我们编写的是Andorid的HTTP协议多线程断点下载应用程序。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，多线程断点需要什么功能？

1.多线程下载，

2.支持断点。

使用多线程的好处：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();//获取下载文件的长度 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

程序结构如下图所示：

string.xml文件中代码：

<"1.0" encoding="utf-8"?> <resources> <string name="hello">Hello World, MainActivity!</string> <string name="app_name">Android网络多线程断点下载</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> <string name="success">下载完成</string> <string name="error">下载失败</string> </resources>

main.xml文件中代码：

<"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/path"/> <EditText android:id="@+id/path" android:text="http://www.winrar.com.cn/download/wrar380sc.exe" android:layout_width="fill_parent" android:layout_height="wrap_content"> </EditText> <> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/downloadbutton" android:id="@+id/button"/> <> <ProgressBar android:layout_width="fill_parent" android:layout_height="20dip" android:id="@+id/downloadbar" /> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center" android:id="@+id/resultView" /> </LinearLayout>

AndroidManifest.xml文件中代码:

<"1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.android.downloader" android:versionCode="1" android:versionName="1.0"> <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".MainActivity" 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-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/> <> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> <> <uses-permission android:name="android.permission.INTERNET"/> </manifest>

MainActivity中代码：

package com.android.downloader; import java.io.File; import com.android.network.DownloadProgressListener; import com.android.network.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 MainActivity 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(){ @Override public 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(MainActivity.this, R.string.success, 1).show(); } break; case -1: Toast.makeText(MainActivity.this, R.string.error, 1).show(); break; } } }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); downloadpathText = (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) { // TODO Auto-generated method stub String path = downloadpathText.getText().toString(); System.out.println(Environment.getExternalStorageState()+"------"+Environment.MEDIA_MOUNTED); if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){ download(path, Environment.getExternalStorageDirectory()); }else{ Toast.makeText(MainActivity.this, R.string.sdcarderror, 1).show(); } } }); } /** * 主线程(UI线程) * 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 * @param path * @param savedir */ private void download(final String path, final File savedir) { new Thread(new Runnable() { @Override public void run() { FileDownloader loader = new FileDownloader(MainActivity.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() { @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(); msg.what = 1; msg.getData().putInt("size", size); handler.sendMessage(msg);//发送消息 } }); } catch (Exception e) { handler.obtainMessage(-1).sendToTarget(); } } }).start(); } }

DBOpenHelper中代码：

package com.android.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 = "down.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); } }

FileService中代码：

package com.android.service; import java.util.HashMap; import java.util.Map; import android.content.Context; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; 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(); } }

DownloadProgressListener中代码：

package com.android.network; public interface DownloadProgressListener { public void onDownloadSize(int size); }

FileDownloader中代码：

package com.android.network; 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.android.service.FileService; import android.content.Context; import android.util.Log; 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); } /** * 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 * @param conn * @return */ 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){ 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 } } 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; } } 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); } }

DownloadThread 中代码：

package com.android.network;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; } @Override public 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; }}

运行效果如下：