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?
原理和实现手段,可参考我以前的一篇总结http://blog.csdn.net/shimiso/article/details/5956314 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:
SQLiteOpenHelper类
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
*/
@Override
public 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)");
}
@Override
public 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
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
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;
}
@Override
public int getCount() {
return data.size();
}
@Override
public Object getItem(int position) {
return data.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public 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
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);
}
}
}
}
};
@Override
public 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;
}
@Override
protected 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);
}
@Override
protected 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();
}
@Override
protected 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
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id
private 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;
}
@Override
public String toString() {
return "DownloadInfo [threadId=" + threadId
+ ", startPos=" + startPos + ", endPos=" + endPos
+ ", compeleteSize=" + compeleteSize +"]";
}
}
LoadInfo
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;
}
@Override
public 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
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.AsyncTask;
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;
}
@Override
public 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;
}
}
以下是些xml文件
<?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="wrap_content">
<LinearLayout
android:orientation="horizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="5dip">
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:id="@+id/tv_resouce_name"/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="下载"
android:id="@+id/btn_start"
android:onClick="startDownload"/>
<Button
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="暂停"
android:visibility="gone"
android:id="@+id/btn_pause"
android:onClick="pauseDownload"/>
</LinearLayout>
</LinearLayout>
<?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"
android:id="@+id/llRoot">
<ListView android:id="@android:id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
</ListView>
</LinearLayout>
<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>
运行效果如下
源码下载地址
