilesize = 0;//记录下载的文件大小
while (readfilesize<block && ((len = input.read(buffer)) != -1)) {
threadfile.write(buffer, 0, len);
readfilesize += len;//累计下载的文件大小
}
threadfile.close();
conn.disconnect();
System.out.println((this.id+1)+"线程下载完成");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}运行此测试类，如果没有异常抛出的话就成功了……
多线程下载的核心代码已经完成，下面结合到android应用中，我们还得用到SQLite知识，要实现多线程下载，当中断的时候，我们系统会记录一个下载位置，我们把它保存在数据库中，第二次运行的时候再从数据库中读取出来，假设大家都有SQLite方面的知识……
接下来应该建Android项目了
当然如果我们做小一点的Android项目的时候可以先做界面，然后根据需要来扩展所需要的功能，当然有的时候我们宁愿先实现业务，业务功能做好了再实现界面，因为界面里面基本不含有技术，况且我们只是为了学习，界面不需要多美观的，能用就行，OK，继续
先做数据库这层
关于建Android项目方法的截图就省略了，我用的模拟器版本是2.3.3，至今为至最新的吧
首先建一个类DBOpenHelper继续自SQLiteOpenHelper
package com.studio.service; import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper; public class DBOpenHelper extends SQLiteOpenHelper { private static final String DBNAME = "download.db"; private static final int VERSION = 1; public DBOpenHelper(Context context) { super(context, DBNAME, null, VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, downlength INTEGER)"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { db.execSQL("DROP TABLE IF EXISTS filedownlog"); onCreate(db); } }
这里定义的数据名字叫download.db,版本号为1，表名filedownlog,里面有三个字段，一个id,主键，下载路径downpath，线程ID和一个下载长度downlength
然后建一个FileService类
package com.studio.service; import java.util.HashMap; import java.util.Map; import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; /** * 业务bean * */ public class FileService { private DBOpenHelper openHelper; public FileService(Context context) { openHelper = new DBOpenHelper(context); } /** * 获取每条线程已经下载的文件长度 * * @param path * @return */ public Map<Integer, Integer> getData(String path) { SQLiteDatabase db = openHelper.getReadableDatabase(); Cursor cursor = db .rawQuery( "select threadid, downlength from filedownlog where downpath=?", new String[] { path }); Map<Integer, Integer> data = new HashMap<Integer, Integer>(); while (cursor.moveToNext()) { data.put(cursor.getInt(0), cursor.getInt(1)); } cursor.close(); db.close(); return data; } /** * 保存每条线程已经下载的文件长度 * * @param path * @param map */ public void save(String path, Map<Integer, Integer> map) {// int threadid, // int position SQLiteDatabase db = openHelper.getWritableDatabase(); db.beginTransaction(); try { for (Map.Entry<Integer, Integer> entry : map.entrySet()) { db.execSQL( "insert into filedownlog(downpath, threadid, downlength) values(?,?,?)", new Object[] { path, entry.getKey(), entry.getValue() }); } db.setTransactionSuccessful(); } finally { db.endTransaction(); } db.close(); } /** * 实时更新每条线程已经下载的文件长度 * * @param path * @param map */ public void update(String path, Map<Integer, Integer> map) { SQLiteDatabase db = openHelper.getWritableDatabase(); db.beginTransaction(); try { for (Map.Entry<Integer, Integer> entry : map.entrySet()) { db.execSQL( "update filedownlog set downlength=? where downpath=? and threadid=?", new Object[] { entry.getValue(), path, entry.getKey() }); } db.setTransactionSuccessful(); } finally { db.endTransaction(); } db.close(); } /** * 当文件下载完成后，删除对应的下载记录 * * @param path */ public void delete(String path) { SQLiteDatabase db = openHelper.getWritableDatabase(); db.execSQL("delete from filedownlog where downpath=?", new Object[] { path }); db.close(); } }
类中都有相应的注释的，看不懂可以慢慢看……
因为要用到进度条，所以先把进度条建了
package com.studio.net.download; public interface DownloadProgressListener { public void onDownloadSize(int size); }
这里我们定义了一个进度条监听接口，由实现此接口的类来调用onDownloadSize()方法新建一个类DownloadThread继承自Thread
package com.studio.net.download; import java.io.File; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; import android.util.Log; public class DownloadThread extends Thread { private static final String TAG = "DownloadThread"; private File saveFile; private URL downUrl; private int block; /* 下载开始位置 */ private int threadId = -1; private int downLength; private boolean finish = false; private FileDownloader downloader; public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downLength, int threadId) { this.downUrl = downUrl; this.saveFile = saveFile; this.block = block; this.downloader = downloader; this.threadId = threadId; this.downLength = downLength; } @Override public void run() { if (downLength < block) {// 未下载完成 try { HttpURLConnection http = (HttpURLConnection) downUrl .openConnection(); http.setConnectTimeout(5 * 1000); http.setRequestMethod("GET"); http.setRequestProperty( "Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*"); http.setRequestProperty("Accept-Language", "zh-CN"); http.setRequestProperty("Referer", downUrl.toString()); http.setRequestProperty("Charset", "UTF-8"); int startPos = block * (threadId - 1) + downLength;// 开始位置 int endPos = block * threadId - 1;// 结束位置 http.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);// 设置获取实体数据的范围 http.setRequestProperty( "User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)"); http.setRequestProperty("Connection", "Keep-Alive"); InputStream inStream = http.getInputStream(); byte[] buffer = new byte[1024]; int offset = 0; print("Thread " + this.threadId + " start download from position " + startPos); RandomAccessFile threadfile = new RandomAccessFile( this.saveFile, "rwd"); threadfile.seek(startPos); while ((offset = inStream.read(buffer, 0, 1024)) != -1) { threadfile.write(buffer, 0, offset); downLength += offset; downloader.update(this.threadId, downLength); downloader.append(offset); } threadfile.close(); inStream.close(); print("Thread " + this.threadId + " download finish"); this.finish = true; } catch (Exception e) { this.downLength = -1; print("Thread " + this.threadId + ":" + e); } } } private static void print(String msg) { Log.i(TAG, msg); } /** * 下载是否完成 * * @return */ public boolean isFinish() { return finish; } /** * 已经下载的内容大小 * * @return 如果返回值为-1,代表下载失败 */ public long getDownLength() { return downLength; } }
再建一个文件下载器FileDownloader类
package com.studio.net.download; import java.io.File; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.URL; import java.util.LinkedHashMap; import java.util.Map; import java.util.UUID; import java.util.concurrent.ConcurrentHashMap; import java.util.regex.Matcher; import java.util.regex.Pattern; import com.studio.service.FileService; import android.content.Context; import android.util.Log; public class FileDownloader { private static final String TAG = "FileDownloader"; private Context context; private FileService fileService; /* 已下载文件长度 */ private int downloadSize = 0; /* 原始文件长度 */ private int fileSize = 0; /* 线程数 */ private DownloadThread[] threads; /* 本地保存文件 */ private File saveFile; /* 缓存各线程下载的长度 */ private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>(); /* 每条线程下载的长度 */ private int block; /* 下载路径 */ private String downloadUrl; /** * 获取线程数 */ public int getThreadSize() { return threads.length; } /** * 获取文件大小 * * @return */ public int getFileSize() { return fileSize; } /** * 累计已下载大小 * * @param size */ protected synchronized void append(int size) { downloadSize += size; } /** * 更新指定线程最后下载的位置 * * @param threadId * 线程id * @param pos * 最后下载的位置 */ protected synchronized void update(int threadId, int pos) { this.data.put(threadId, pos); this.fileService.update(this.downloadUrl, this.data); } /** * 构建文件下载器 * * @param downloadUrl * 下载路径 * @param fileSaveDir * 文件保存目录 * @param threadNum * 下载线程数 */ public FileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) { try { this.context = context; this.downloadUrl = downloadUrl; fileService = new FileService(this.context); URL url = new URL(this.downloadUrl); if (!fileSaveDir.exists()) fileSaveDir.mkdirs(); this.threads = new DownloadThread[threadNum]; HttpURLConnection conn = (HttpURLConnection) url.openConnection(); conn.setConnectTimeout(5 * 1000); conn.setRequestMethod("GET"); conn.setRequestProperty( "Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, application/x-ms-application, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*"); conn.setRequestProperty("Accept-Language", "zh-CN"); conn.setRequestProperty("Referer", downloadUrl); conn.setRequestProperty("Charset", "UTF-8"); conn.setRequestProperty( "User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)"); conn.setRequestProperty("Connection", "Keep-Alive"); conn.connect(); printResponseHeader(conn); if (conn.getResponseCode() == 200) { this.fileSize = conn.getContentLength();// 根据响应获取文件大小 if (this.fileSize <= 0) throw new RuntimeException("Unkown file size "); String filename = getFileName(conn);// 获取文件名称 this.saveFile = new File(fileSaveDir, filename);// 构建保存文件 Map<Integer, Integer> logdata = fileService .getData(downloadUrl);// 获取下载记录 if (logdata.size() > 0) {// 如果存在下载记录 for (Map.Entry<Integer, Integer> entry : logdata.entrySet()) data.put(entry.getKey(), entry.getValue());// 把各条线程已经下载的数据长度放入data中 } if (this.data.size() == this.threads.length) {// 下面计算所有线程已经下载的数据长度 for (int i = 0; i < this.threads.length; i++) { this.downloadSize += this.data.get(i + 1); } print("已经下载的长度" + this.downloadSize); } // 计算每条线程下载的数据长度 this.block = (this.fileSize % this.threads.length) == 0 ? this.fileSize / this.threads.length : this.fileSize / this.threads.length + 1; } else { throw new RuntimeException("server no response "); } } catch (Exception e) { print(e.toString()); throw new RuntimeException("don't connection this url"); } } /** * 获取文件名 */ private String getFileName(HttpURLConnection conn) { String filename = this.downloadUrl.substring(this.downloadUrl .lastIndexOf('/') + 1); if (filename == null || "".equals(filename.trim())) {// 如果获取不到文件名称 for (int i = 0;; i++) { String mine = conn.getHeaderField(i); if (mine == null) break; if ("content-disposition".equals(conn.getHeaderFieldKey(i) .toLowerCase())) { Matcher m = Pattern.compile(".*filename=(.*)").matcher( mine.toLowerCase()); if (m.find()) return m.group(1); } } filename = UUID.randomUUID() + ".tmp";// 默认取一个文件名 } return filename; } /** * 开始下载文件 * * @param listener * 监听下载数量的变化,如果不需要了解实时下载的数量,可以设置为null * @return 已下载文件大小 * @throws Exception */ public int download(DownloadProgressListener listener) throws Exception { try { RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw"); if (this.fileSize > 0) randOut.setLength(this.fileSize); randOut.close(); URL url = new URL(this.downloadUrl); if (this.data.size() != this.threads.length) { this.data.clear(); for (int i = 0; i < this.threads.length; i++) { this.data.put(i + 1, 0);// 初始化每条线程已经下载的数据长度为0 } } for (int i = 0; i < this.threads.length; i++) {// 开启线程进行下载 int downLength = this.data.get(i + 1); if (downLength < this.block && this.downloadSize < this.fileSize) {// 判断线程是否已经完成下载,否则继续下载 this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i + 1), i + 1); this.threads[i].setPriority(7); this.threads[i].start(); } else { this.threads[i] = null; } } this.fileService.save(this.downloadUrl, this.data); boolean notFinish = true;// 下载未完成 while (notFinish) {// 循环判断所有线程是否完成下载 Thread.sleep(900); notFinish = false;// 假定全部线程下载完成 for (int i = 0; i < this.threads.length; i++) { if (this.threads[i] != null && !this.threads[i].isFinish()) {// 如果发现线程未完成下载 notFinish = true;// 设置标志为下载没有完成 if (this.threads[i].getDownLength() == -1) {// 如果下载失败,再重新下载 this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i + 1), i + 1); this.threads[i].setPriority(7); this.threads[i].start(); } } } if (listener != null) listener.onDownloadSize(this.downloadSize);// 通知目前已经下载完成的数据长度 } fileService.delete(this.downloadUrl); } catch (Exception e) { print(e.toString()); throw new Exception("file download fail"); } return this.downloadSize; } /** * 获取Http响应头字段 * * @param http * @return */ public static Map<String, String> getHttpResponseHeader( HttpURLConnection http) { Map<String, String> header = new LinkedHashMap<String, String>(); for (int i = 0;; i++) { String mine = http.getHeaderField(i); if (mine == null) break; header.put(http.getHeaderFieldKey(i), mine); } return header; } /** * 打印Http头字段 * * @param http */ public static void printResponseHeader(HttpURLConnection http) { Map<String, String> header = getHttpResponseHeader(http); for (Map.Entry<String, String> entry : header.entrySet()) { String key = entry.getKey() != null ? entry.getKey() + ":" : ""; print(key + entry.getValue()); } } private static void print(String msg) { Log.i(TAG, msg); } }
OK至此业务写完了
现在来设计界面UI，由于要使用到String类型的字符串，所以我们先在String.xml中定义一下
添加
<string name="path">下载路径</string> <string name="button">下载</string> <string name="suceess">下载完成</string> <string name="error">下载失败</string> <string name="sdcarderror">SDCard不存在或写保护</string>
界面main.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="@string/path" /> <EditText android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="http://www.mp3upload.ca/upload/42981-fdt.mp3" android:id="@+id/path" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/button" android:id="@+id/button" /> <ProgressBar android:layout_width="fill_parent" android:layout_height="20px" style="?android:attr/progressBarStyleHorizontal" android:id="@+id/downloadbar" /> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center" android:id="@+id/result" /> </LinearLayout>
主类MainActivity
package com.studio.download;
import java.io.File;
import com.studio.net.download.DownloadProgressListener;
import com.studio.net.download.FileDownloader;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
private EditText pathText;
private ProgressBar downloadbar;
private TextView resultView;
// 它用于往消息队列发送消息，当Handler被创建时会自动绑定到Handler被创建时所在的线程所绑定的消息队列
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case 1:
downloadbar.setProgress(msg.getData().getInt("size"));// 把当前已经下载的数据长度设置为进度条的当前刻度
float num = (float) downloadbar.getProgress()
/ (float) downloadbar.getMax();
int result = (int) (num * 100);
resultView.setText(result + "%");
if (downloadbar.getProgress() == downloadbar.getMax()) {
Toast.makeText(MainActivity.this, R.string.suceess, 1)
.show();
}
break;
case -1:
Toast.makeText(MainActivity.this, R.string.error, 1).show();
break;
}
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
pathText = (EditText) findViewById(R.id.path);
downloadbar = (ProgressBar) findViewById(R.id.downloadbar);
resultView = (TextView) findViewById(R.id.result);
Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (Environment.getExternalStorageState().equals(
Environment.MEDIA_MOUNTED)) {
String path = pathText.getText().toString();
download(path, Environment.getExternalStorageDirectory());
} else {
Toast.makeText(MainActivity.this, R.string.sdcarderror, 1)
.show();
}
}
});
}
// 对UI控件的更新只能由主线程(UI线程)负责,如果不在UI线程更新控件，更新后的值不会被重绘到屏幕上
private void download(final String path, final File saveDir) {
new Thread(new Runnable() {
@Override
public void run() {
try {
FileDownloader loader = new FileDownloader(
MainActivity.this, path, saveDir, 3);
downloadbar.setMax(loader.getFileSize());// 设置进度条的最大刻度为文件的大小
loader.download(new DownloadProgressListener() {
@Override
public void onDownloadSize(int size) {
Message msg = new Message();
msg.what = 1;
msg.getData().putInt("size", size);
handler.sendMessage(msg);
// msg.target = handler;
}
});
} catch (Exception e) {
Message msg = new Message();
msg.what = -1;
handler.sendMessage(msg);
}
}
}).start();
}
}
当然别忘了添加权限
<uses-permission android:name="android.permission.INTERNET"></uses-permission> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission> <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"></uses-permission>
OK，搞定，运行一下
如图所示
由于这个mp3有点大，耐心等待
OK，终于下载完成了，看看sdcard吧，上面有我们刚下载的歌曲文件了，播放一下试试
扫一扫
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