Android 多线程、断点续传下载技术1.为什么使用该技术？答：（1）之所以采用多线程下载是因为考虑到手机，及移动设备的cup处理能力，让下载任务多抢占cup资源，从而加快了下载的速度，提高了用户体验（2）断点续传技术，就是在下载过程中如果网络出现问题，导致文件没有下载完，那么下次下载时，接着上次终端位置继续下载，从而减轻了服务器的负担。

2.下面我们就开始建一个多线程下载的项目，来体验多线程下载的优势，项目的结构如下2.1设计UImain.xml代码如下：<?xml version="1.0"encoding="utf-8"?><LinearLayoutxmlns:android="/apk/res /android"android:orientation="vertical"android:layout_width="fill_parent"android:layout_height="fill_parent"><TextViewandroid:layout_width="fill_parent"android:layout_height="wrap_content"android:text="@string/path"/><EditTextandroid:layout_width="fill_parent"android:layout_height="wrap_content"android:text="/kcn/pc/K anbox_10012.exe"android:id="@+id/path"/><Buttonandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="@string/button"android:id="@+id/button"/><ProgressBarandroid:layout_width="fill_parent"android:layout_height="20px"style="?android:attr/progressBarStyleHorizontal"android:id="@+id/downloadbar"/><TextViewandroid:layout_width="fill_parent"android:layout_height="wrap_content"android:gravity="center"android:id="@+id/result"/></LinearLayout>其中引用的string.xml如下：<?xml version="1.0"encoding="utf-8"?><resources><string name="hello">Hello World, SmartDownload!</string><string name="app_name">SMART多线程断点下载器</string><string name="path">下载路径</string><string name="button">下载</string><string name="success">下载完成</string><string name="error">下载失败</string><string name="sdcarderror">SDCard不存在或者写保护</string></resources>3．数据库阶段：3.1编写数据库工具类DBOpenHelerpackage com.smart.db;import android.content.Context;import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper;public class DBOpenHelper extends SQLiteOpenHelper {private static final String DBNAME = "smart.db";private static final int VERSION = 1;public DBOpenHelper(Context context) {super(context, DBNAME, null, VERSION);}@Overridepublic voiddb.execSQL("CREATE TABLE IF NOT EXISTS SmartFileDownlog (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 SmartFileDownlog");onCreate(db);}}3.2对各个线程的下载记录进行数据库的操作，编写Fileservice 类代码如下package com.smart.db;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){openHelper.getReadableDatabase();Cursor cursor = db.rawQuery("select threadid, downlength from SmartFileDownlog where downpath=?", new String[]{path});Map<Integer, Integer> data = newHashMap<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 positionopenHelper.getWritableDatabase();db.beginTransaction();try{for(Map.Entry<Integer, Integer> entry : map.entrySet()){db.execSQL("insert intoSmartFileDownlog(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 SmartFileDownlog 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 SmartFileDownlog where downpath=?", new Object[]{path});db.close();}}4.实现文件下载阶段4.1建立SmartFileDownloader类用来实现文件的下载功能代码如下package com.smart.impl;import java.io.File;import java.io.RandomAccessFile;import .HttpURLConnection;import .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 android.content.Context;import android.util.Log;import com.smart.db.FileService;public class SmartFileDownloader {private static final String TAG = "SmartFileDownloader";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 SmartDownloadThread[] 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 void update(int threadId, int pos) { this.data.put(threadId, pos);}/*** 保存记录文件*/protected synchronized void saveLogFile() { 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 SmartFileDownloader(Context context, String downloadUrl, File fileSaveDir, int threadNum) {try {this.context = context;this.downloadUrl = downloadUrl;fileService = newFileService(this.context);URL url = new URL(this.downloadUrl);if(!fileSaveDir.exists())fileSaveDir.mkdirs();this.threads = newSmartDownloadThread[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 CLR2.0.50727; .NET CLR3.0.04506.30; .NET CLR3.0.4506.2152; .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);this.saveFile = new File(fileSaveDir, filename);/* 保存文件 */Map<Integer, Integer> logdata = fileService.getData(downloadUrl);if(logdata.size()>0){for(Map.Entry<Integer, Integer> entry : logdata.entrySet())data.put(entry.getKey(),entry.getValue());}this.block = (this.fileSize %this.threads.length)==0? this.fileSize /this.threads.length : this.fileSize /this.threads.length + 1;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);}}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(stI ndexOf('/') + 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.getHeader FieldKey(i).toLowerCase())){Matcher m =pile(".*filename=(.*)").matcher(mine.t oLowerCase());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 intdownload(SmartDownloadProgressListener 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();//清除数据for (int i = 0; i < this.threads.length; i++) {this.data.put(i+1, 0);}}for(int i = 0; i < this.threads.length; i++) {int downLength = this.data.get(i+1);if(downLength < this.block &&this.downloadSize<this.fileSize){ //该线程未完成下载时,继续下载this.threads[i] = new SmartDownloadThread(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) {// 循环判断是否下载完毕Thread.sleep(900);notFinish = false;//假定下载完成for (int i = 0; i < this.threads.length; i++){if (this.threads[i] != null&& !this.threads[i].isFinish()) {notFinish = true;//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 SmartDownloadThread(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);}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 voidprintResponseHeader(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());}}//打印日志private static void print(String msg){ Log.i(TAG, msg);}}4.2下载过程中的线程实现建立SmartDownloadThread类具体代码如下：package com.smart.impl;import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import .HttpURLConnection;import .URL;import android.util.Log;public class SmartDownloadThread extends Thread { private static final String TAG = "SmartDownloadThread";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 SmartFileDownloader downloader;public SmartDownloadThread(SmartFileDownloader 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 CLR2.0.50727; .NET CLR3.0.04506.30; .NET CLR3.0.4506.2152; .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.saveLogFile();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;}}4.3 建立interface SmartDownloadProgressListener 侦听线程的下载进度代码如下：package com.smart.impl;public interface SmartDownloadProgressListener { public void onDownloadSize(int size);}5.建立activity 实现下载的触发，和界面的实时更新具体代码如下：package com.smart.activoty.download;import java.io.File;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;importcom.smart.impl.SmartDownloadProgressListener; import com.smart.impl.SmartFileDownloader;public class SmartDownloadActivity extends Activity {private ProgressBar downloadbar;private EditText pathText;private TextView resultView;private Handler handler = new Handler(){@Override//信息public void handleMessage(Message msg) { switch (msg.what) {case 1:int size = msg.getData().getInt("size");downloadbar.setProgress(size);float result =(float)downloadbar.getProgress()/(float)downloadbar.getMax();int p = (int)(result*100);resultView.setText(p+"%");if(downloadbar.getProgress()==downloadbar.getM ax())Toast.makeText(SmartDownloadActivity.this, R.string.success, 1).show();break;case -1:Toast.makeText(SmartDownloadActivity.this, R.string.error, 1).show();break;}}};@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(yout.main);Button button =(Button)this.findViewById(R.id.button);downloadbar =(ProgressBar)this.findViewById(R.id.downloadbar); pathText =(EditText)this.findViewById(R.id.path);resultView =(TextView)this.findViewById(R.id.result);button.setOnClickListener(newView.OnClickListener() {@Overridepublic void onClick(View v) {String path =pathText.getText().toString();if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){File dir =Environment.getExternalStorageDirectory();//文件保存目录download(path, dir);}else{Toast.makeText(SmartDownloadActivity.this,R.string.sdcarderror, 1).show();}}});}//对于UI控件的更新只能由主线程(UI线程)负责，如果在非UI 线程更新UI控件，更新的结果不会反映在屏幕上，某些控件还会出错private void download(final String path, final File dir){new Thread(new Runnable() {@Overridepublic void run() {try {SmartFileDownloader loader = new SmartFileDownloader(SmartDownloadActivity.this, path, dir, 3);int length = loader.getFileSize();//获取文件的长度downloadbar.setMax(length);loader.download(new SmartDownloadProgressListener(){@Overridepublic void onDownloadSize(int size) {//可以实时得到文件下载的长度Message msg = new Message();msg.what = 1;msg.getData().putInt("size", size);handler.sendMessage(msg);}});} catch (Exception e) {Message msg = new Message();//信息提示msg.what = -1;msg.getData().putString("error", "下载失败");//如果下载错误，显示提示失败！handler.sendMessage(msg);}}}).start();//开始}}6.到此为止运行会报错，因为没有向sdcard的协数据的权限，访问Internet的权限这需要在AndroidManifest.xml配置具体代码如下：<?xml version="1.0"encoding="utf-8"?><manifestxmlns:android="/apk/res /android"package="com.smart.activoty.download"android:versionCode="1"android:versionName="1.0"><application android:icon="@drawable/icon" android:label="@string/app_name"><activityandroid:name=".SmartDownloadActivity"android:label="@string/app_name"> <intent-filter><actionandroid:name="android.intent.action.MAIN"/><categoryandroid:name="UNCHER"/> </intent-filter></activity></application><uses-sdk android:minSdkVersion="8"/><!-- 访问internet权限 --><uses-permissionandroid:name="android.permission.INTERNET"/><!-- 在SDCard中创建与删除文件权限 --><uses-permissionandroid:name="android.permission.MOUNT_UNMOUNT_FI LESYSTEMS"/><!-- 往SDCard写入数据权限 --><uses-permissionandroid:name="android.permission.WRITE_EXTERNAL_S TORAGE"/></manifest>。