断点续传下载器

传智播客的黎活明老师讲了一个断点续传的下载器案例，觉得挺实用的。搞Java开发的其实很多时候并不需要知道代码实现的每一个细节，学会使用别人已经封装好的功能，正是面向对象编程思想的精髓所在。当然，知其然并知其所以然，那最好不过。个人觉得，在精力允许的前提下，才去“知其所以然”才是值得的。好了，言归正传，现在将黎大师封装好的代码一一贴出：

1）下载线程类

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;this.saveFile = saveFile;this.block = block;this.downloader = downloader;this.threadId = threadId;this.downLength = downLength;}@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 (!downloader.getExit() && (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;}}

2、最重要的一个类：文件下载器，开发者只需要面向这个类编程即可实现断点续传下载功能

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 *  */public class FileDownloader {private static final String TAG = "FileDownloader";private Context context;private FileService fileService;/* 停止下载 */private boolean exit;/* 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;}/** * 退出下载 */public void exit(){this.exit = true;}public boolean getExit(){return this.exit;}/** * 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, threadId, pos);}/** * 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总长度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){//如果原先未曾下载或者原先的下载线程数与现在的线程数不一致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}this.downloadSize = 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;}}fileService.delete(this.downloadUrl);//如果存在下载记录，删除它们，然后重新添加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}if(downloadSize == this.fileSize) fileService.delete(this.downloadUrl);//下载完成删除记录} catch (Exception e) {print(e.toString());throw new Exception("file download error");}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);}}

3、进度更新接口

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

4、数据库帮助类，使用过SQLite的都知道

package cn.itcast.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 = "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);}}

5、业务类，完成数据库的增删改查操作

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) {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, int threadId, int pos){SQLiteDatabase db = openHelper.getWritableDatabase();db.execSQL("update filedownlog set downlength=? where downpath=? and threadid=?",new Object[]{pos, path, threadId});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();}}

最后，将其用法也贴出来，其实很简单：

try {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                 loader.exit();//退出下载loader.download(new DownloadProgressListener(){public void onDownloadSize(int size) {print("已经下载："+ size);}});} catch (Exception e) {e.printStackTrace();}

在项目中有需要就可以直接拿来用，非常方便。