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id public DownloadThread(URL url, File saveFile, int block, int threadid) { this.url = url; this.saveFile = saveFile; this.block = block; this.threadid = threadid; } @Override public 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() { @Override public 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() { @Override public 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 */ @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(); //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 @Override public 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; } @Override public 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0 this.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); } @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); } }

/** * 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 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(); } }