Android下使用Http协议实现多线程断点续传下载

0.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();

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

1.多线程下载的核心代码示例

public class MulThreadDownload {/** * 多线程下载 * @param args */public static void main(String[] args) {String path = "http://net.hoo.com/QQWubiSetup.exe";try {new MulThreadDownload().download(path, 3);}catch (Exception e) {e.printStackTrace();}}/** * 从路径中获取文件名称 * @param path 下载路径 * @return */public static String getFilename(String path){return path.substring(path.lastIndexOf('/')+1);}/** * 下载文件 * @param path 下载路径 * @param threadsize 线程数 */public void download(String path, int threadsize) throws Exception{URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection)url.openConnection();conn.setRequestMethod("GET");conn.setConnectTimeout(5 * 1000);//获取要下载的文件的长度int filelength = conn.getContentLength();//从路径中获取文件名称String filename = getFilename(path);File saveFile = new File(filename);RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");//设置本地文件的长度和下载文件相同accessFile.setLength(filelength);accessFile.close();//计算每条线程下载的数据长度int block = filelength%threadsize==0? filelength/threadsize : filelength/threadsize+1;for(int threadid=0 ; threadid < threadsize ; threadid++){new DownloadThread(url, saveFile, block, threadid).start();}}private final class DownloadThread extends Thread{private URL url;private File saveFile;private int block;//每条线程下载的数据长度private int threadid;//线程idpublic DownloadThread(URL url, File saveFile, int block, int threadid) {this.url = url;this.saveFile = saveFile;this.block = block;this.threadid = threadid;}@Overridepublic void run() {//计算开始位置公式：线程id*每条线程下载的数据长度= ？ //计算结束位置公式：（线程id +1）*每条线程下载的数据长度-1 =?int startposition = threadid * block;int endposition = (threadid + 1 ) * block - 1;try {RandomAccessFile accessFile = new RandomAccessFile(saveFile, "rwd");//设置从什么位置开始写入数据accessFile.seek(startposition);HttpURLConnection conn = (HttpURLConnection)url.openConnection();conn.setRequestMethod("GET");conn.setConnectTimeout(5 * 1000);conn.setRequestProperty("Range", "bytes="+ startposition+ "-"+ endposition);InputStream inStream = conn.getInputStream();byte[] buffer = new byte[1024];int len = 0;while( (len=inStream.read(buffer)) != -1 ){accessFile.write(buffer, 0, len);}inStream.close();accessFile.close();System.out.println("线程id:"+ threadid+ "下载完成");}catch (Exception e) {e.printStackTrace();}}}}

2.多线程断点下载功能，这里把断点数据保存到数据库中：注意代码注释的理解

(0)主Activity，关键点使用Handler更新进度条与开启线程下载避免ANR

若不使用Handler却要立即更新进度条数据，可使用：

//resultView.invalidate(); UI线程中立即更新进度条方法

//resultView.postInvalidate(); 非UI线程中立即更新进度条方法

/** * 注意这里的设计思路，UI线程与参数保存问题，避免ANR问题，UI控件的显示 * @author kay * */public class DownloadActivity extends Activity { private EditText downloadpathText; private TextView resultView; private ProgressBar progressBar; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); downloadpathText = (EditText) this.findViewById(R.id.downloadpath); progressBar = (ProgressBar) this.findViewById(R.id.downloadbar); resultView = (TextView) this.findViewById(R.id.result); Button button = (Button) this.findViewById(R.id.button); button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {//取得下载路径String path = downloadpathText.getText().toString();//判断SDCard是否存在if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){//下载操作download(path, Environment.getExternalStorageDirectory());}else{Toast.makeText(DownloadActivity.this, R.string.sdcarderror, 1).show();}}}); } //主线程(UI线程) //业务逻辑正确，但是该程序运行的时候有问题(可能出现ANR问题) //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 /** * 参数类型：因为启动一个线程还需要使用到上面方法的参数，而主方法启动后很快就会销毁， * 那么使用Final可以解决参数丢失的问题 * path 注意是Final类型 * savedir 注意是Final类型 */ private void download(final String path, final File savedir) { //这里开启一个线程避免ANR错误 new Thread(new Runnable() {@Overridepublic void run() {FileDownloader loader = new FileDownloader(DownloadActivity.this, path, savedir, 3);//设置进度条的最大刻度为文件的长度progressBar.setMax(loader.getFileSize());try {loader.download(new DownloadProgressListener() {/** * 注意这里的设计，显示进度条数据需要使用Handler来处理 * 因为非UI线程更新后的数据不能被刷新 */@Overridepublic void onDownloadSize(int size) {//实时获知文件已经下载的数据长度Message msg = new Message();//设置消息标签msg.what = 1;msg.getData().putInt("size", size);//使用Handler对象发送消息handler.sendMessage(msg);}});}catch (Exception e){//发送一个空消息到消息队列handler.obtainMessage(-1).sendToTarget();/** * 或者使用下面的方法发送一个空消息 * Message msg = new Message(); *msg.what = 1; *handler.sendMessage(msg); */}}}).start();} /**Handler原理：当Handler被创建时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() { //重写Handler里面的handleMessage方法处理消息@Overridepublic void handleMessage(Message msg) {switch (msg.what) {case 1://进度条显示progressBar.setProgress(msg.getData().getInt("size"));float num = (float)progressBar.getProgress()/(float)progressBar.getMax();int result = (int)(num*100);//resultView.invalidate(); UI线程中立即更新进度条方法//resultView.postInvalidate(); 非UI线程中立即更新进度条方法resultView.setText(result+ "%");//判断是否下载成功if(progressBar.getProgress()==progressBar.getMax()){Toast.makeText(DownloadActivity.this, R.string.success, 1).show();}break;case -1:Toast.makeText(DownloadActivity.this, R.string.error, 1).show();break;}} }; }

(1)下载类：

注意计算每条线程的下载长度与下载起始位置的方法

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;//下载文件长度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;}@Overridepublic void run() {//未下载完成if(downLength < block){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");//下载开始位置：线程id*每条线程下载的数据长度 = ?int startPos = block * (threadId - 1) + downLength;//下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?int endPos = block * threadId -1;//设置获取实体数据的范围http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);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");//标记是否完成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;}}

文件下载器，使用

/** * 文件下载器,使用这个类的方法如下示例： * FileDownloader loader = new FileDownloader(context, "http://browse.babasport.com/ejb3/ActivePort.exe", *new File("D://androidsoft//test"), 2); *loader.getFileSize();//得到文件总大小 *try { *loader.download(new DownloadProgressListener(){ *public void onDownloadSize(int size) { *print("已经下载："+ size); *} *}); *} * catch (Exception e) *{ *e.printStackTrace(); *} */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);}/** * 文件下载构造器 * @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) {//根据响应获取文件大小this.fileSize = conn.getContentLength();if (this.fileSize <= 0) throw new RuntimeException("Unkown file size ");//获取文件名称String filename = getFileName(conn);//构建保存文件this.saveFile = new File(fileSaveDir, filename);//获取下载记录Map<Integer, Integer> logdata = fileService.getData(downloadUrl);//如果存在下载记录if(logdata.size()>0){//把各条线程已经下载的数据长度放入data中for(Map.Entry<Integer, Integer> entry : logdata.entrySet())data.put(entry.getKey(), entry.getValue());}//下面计算所有线程已经下载的数据长度if(this.data.size()==this.threads.length){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 {//创建本地文件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++) {//初始化每条线程已经下载的数据长度为0this.data.put(i+1, 0);}}//开启线程进行下载for (int i = 0; i < this.threads.length; i++) {int downLength = this.data.get(i+1);//判断线程是否已经完成下载,否则继续下载if(downLength < this.block && this.downloadSize<this.fileSize){this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);this.threads[i].setPriority(7);//可删除这条this.threads[i].start();}else{this.threads[i] = null;}}this.fileService.save(this.downloadUrl, this.data);//下载未完成boolean notFinish = true;// 循环判断所有线程是否完成下载while (notFinish) {Thread.sleep(900);//假定全部线程下载完成notFinish = false;for (int i = 0; i < this.threads.length; i++){//如果发现线程未完成下载if (this.threads[i] != null && !this.threads[i].isFinish()) {//设置标志为下载没有完成notFinish = true;//如果下载失败,再重新下载if(this.threads[i].getDownLength() == -1){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();}}}//通知目前已经下载完成的数据长度if(listener!=null) listener.onDownloadSize(this.downloadSize);}//删除数据库中下载信息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);}}

public interface DownloadProgressListener {public void onDownloadSize(int size);}

(2)文件操作，断点数据库存储

public class DBOpenHelper extends SQLiteOpenHelper {private static final String DBNAME = "itcast.db";private static final int VERSION = 1;public DBOpenHelper(Context context) {super(context, DBNAME, null, VERSION);}@Overridepublic void onCreate(SQLiteDatabase db) {db.execSQL("CREATE TABLE IF NOT EXISTS filedownlog (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, downlength INTEGER)");}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {db.execSQL("DROP TABLE IF EXISTS filedownlog");onCreate(db);}}

/** * 文件下载业务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 positionSQLiteDatabase 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();}}

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