Android 断点续传下载

以前一直对断点续传之类的心存困惑，后来有时间看了看传智播客的视频，通过视频的讲解终于解开了我心中的困惑。下面就具体的看看实现的代码，代码中已经给出了详细的注释，相信读者一定看的懂的。

1：断点续传下载，其中会看到“续传”两个字，当然续传的话需要用到存储，这里采用的是Android中的SQLite数据库，要在Android数据库中创建自己的表格需要继承Android中的SQLiteOpenHelper类，这个类中通过重写onCreate()和onUpgrade()方法可以实现表格的创建，删除，更新等一系列的操作。

package cn.itcast.service;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;//用于创建数据库的类public class DBOpenHelper extends SQLiteOpenHelper {private static final String DBNAME = "itcast.db";//数据库名称private static final int VERSION = 1;//数据库版本public DBOpenHelper(Context context) {//构造器，上下文对象，数据库名称，游标（传入null，会调用系统默认的游标，数据库版本）super(context, DBNAME, null, VERSION);}@Overridepublic void onCreate(SQLiteDatabase db) {//创建数据库表格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) {//数据库升级时会用到，通过传入新的版本号来进行升级db.execSQL("DROP TABLE IF EXISTS filedownlog");onCreate(db);}}

2：创建完毕表格后，接下来的工作就是在下载之前需要从数据库加载每条线程已经下载的数据长度，只有这样我们才可以实现“续传”这个字眼。当然还要在每条线程的下载过程中实时的更新数据库，当下载完毕后并且中间没有出现异常，需要从数据库中移除相应的记录。接下来给出该工具类的源代码。

package cn.itcast.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) {//创建数据库对象openHelper = new DBOpenHelper(context);}/** * 获取每条线程已经下载的文件长度,Map<Integer,Integer>第一个参数为线程id，第二个参数为已经下载的长度 * @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//得到数据库写对象SQLiteDatabase db = openHelper.getWritableDatabase();//开启一个事务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()});}//执行完毕后设置事务执行成功db.setTransactionSuccessful();}finally{//最后结束事务，如果中间出现问题，由于没有设置事务成功，会自动进行回滚db.endTransaction();}db.close();}/** * 实时更新每条线程已经下载的文件长度,要开启一个事务更新，避免中间出现问题时事务的回滚 * @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();}}

3：有关数据库的类开发完毕后，接下来就真正到了逻辑的开发了，大家先不用去管单个线程类的实现，先理解FileDownloader类的整体的思想，通过客户端传入的下载地址来构建URL，从而得到HttpURLConnection来得到下载文件的大小，再根据下载的线程数来计算每个线程应该下载的文件的长度，以及文件的下载位置，这样线程就可以将一个文件分为多个部分同时进行下载，速度当然会快很多。

package cn.itcast.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 cn.itcast.service.FileService;import android.content.Context;import android.util.Log;/** * 文件下载器 * 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;//上下文对象private FileService fileService;//数据库操作对象private int downloadSize = 0;//已下载文件长度private int fileSize = 0;//原始文件长度 private DownloadThread[] threads;//线程数 private File saveFile;//本地保存文件//缓存各线程下载的长度,支持并发的类private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>();private int block;//每条线程应该下载的长度 private String downloadUrl;//下载路径//获取线程数public int getThreadSize() {return threads.length;}//获取文件大小public int getFileSize() {return fileSize;}//累计已下载大小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) {//key值一样的话，会更新该key值的valuethis.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;//上下文this.downloadUrl = downloadUrl;//文件下载路径fileService = new FileService(this.context);//创建数据库操作对象URL url = new URL(this.downloadUrl);//通过路径创建URL对象if(!fileSaveDir.exists()) fileSaveDir.mkdirs();//创建文件目录this.threads = new DownloadThread[threadNum];//创建线程数组//通过URL打开下载连接HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setConnectTimeout(5*1000);//设置延时时间conn.setRequestMethod("GET");//设置请求方式//下面这些设置可以不写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();//建立连接printResponseHeader(conn);//打印if (conn.getResponseCode()==200) {//如果连接成功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())//把各条线程已经下载的数据长度放入data中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);}//计算每条线程应该下载的数据长度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) {//截取字符串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 {//随机访问文件类RandomAccessFile randOut = new RandomAccessFile(this.saveFile, "rw");if(this.fileSize>0) randOut.setLength(this.fileSize);//设置文件的大小randOut.close();//关闭文件URL url = new URL(this.downloadUrl);//生成URL//如果数据库中的下载记录条数和线程数目不一致if(this.data.size() != this.threads.length){this.data.clear();//清空Mapfor (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);//线程已经下载的数据长度//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){//创建下载线程this.threads[i] = new DownloadThread(this, url, this.saveFile, this.block, this.data.get(i+1), i+1);this.threads[i].setPriority(7);//设置线程的优先级，可以不设置this.threads[i].start();//开启线程去下载}else{//如果本条线程已经下载完毕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);}}

4：下载的大管家开发完毕之后，接下来给出的线程下载类DownloadThread，这个类中就各司其职，从指定的位置下载指定的长度就ok了。

package cn.itcast.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;//下载地址this.saveFile = saveFile;//本地文件保存地址this.block = block;//每条线程应该下载的数据的长度this.downloader = downloader;//引用this.threadId = threadId;//本条线程的idthis.downLength = downLength;//已经下载的数据的长度}@Overridepublic 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;}}

5：下载过程中需要更新进度，这里给出一个回调接口。

package cn.itcast.net.download;public interface DownloadProgressListener {public void onDownloadSize(int size);}

6：下面给出界面类，通过handler来实时的更新进度的显示。

package cn.itcast.download;import java.io.File;import cn.itcast.net.download.DownloadProgressListener;import cn.itcast.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 DownloadActivity 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(){@Overridepublic 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(DownloadActivity.this, R.string.success, 1).show();}break;case -1:Toast.makeText(DownloadActivity.this, R.string.error, 1).show();break;}}    };        @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) {String path = downloadpathText.getText().toString();if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){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    //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    private void download(final String path, final File savedir) {    new Thread(new Runnable() {@Overridepublic void run() {FileDownloader loader = new FileDownloader(DownloadActivity.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() {@Overridepublic 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();}}

7：界面类的配置文件。

<?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/downloadpath"    />        <EditText      android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:text="http://zhangmenshiting.baidu.com/data2/music/118439720/11794803954000128.mp3?xcode=6198868ce597760b6bddb6b921b3dfeb4b2090e8393bf799"    android:id="@+id/downloadpath"    />    <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>

以上就是我对这些代码的理解，算是基本明白了。下载地址是一首音乐，哈哈，陈奕迅的。

下载地址是：http://download.csdn.net/detail/ly985557461/7273281