android 之断点续传详解三部曲之[三] → 多任务同时下载

今天跟大家一起分享下android开发中比较难的一个环节,可能很多人看到这个标题就会感觉头很大,的确如果没有良好的编码能力和逻辑思维,这块是很难搞明白的,前面2次总结中已经为大家分享过有关技术的一些基本要领,我们先一起简单回顾下它的基本原理。

三部曲之一：http://blog.csdn.net/gulaer/article/details/8513825

三部曲之二：http://blog.csdn.net/gulaer/article/details/8513916

什么是多线程下载？

多线程下载其实就是迅雷,BT一些下载原理,通过多个线程同时和服务器连接,那么你就可以榨取到较高的带宽了,大致做法是将文件切割成N块,每块交给单独一个线程去下载,各自下载完成后将文件块组合成一个文件,程序上要完成做切割和组装的小算法

什么是断点续传?

断点续传,就是当我们下载未结束时候,退出保存下载进度,当下次打开继续下载的时接着上次的进度继续下载,不用每次下载都重新开始,那么有关断点续传的原理和实现手段,可参考我以前的一篇总结 http://blog.csdn.net/gulaer/article/details/8514146 里面详细讲解http协议断点续传的原理,务必要看懂,否则你无法真正理解本节代码

怎么完成多线程断点续传?

将两者合二为一需要程序记住每个文件块的下载进度,并保存入库,当下载程序启动时候你需要判断程序是否已经下载过该文件,并取出各个文件块的保存记录,换算出下载进度继续下载,在这里你需要掌握java多线程的基本知识,handler的使用,以及集合,算法,文件操作等基本技能,同时还要解决sqlite数据库的同步问题,因为它是不太怎么支持多线程操作的,控制不好经常会出现库被锁定的异常,同时在android2.3以后就不能activity中直接操作http,否则你将收到系统送上的NetworkOnMainThreadException异常,在UI体验上一定记住要使用异步完成,既然大致思路已经清楚,下面我们开始分析程序:

DBHelper.java

package cn.demo.DBHelper;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;/** * 建立一个数据库帮助类 */public class DBHelper extends SQLiteOpenHelper {// download.db-->数据库名public DBHelper(Context context) {super(context, "download.db", null, 1);}/** * 在download.db数据库下创建一个download_info表存储下载信息 */@Overridepublic void onCreate(SQLiteDatabase db) {db.execSQL("create table download_info(_id integer PRIMARY KEY AUTOINCREMENT, thread_id integer, "+ "start_pos integer, end_pos integer, compelete_size integer,url char)");}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}}

数据库操作要借助单例和同步,来保证线程的执行顺序,以免多个线程争相抢用sqlite资源导致异常出现

Dao.java

package cn.demo.Dao;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import cn.demo.DBHelper.DBHelper;import cn.demo.entity.DownloadInfo;/** * 一个业务类 */public class Dao {private static Dao dao = null;private Context context;private Dao(Context context) {this.context = context;}public static Dao getInstance(Context context) {if (dao == null) {dao = new Dao(context);}return dao;}public SQLiteDatabase getConnection() {SQLiteDatabase sqliteDatabase = null;try {sqliteDatabase = new DBHelper(context).getReadableDatabase();} catch (Exception e) {}return sqliteDatabase;}/** * 查看数据库中是否有数据 */public synchronized boolean isHasInfors(String urlstr) {SQLiteDatabase database = getConnection();int count = -1;Cursor cursor = null;try {String sql = "select count(*)  from download_info where url=?";cursor = database.rawQuery(sql, new String[] { urlstr });if (cursor.moveToFirst()) {count = cursor.getInt(0);}} catch (Exception e) {e.printStackTrace();} finally {if (null != database) {database.close();}if (null != cursor) {cursor.close();}}return count == 0;}/** * 保存 下载的具体信息 */public synchronized void saveInfos(List<DownloadInfo> infos) {SQLiteDatabase database = getConnection();try {for (DownloadInfo info : infos) {String sql = "insert into download_info(thread_id,start_pos, end_pos,compelete_size,url) values (?,?,?,?,?)";Object[] bindArgs = { info.getThreadId(), info.getStartPos(), info.getEndPos(), info.getCompeleteSize(), info.getUrl() };database.execSQL(sql, bindArgs);}} catch (Exception e) {e.printStackTrace();} finally {if (null != database) {database.close();}}}/** * 得到下载具体信息 */public synchronized List<DownloadInfo> getInfos(String urlstr) {List<DownloadInfo> list = new ArrayList<DownloadInfo>();SQLiteDatabase database = getConnection();Cursor cursor = null;try {String sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";cursor = database.rawQuery(sql, new String[] { urlstr });while (cursor.moveToNext()) {DownloadInfo info = new DownloadInfo(cursor.getInt(0), cursor.getInt(1), cursor.getInt(2), cursor.getInt(3),cursor.getString(4));list.add(info);}} catch (Exception e) {e.printStackTrace();} finally {if (null != database) {database.close();}if (null != cursor) {cursor.close();}}return list;}/** * 更新数据库中的下载信息 */public synchronized void updataInfos(int threadId, int compeleteSize, String urlstr) {SQLiteDatabase database = getConnection();try {String sql = "update download_info set compelete_size=? where thread_id=? and url=?";Object[] bindArgs = { compeleteSize, threadId, urlstr };database.execSQL(sql, bindArgs);} catch (Exception e) {e.printStackTrace();} finally {if (null != database) {database.close();}}}/** * 下载完成后删除数据库中的数据 */public synchronized void delete(String url) {SQLiteDatabase database = getConnection();try {database.delete("download_info", "url=?", new String[] { url });} catch (Exception e) {e.printStackTrace();} finally {if (null != database) {database.close();}}}}

DownLoadAdapter.java

package cn.demo.download;import java.util.List;import java.util.Map;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.View.OnClickListener;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.TextView;public class DownLoadAdapter extends BaseAdapter {private LayoutInflater mInflater;private List<Map<String, String>> data;private Context context;private OnClickListener click;public DownLoadAdapter(Context context, List<Map<String, String>> data) {this.context = context;mInflater = LayoutInflater.from(context);this.data = data;}public void refresh(List<Map<String, String>> data) {this.data = data;this.notifyDataSetChanged();}public void setOnclick(OnClickListener click) {this.click = click;}@Overridepublic int getCount() {return data.size();}@Overridepublic Object getItem(int position) {return data.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(final int position, View convertView, ViewGroup parent) {final Map<String, String> bean = data.get(position);ViewHolder holder = null;if (convertView == null) {convertView = mInflater.inflate(R.layout.list_item, null);holder = new ViewHolder();holder.resouceName = (TextView) convertView.findViewById(R.id.tv_resouce_name);holder.startDownload = (Button) convertView.findViewById(R.id.btn_start);holder.pauseDownload = (Button) convertView.findViewById(R.id.btn_pause);convertView.setTag(holder);} else {holder = (ViewHolder) convertView.getTag();}holder.resouceName.setText(bean.get("name"));return convertView;}public OnClickListener getClick() {return click;}public void setClick(OnClickListener click) {this.click = click;}private class ViewHolder {public TextView resouceName;public Button startDownload;public Button pauseDownload;}}

注意子线程不要影响主UI线程,灵活运用task和handler,各取所长,保证用户体验,handler通常在主线程中有利于专门负责处理UI的一些工作

MainActivity.java

package cn.demo.download;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import android.app.ListActivity;import android.os.AsyncTask;import android.os.Bundle;import android.os.Handler;import android.os.Message;import android.view.View;import android.widget.Button;import android.widget.LinearLayout;import android.widget.LinearLayout.LayoutParams;import android.widget.ProgressBar;import android.widget.TextView;import android.widget.Toast;import cn.demo.entity.LoadInfo;import cn.demo.service.Downloader;public class MainActivity extends ListActivity {// 固定下载的资源路径，这里可以设置网络上的地址private static final String URL = "http://download.haozip.com/";// 固定存放下载的音乐的路径：SD卡目录下private static final String SD_PATH = "/mnt/sdcard/";// 存放各个下载器private Map<String, Downloader> downloaders = new HashMap<String, Downloader>();// 存放与下载器对应的进度条private Map<String, ProgressBar> ProgressBars = new HashMap<String, ProgressBar>();/** * 利用消息处理机制适时更新进度条 */private Handler mHandler = new Handler() {public void handleMessage(Message msg) {if (msg.what == 1) {String url = (String) msg.obj;int length = msg.arg1;ProgressBar bar = ProgressBars.get(url);if (bar != null) {// 设置进度条按读取的length长度更新bar.incrementProgressBy(length);if (bar.getProgress() == bar.getMax()) {LinearLayout layout = (LinearLayout) bar.getParent();TextView resouceName = (TextView) layout.findViewById(R.id.tv_resouce_name);Toast.makeText(MainActivity.this, "[" + resouceName.getText() + "]下载完成！", Toast.LENGTH_SHORT).show();// 下载完成后清除进度条并将map中的数据清空layout.removeView(bar);ProgressBars.remove(url);downloaders.get(url).delete(url);downloaders.get(url).reset();downloaders.remove(url);Button btn_start = (Button) layout.findViewById(R.id.btn_start);Button btn_pause = (Button) layout.findViewById(R.id.btn_pause);btn_pause.setVisibility(View.GONE);btn_start.setVisibility(View.GONE);}}}}};@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);showListView();}// 显示listView，这里可以随便添加private void showListView() {List<Map<String, String>> data = new ArrayList<Map<String, String>>();Map<String, String> map = new HashMap<String, String>();map.put("name", "haozip_v3.1.exe");data.add(map);map = new HashMap<String, String>();map.put("name", "haozip_v3.1_hj.exe");data.add(map);map = new HashMap<String, String>();map.put("name", "haozip_v2.8_x64_tiny.exe");data.add(map);map = new HashMap<String, String>();map.put("name", "haozip_v2.8_tiny.exe");data.add(map);DownLoadAdapter adapter = new DownLoadAdapter(this, data);setListAdapter(adapter);}/** * 响应开始下载按钮的点击事件 */public void startDownload(View v) {// 得到textView的内容LinearLayout layout = (LinearLayout) v.getParent();String resouceName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();String urlstr = URL + resouceName;String localfile = SD_PATH + resouceName;// 设置下载线程数为4，这里是我为了方便随便固定的String threadcount = "4";DownloadTask downloadTask = new DownloadTask(v);downloadTask.execute(urlstr, localfile, threadcount);};class DownloadTask extends AsyncTask<String, Integer, LoadInfo> {Downloader downloader = null;View v = null;String urlstr = null;public DownloadTask(final View v) {this.v = v;}@Overrideprotected void onPreExecute() {Button btn_start = (Button) ((View) v.getParent()).findViewById(R.id.btn_start);Button btn_pause = (Button) ((View) v.getParent()).findViewById(R.id.btn_pause);btn_start.setVisibility(View.GONE);btn_pause.setVisibility(View.VISIBLE);}@Overrideprotected LoadInfo doInBackground(String... params) {urlstr = params[0];String localfile = params[1];int threadcount = Integer.parseInt(params[2]);// 初始化一个downloader下载器downloader = downloaders.get(urlstr);if (downloader == null) {downloader = new Downloader(urlstr, localfile, threadcount, MainActivity.this, mHandler);downloaders.put(urlstr, downloader);}if (downloader.isdownloading())return null;// 得到下载信息类的个数组成集合return downloader.getDownloaderInfors();}@Overrideprotected void onPostExecute(LoadInfo loadInfo) {if (loadInfo != null) {// 显示进度条showProgress(loadInfo, urlstr, v);// 调用方法开始下载downloader.download();}}};/** * 显示进度条 */private void showProgress(LoadInfo loadInfo, String url, View v) {ProgressBar bar = ProgressBars.get(url);if (bar == null) {bar = new ProgressBar(this, null, android.R.attr.progressBarStyleHorizontal);bar.setMax(loadInfo.getFileSize());bar.setProgress(loadInfo.getComplete());ProgressBars.put(url, bar);LinearLayout.LayoutParams params = new LayoutParams(LayoutParams.FILL_PARENT, 5);((LinearLayout) ((LinearLayout) v.getParent()).getParent()).addView(bar, params);}}/** * 响应暂停下载按钮的点击事件 */public void pauseDownload(View v) {LinearLayout layout = (LinearLayout) v.getParent();String resouceName = ((TextView) layout.findViewById(R.id.tv_resouce_name)).getText().toString();String urlstr = URL + resouceName;downloaders.get(urlstr).pause();Button btn_start = (Button) ((View) v.getParent()).findViewById(R.id.btn_start);Button btn_pause = (Button) ((View) v.getParent()).findViewById(R.id.btn_pause);btn_pause.setVisibility(View.GONE);btn_start.setVisibility(View.VISIBLE);}}

这是一个信息的实体,记录了一些字典信息,可以认为是一个简单bean对象

DownloadInfo.java

package cn.demo.entity;/** * 创建一个下载信息的实体类 */public class DownloadInfo {private int threadId;// 下载器idprivate int startPos;// 开始点private int endPos;// 结束点private int compeleteSize;// 完成度private String url;// 下载器网络标识public DownloadInfo(int threadId, int startPos, int endPos, int compeleteSize, String url) {this.threadId = threadId;this.startPos = startPos;this.endPos = endPos;this.compeleteSize = compeleteSize;this.url = url;}public DownloadInfo() {}public String getUrl() {return url;}public void setUrl(String url) {this.url = url;}public int getThreadId() {return threadId;}public void setThreadId(int threadId) {this.threadId = threadId;}public int getStartPos() {return startPos;}public void setStartPos(int startPos) {this.startPos = startPos;}public int getEndPos() {return endPos;}public void setEndPos(int endPos) {this.endPos = endPos;}public int getCompeleteSize() {return compeleteSize;}public void setCompeleteSize(int compeleteSize) {this.compeleteSize = compeleteSize;}@Overridepublic String toString() {return "DownloadInfo [threadId=" + threadId + ", startPos=" + startPos + ", endPos=" + endPos + ", compeleteSize=" + compeleteSize+ "]";}}

LoadInfo.java

package cn.demo.entity;/** * 自定义的一个记载下载器详细信息的类 */public class LoadInfo {public int fileSize;// 文件大小private int complete;// 完成度private String urlstring;// 下载器标识public LoadInfo(int fileSize, int complete, String urlstring) {this.fileSize = fileSize;this.complete = complete;this.urlstring = urlstring;}public LoadInfo() {}public int getFileSize() {return fileSize;}public void setFileSize(int fileSize) {this.fileSize = fileSize;}public int getComplete() {return complete;}public void setComplete(int complete) {this.complete = complete;}public String getUrlstring() {return urlstring;}public void setUrlstring(String urlstring) {this.urlstring = urlstring;}@Overridepublic String toString() {return "LoadInfo [fileSize=" + fileSize + ", complete=" + complete + ", urlstring=" + urlstring + "]";}}

这是一个核心类,专门用来处理下载的

Downloader.java

package cn.demo.service;import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;import java.util.ArrayList;import java.util.List;import android.content.Context;import android.os.Handler;import android.os.Message;import android.util.Log;import cn.demo.Dao.Dao;import cn.demo.entity.DownloadInfo;import cn.demo.entity.LoadInfo;public class Downloader {private String urlstr;// 下载的地址private String localfile;// 保存路径private int threadcount;// 线程数private Handler mHandler;// 消息处理器private int fileSize;// 所要下载的文件的大小private Context context;private List<DownloadInfo> infos;// 存放下载信息类的集合private static final int INIT = 1;// 定义三种下载的状态：初始化状态，正在下载状态，暂停状态private static final int DOWNLOADING = 2;private static final int PAUSE = 3;private int state = INIT;public Downloader(String urlstr, String localfile, int threadcount, Context context, Handler mHandler) {this.urlstr = urlstr;this.localfile = localfile;this.threadcount = threadcount;this.mHandler = mHandler;this.context = context;}/** * 判断是否正在下载 */public boolean isdownloading() {return state == DOWNLOADING;}/** * 得到downloader里的信息 首先进行判断是否是第一次下载，如果是第一次就要进行初始化，并将下载器的信息保存到数据库中 如果不是第一次下载，那就要从数据库中读出之前下载的信息（起始位置，结束为止，文件大小等），并将下载信息返回给下载器 */public LoadInfo getDownloaderInfors() {if (isFirst(urlstr)) {Log.v("TAG", "isFirst");init();int range = fileSize / threadcount;infos = new ArrayList<DownloadInfo>();for (int i = 0; i < threadcount - 1; i++) {DownloadInfo info = new DownloadInfo(i, i * range, (i + 1) * range - 1, 0, urlstr);infos.add(info);}DownloadInfo info = new DownloadInfo(threadcount - 1, (threadcount - 1) * range, fileSize - 1, 0, urlstr);infos.add(info);// 保存infos中的数据到数据库Dao.getInstance(context).saveInfos(infos);// 创建一个LoadInfo对象记载下载器的具体信息LoadInfo loadInfo = new LoadInfo(fileSize, 0, urlstr);return loadInfo;} else {// 得到数据库中已有的urlstr的下载器的具体信息infos = Dao.getInstance(context).getInfos(urlstr);Log.v("TAG", "not isFirst size=" + infos.size());int size = 0;int compeleteSize = 0;for (DownloadInfo info : infos) {compeleteSize += info.getCompeleteSize();size += info.getEndPos() - info.getStartPos() + 1;}return new LoadInfo(size, compeleteSize, urlstr);}}/** * 初始化 */private void init() {try {URL url = new URL(urlstr);HttpURLConnection connection = (HttpURLConnection) url.openConnection();connection.setConnectTimeout(5000);connection.setRequestMethod("GET");fileSize = connection.getContentLength();File file = new File(localfile);if (!file.exists()) {file.createNewFile();}// 本地访问文件RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");accessFile.setLength(fileSize);accessFile.close();connection.disconnect();} catch (Exception e) {e.printStackTrace();}}/** * 判断是否是第一次 下载 */private boolean isFirst(String urlstr) {return Dao.getInstance(context).isHasInfors(urlstr);}/** * 利用线程开始下载数据 */public void download() {if (infos != null) {if (state == DOWNLOADING)return;state = DOWNLOADING;for (DownloadInfo info : infos) {new MyThread(info.getThreadId(), info.getStartPos(), info.getEndPos(), info.getCompeleteSize(), info.getUrl()).start();}}}public class MyThread extends Thread {private int threadId;private int startPos;private int endPos;private int compeleteSize;private String urlstr;public MyThread(int threadId, int startPos, int endPos, int compeleteSize, String urlstr) {this.threadId = threadId;this.startPos = startPos;this.endPos = endPos;this.compeleteSize = compeleteSize;this.urlstr = urlstr;}@Overridepublic void run() {HttpURLConnection connection = null;RandomAccessFile randomAccessFile = null;InputStream is = null;try {URL url = new URL(urlstr);connection = (HttpURLConnection) url.openConnection();connection.setConnectTimeout(5000);connection.setRequestMethod("GET");// 设置范围，格式为Range：bytes x-y;connection.setRequestProperty("Range", "bytes=" + (startPos + compeleteSize) + "-" + endPos);randomAccessFile = new RandomAccessFile(localfile, "rwd");randomAccessFile.seek(startPos + compeleteSize);// 将要下载的文件写到保存在保存路径下的文件中is = connection.getInputStream();byte[] buffer = new byte[4096];int length = -1;while ((length = is.read(buffer)) != -1) {randomAccessFile.write(buffer, 0, length);compeleteSize += length;// 更新数据库中的下载信息Dao.getInstance(context).updataInfos(threadId, compeleteSize, urlstr);// 用消息将下载信息传给进度条，对进度条进行更新Message message = Message.obtain();message.what = 1;message.obj = urlstr;message.arg1 = length;mHandler.sendMessage(message);if (state == PAUSE) {return;}}} catch (Exception e) {e.printStackTrace();}}}// 删除数据库中urlstr对应的下载器信息public void delete(String urlstr) {Dao.getInstance(context).delete(urlstr);}// 设置暂停public void pause() {state = PAUSE;}// 重置下载状态public void reset() {state = INIT;}}

下面就是布局文件了：

main.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/llRoot"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical" >    <ListView        android:id="@android:id/list"        android:layout_width="fill_parent"        android:layout_height="fill_parent" >    </ListView></LinearLayout>

list_item.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="wrap_content"    android:orientation="vertical" >    <LinearLayout        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:layout_marginBottom="5dip"        android:orientation="horizontal" >        <TextView            android:id="@+id/tv_resouce_name"            android:layout_width="fill_parent"            android:layout_height="wrap_content"            android:layout_weight="1" />        <Button            android:id="@+id/btn_start"            android:layout_width="fill_parent"            android:layout_height="wrap_content"            android:layout_weight="1"            android:onClick="startDownload"            android:text="下载" />        <Button            android:id="@+id/btn_pause"            android:layout_width="fill_parent"            android:layout_height="wrap_content"            android:layout_weight="1"            android:onClick="pauseDownload"            android:text="暂停"            android:visibility="gone" />    </LinearLayout></LinearLayout>

最后是配置文件：

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="cn.demo.download"    android:versionCode="1"    android:versionName="1.0">    <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="8" /><uses-permission android:name="android.permission.INTERNET"/>　<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>    <application android:label="@string/app_name"        android:icon="@drawable/ic_launcher"        android:theme="@style/AppTheme"><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></manifest>

效果图：

源码下载地址：http://download.csdn.net/detail/gulaer/5005135

原文地址：http://blog.csdn.net/shimiso/article/details/6763986 非常感谢原作者.