网络多线程断点下载

我们编写的是Andorid的HTTP多线程断点下载应用程序。因为之间我们学习的学习积累，直接使用单线程下载HTTP文件对我们来说是一件非常简单的事。那么，多线程断点下载的难点在哪里？1.多线程下载，2.支持断点。

多线程下载：



如何才能从文件的指定位置处开始下载文件？（比如从50MB开始）这一点我们可以通过HTTP请求信息头来设置，还记得HTTP请求信息头的“Range”属性吗？

断点：

首要问题（多线程下载）已经被我们解决了，支持断点下载想必大家也已经想到了。就是将下载的进度保存到文件中，但在Android中却不能这么做。通过老黎的试验，在Android平台中，我们需要向文件中写出下载的文件数据，还需要向另一个文件中写出下载进度，这样会出错。这样会导致有一个文件的内容没有被写出。所以我们就不能以文件的方式来保存下载进度，但可以通过数据库的方式保存下载进度。

这两大问题我们已经有了解决思路，那么就开始动手编写吧！

1.创建Android工程

Project name:MulThreadDownloader

BuildTarget:Android2.1

Application name：多线程断点下载

Package name:com.changcheng.download

Create Activity:MulThreadDownloader

Min SDK Version:7

2.AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.changcheng.download" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".MulThreadDownloader" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion="7" /> <!-- 在SDCard中创建与删除文件权限 --> <uses-permissionandroid:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/> <!-- 往SDCard写入数据权限 --> <uses-permissionandroid:name="android.permission.WRITE_EXTERNAL_STORAGE"/> <!-- 访问internet权限 --> <uses-permission android:name="android.permission.INTERNET"/> </manifest>

3.strings.xml

<?xml version="1.0" encoding="utf-8"?> <resources> <string name="hello">Hello World, DownloadActivity!</string> <string name="app_name">多线程断点下载</string> <string name="path">下载路径</string> <string name="downloadbutton">下载</string> <string name="sdcarderror">SDCard不存在或者写保护</string> </resources>

4.main.xml

<?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" > <!-- 下载路径 --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/path" /> <EditText android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="http://www.winrar.com.cn/download/wrar380sc.exe" android:id="@+id/path" /> <!-- 下载按钮 --> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/downloadbutton" android:id="@+id/button" /> <!-- 进度条 --> <ProgressBar android:layout_width="fill_parent" android:layout_height="20dip" style="?android:attr/progressBarStyleHorizontal" android:id="@+id/downloadbar"/> <!-- 进度% --> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center" android:id="@+id/resultView" /> </LinearLayout>

5.MulThreadDownloader

package com.changcheng.download; import java.io.File; import com.changcheng.net.download.DownloadProgressListener; import com.changcheng.net.download.FileDownloader; import com.changcheng.download.R; 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 MulThreadDownloader extends Activity { private EditText pathText; private ProgressBar progressBar; private TextView resultView; private Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { if(!Thread.currentThread().isInterrupted()){ switch (msg.what) { case 1: // 获取当前文件下载的进度 int size = msg.getData().getInt("size"); progressBar.setProgress(size); int result = (int)(((float)size/(float)progressBar.getMax()) * 100); resultView.setText(result+ "%"); if(progressBar.getMax() == size){ Toast.makeText(MulThreadDownloader.this, "文件下载完成", 1).show(); } break; case -1: String error = msg.getData().getString("error"); Toast.makeText(MulThreadDownloader.this, error, 1).show(); break; } } super.handleMessage(msg); } }; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); pathText = (EditText)this.findViewById(R.id.path); progressBar = (ProgressBar)this.findViewById(R.id.downloadbar); resultView = (TextView)this.findViewById(R.id.resultView); Button button = (Button)this.findViewById(R.id.button); button.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { String path = pathText.getText().toString(); if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){ //下载文件需要很长的时间，主线程是不能够长时间被阻塞，如果主线程被长时间阻塞， 那么Android被回收应用 download(path, Environment.getExternalStorageDirectory()); }else{ Toast.makeText(MulThreadDownloader.this, R.string.sdcarderror, 1).show(); } } }); } /** * 下载文件 * @param path 下载路径 * @param saveDir 文件保存目录 */ //对于Android的UI控件，只能由主线程负责显示界面的更新，其他线程不能直接更新UI控件的显示 public void download(final String path, final File saveDir){ new Thread(new Runnable() { @Override public void run() { FileDownloader downer = newFileDownloader(MulThreadDownloader.this, path, saveDir, 3); progressBar.setMax(downer.getFileSize());//设置进度条的最大刻度 try { downer.download(new DownloadProgressListener(){ @Override public void onDownloadSize(int size) { Message msg = new Message(); msg.what = 1; msg.getData().putInt("size", size); handler.sendMessage(msg);//发送消息 }}); } catch (Exception e) { Message msg = new Message(); msg.what = -1; msg.getData().putString("error", "下载失败"); handler.sendMessage(msg); } } }).start(); } }

6.FileDownload

package com.changcheng.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 com.changcheng.download.service.FileService; import android.content.Context; import android.util.Log; /** * 文件下载器 * @author lihuoming@sohu.com * */ public class FileDownloader { private Context context; private FileService fileService; private static final String TAG = "FileDownloader"; /* 已下载文件大小 */ private int downloadSize = 0; /* 原始文件大小 */ private int fileSize = 0; /* 线程数 */ private DownloadThread[] threads; /* 下载路径 */ private URL url; /* 本地保存文件 */ private File saveFile; /* 下载记录文件 */ private File logFile; /* 缓存各线程最后下载的位置*/ private Map<Integer, Integer> data = new ConcurrentHashMap<Integer, Integer>(); /* 每条线程下载的大小 */ private int block; private String downloadUrl;//下载路径 /** * 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 FileDownloader(Context context, String downloadUrl, File fileSaveDir, intthreadNum) { try { this.context = context; this.downloadUrl = downloadUrl; fileService = new FileService(context); this.url = new URL(downloadUrl); if(!fileSaveDir.exists()) fileSaveDir.mkdirs(); this.threads = newDownloadThread[threadNum]; HttpURLConnection conn = (HttpURLConnection)url.openConnection(); conn.setConnectTimeout(6*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("无法获知文件大小 "); 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){ data.putAll(logdata); } this.block = 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)-(this.block * i); } print("已经下载的长度"+ this.downloadSize); } }else{ throw new RuntimeException("服务器响应错误 "); } } catch (Exception e) { print(e.toString()); throw new RuntimeException("连接不到下载路径 "); } } /** * 获取文件名 */ private String getFileName(HttpURLConnection conn) { String filename =this.url.toString().substring(this.url.toString().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 { if(this.data.size() != this.threads.length){ this.data.clear(); for (int i = 0; i < this.threads.length; i++) { this.data.put(i+1, this.block * i); } } for (int i = 0; i < this.threads.length; i++) { int downLength = this.data.get(i+1) - (this.block * i); if(downLength < this.block && this.data.get(i+1)<this.fileSize){//该线程未完成下载时,继续下载 RandomAccessFile randOut = newRandomAccessFile(this.saveFile, "rw"); if(this.fileSize>0) randOut.setLength(this.fileSize); randOut.seek(this.data.get(i+1)); this.threads[i] = new DownloadThread(this, this.url, randOut, 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 RandomAccessFile randOut = newRandomAccessFile(this.saveFile, "rw"); randOut.seek(this.data.get(i+1)); this.threads[i] = new DownloadThread(this,this.url, randOut, 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("下载失败"); } 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); } }

7.DownloadProgressListener

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

8.FileService

package com.changcheng.download.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); } /** * 获取线程最后下载位置 * @param path * @return */ public Map<Integer, Integer> getData(String path){ SQLiteDatabase db = openHelper.getReadableDatabase(); Cursor cursor = db.rawQuery("select threadid, position from filedown 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; } /** * 保存下载线程初始位置 * @param path * @param map */ public void save(String path, Map<Integer, Integer> map){//int threadid, intposition SQLiteDatabase db = openHelper.getWritableDatabase(); db.beginTransaction(); try{ for(Map.Entry<Integer, Integer> entry : map.entrySet()){ db.execSQL("insert into filedown(downpath, threadid, position) values(?,?,?)", new Object[]{path, entry.getKey(), entry.getValue()}); } db.setTransactionSuccessful(); }finally{ db.endTransaction(); } db.close(); } /** * 实时更新线程的最后下载位置 * @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 filedown set position=? 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，清掉该文件对应的下载记录 * @param path */ public void delete(String path){ SQLiteDatabase db = openHelper.getWritableDatabase(); db.execSQL("delete from filedown where downpath=?", new Object[]{path}); db.close(); } }

9.DownloadThread

package com.changcheng.net.download; 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 RandomAccessFile saveFile; private URL downUrl; private int block; /* 下载开始位置 */ private int threadId = -1; private int startPos; private int downLength; private boolean finish = false; private FileDownloader downloader; public DownloadThread(FileDownloader downloader, URL downUrl, RandomAccessFile saveFile, int block, int startPos, int threadId) { this.downUrl = downUrl; this.saveFile = saveFile; this.block = block; this.startPos = startPos; this.downloader = downloader; this.threadId = threadId; this.downLength = startPos - (block * (threadId - 1)); } @Override public void run() { if(downLength < block){//未下载完成 try { HttpURLConnection http = (HttpURLConnection)downUrl.openConnection(); 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"); http.setRequestProperty("Range", "bytes=" + this.startPos + "-"); 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(); int max = block>1024 ? 1024 : (block>10 ? 10 : 1); byte[] buffer = new byte[max]; int offset = 0; print("线程 " + this.threadId + "从位置"+ this.startPos+ "开始下载 "); while (downLength < block && (offset = inStream.read(buffer, 0, max)) != -1) { saveFile.write(buffer, 0, offset); downLength += offset; downloader.update(this.threadId, block * (threadId - 1) + downLength); downloader.saveLogFile(); downloader.append(offset); int spare = block-downLength;//求剩下的字节数 if(spare < max) max = (int) spare; } saveFile.close(); inStream.close(); print("线程 " + this.threadId + "完成下载 "); this.finish = true; this.interrupt(); } catch (Exception e) { this.downLength = -1; print("线程"+ 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; } }

11.DBOpenHelper

package com.changcheng.download.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 = "download.db"; private static final int VERSION = 2; public DBOpenHelper(Context context) { super(context, DBNAME, null, VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL("CREATE TABLE IF NOT EXISTS filedown (id integer primary key autoincrement, downpath varchar(100), threadid INTEGER, position INTEGER)"); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { db.execSQL("DROP TABLE IF EXISTS filedown"); onCreate(db); } }

结束！