本示例介绍在AndroID平台下通过http协议实现断点续传下载。
多线程断点需要的功能
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。
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
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,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(),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,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,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",*/*"); 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,1024)) != -1) { threadfile.write(buffer,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; }} 以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持编程小技巧。
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