本示例介绍在Android平台下通过HTTP协议实现断点续传下载。
我们编写的是Andorid的HTTP协议多线程断点下载应用程序。直接使用单线程下载HTTP文件对我们来说是一件非常简单的事。那么,多线程断点需要什么功能?难在哪里?
1.多线程下载,
2.支持断点。
使用多线程的好处:使用多线程下载会提升文件下载的速度。那么多线程下载文件的过程是:
(1)首先获得下载文件的长度,然后设置本地文件的长度。
HttpURLConnection.getContentLength();//获取下载文件的长度
RandomAccessFile file = new RandomAccessFile("QQWubiSetup.exe","rwd");
file.setLength(filesize);//设置本地文件的长度
(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。
如:文件的长度为6M,线程数为3,那么,每条线程下载的数据长度为2M,每条线程开始下载的位置如下图所示。
例如10M大小,使用3个线程来下载,
线程下载的数据长度 (10%3 == 0 ? 10/3:10/3+1) ,第1,2个线程下载长度是4M,第三个线程下载长度为2M
下载开始位置:线程id*每条线程下载的数据长度 = ?
下载结束位置:(线程id+1)*每条线程下载的数据长度-1=?
(3)使用Http的Range头字段指定每条线程从文件的什么位置开始下载,下载到什么位置为止,
如:指定从文件的2M位置开始下载,下载到位置(4M-1byte)为止
代码如下:HttpURLConnection.setRequestProperty("Range", "bytes=2097152-4194303");
(4)保存文件,使用RandomAccessFile类指定每条线程从本地文件的什么位置开始写入数据。
RandomAccessFile threadfile = new RandomAccessFile("QQWubiSetup.exe ","rwd");
threadfile.seek(2097152);//从文件的什么位置开始写入数据
程序结构如下图所示:
string.xml文件中代码:
- <?xml version="1.0" encoding="utf-8"?>
- <resources>
- <string name="hello">Hello World, MainActivity!</string>
- <string name="app_name">Android网络多线程断点下载</string>
- <string name="path">下载路径</string>
- <string name="downloadbutton">下载</string>
- <string name="sdcarderror">SDCard不存在或者写保护</string>
- <string name="success">下载完成</string>
- <string name="error">下载失败</string>
- </resources>
main.xml文件中代码:
- <?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">
- <!-- 下载路径 -->
- <TextView
- android:layout_width="fill_parent"
- android:layout_height="wrap_content"
- android:text="@string/path"/>
- <EditText
- android:id="@+id/path"
- android:text="http://www.winrar.com.cn/download/wrar380sc.exe"
- android:layout_width="fill_parent"
- android:layout_height="wrap_content">
- </EditText>
- <!-- 下载按钮 -->
- <Button
- android:layout_width="wrap_content"
- android:layout_height="wrap_content"
- android:text="@string/downloadbutton"
- android:id="@+id/button"/>
- <!-- 进度条 -->
- <ProgressBar
- android:layout_width="fill_parent"
- android:layout_height="20dip"
- 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/resultView" />
- </LinearLayout>
AndroidManifest.xml文件中代码:
- <?xml version="1.0" encoding="utf-8"?>
- <manifest
xmlns:android="http://schemas.android.com/apk/res/android"
package="com.android.downloader" android:versionCode="1"
android:versionName="1.0"> - <uses-sdk android:minSdkVersion="8" />
- <application android:icon="@drawable/icon" android:label="@string/app_name">
- <activity android:name=".MainActivity"
- android:label="@string/app_name">
- <intent-filter>
- <action android:name="android.intent.action.MAIN" />
- <category android:name="android.intent.category.LAUNCHER" />
- </intent-filter>
- </activity>
- </application>
- <!-- 在SDCard中创建与删除文件权限 -->
- <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
- <!-- 往SDCard写入数据权限 -->
- <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
- <!-- 访问internet权限 -->
- <uses-permission android:name="android.permission.INTERNET"/>
- </manifest>
MainActivity中代码:
- package com.android.downloader;
- import java.io.File;
- import com.android.network.DownloadProgressListener;
- import com.android.network.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 downloadpathText;
- private TextView resultView;
- private ProgressBar progressBar;
- /**
- * 当Handler被创建会关联到创建它的当前线程的消息队列,该类用于往消息队列发送消息
- * 消息队列中的消息由当前线程内部进行处理
- */
- private Handler handler = new Handler(){
- @Override
- public void handleMessage(Message msg) {
- switch (msg.what) {
- case 1:
- progressBar.setProgress(msg.getData().getInt("size"));
- float num = (float)progressBar.getProgress()/(float)progressBar.getMax();
- int result = (int)(num*100);
- resultView.setText(result+ "%");
- if(progressBar.getProgress()==progressBar.getMax()){
- Toast.makeText(MainActivity.this, R.string.success, 1).show();
- }
- break;
- case -1:
- Toast.makeText(MainActivity.this, R.string.error, 1).show();
- break;
- }
- }
- };
- /** Called when the activity is first created. */
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- downloadpathText = (EditText) this.findViewById(R.id.path);
- progressBar = (ProgressBar) this.findViewById(R.id.downloadbar);
- resultView = (TextView) this.findViewById(R.id.resultView);
- Button button = (Button) this.findViewById(R.id.button);
- button.setOnClickListener(new View.OnClickListener() {
- @Override
- public void onClick(View v) {
- // TODO Auto-generated method stub
- String path = downloadpathText.getText().toString();
- System.out.println(Environment.getExternalStorageState()+"------"+Environment.MEDIA_MOUNTED);
- if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
- download(path, Environment.getExternalStorageDirectory());
- }else{
- Toast.makeText(MainActivity.this, R.string.sdcarderror, 1).show();
- }
- }
- });
- }
- /**
- * 主线程(UI线程)
- * 对于显示控件的界面更新只是由UI线程负责,如果是在非UI线程更新控件的属性值,更新后的显示界面不会反映到屏幕上
- * @param path
- * @param savedir
- */
- private void download(final String path, final File savedir) {
- new Thread(new Runnable() {
- @Override
- public void run() {
- FileDownloader loader = new FileDownloader(MainActivity.this, path, savedir, 3);
- progressBar.setMax(loader.getFileSize());//设置进度条的最大刻度为文件的长度
- try {
- loader.download(new DownloadProgressListener() {
- @Override
- public void onDownloadSize(int size) {//实时获知文件已经下载的数据长度
- Message msg = new Message();
- msg.what = 1;
- msg.getData().putInt("size", size);
- handler.sendMessage(msg);//发送消息
- }
- });
- } catch (Exception e) {
- handler.obtainMessage(-1).sendToTarget();
- }
- }
- }).start();
- }
- }
DBOpenHelper中代码:
- package com.android.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 = "down.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);
- }
- }
FileService中代码:
- package com.android.service;
- import java.util.HashMap;
- import java.util.Map;
- import android.content.Context;
- import android.database.Cursor;
- import android.database.sqlite.SQLiteDatabase;
- 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();
- }
- }
DownloadProgressListener中代码:
- package com.android.network;
- public interface DownloadProgressListener {
- public void onDownloadSize(int size);
- }
FileDownloader中代码:
- package com.android.network;
- 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.android.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
- * @param conn
- * @return
- */
- 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);
- }
- }
DownloadThread 中代码:
- package com.android.network;
- 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;
- }
- }
运行效果如下:
完毕。^_^