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。
http://blog.csdn.net/shimiso/article/details/6763664 android 多线程断点续传下载 一
http://blog.csdn.net/shimiso/article/details/6763986 android 多线程断点续传下载 二
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/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:
[java] view
plaincopy
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)");
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
package cn.demo.dao;
import java.util.arraylist;
import java.util.list;
import android.content.context;
import android.database.cursor;
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) {
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);
* 得到下载具体信息
public synchronized list<downloadinfo> getinfos(string urlstr) {
list<downloadinfo> list = new arraylist<downloadinfo>();
string sql = "select thread_id, start_pos, end_pos,compelete_size,url from download_info where url=?";
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);
return list;
* 更新数据库中的下载信息
public synchronized void updatainfos(int threadid, int compeletesize, string urlstr) {
string sql = "update download_info set compelete_size=? where thread_id=? and url=?";
object[] bindargs = { compeletesize, threadid, urlstr };
database.execsql(sql, bindargs);
* 下载完成后删除数据库中的数据
public synchronized void delete(string url) {
database.delete("download_info", "url=?", new string[] { url });
}
package cn.demo.download;
import java.util.map;
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) {
minflater = layoutinflater.from(context);
this.data=data;
public void refresh(list<map<string, string>> data) {
this.notifydatasetchanged();
public void setonclick(onclicklistener click) {
this.click=click;
@override
public int getcount() {
return data.size();
public object getitem(int position) {
return data.get(position);
public long getitemid(int position) {
return position;
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
import java.util.arraylist;
import java.util.hashmap;
import android.app.listactivity;
import android.os.asynctask;
import android.os.bundle;
import android.os.handler;
import android.os.message;
import android.widget.linearlayout;
import android.widget.linearlayout.layoutparams;
import android.widget.progressbar;
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);
}
}
}
}
};
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");
map.put("name", "haozip_v2.8_x64_tiny.exe");
map.put("name", "haozip_v2.8_tiny.exe");
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);
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();
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) {
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) {
public int getstartpos() {
return startpos;
public void setstartpos(int startpos) {
public int getendpos() {
return endpos;
public void setendpos(int endpos) {
public int getcompeletesize() {
return compeletesize;
public void setcompeletesize(int compeletesize) {
public string tostring() {
return "downloadinfo [threadid=" + threadid
+ ", startpos=" + startpos + ", endpos=" + endpos
+ ", compeletesize=" + compeletesize +"]";
*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) {
public int getcomplete() {
return complete;
public void setcomplete(int complete) {
public string geturlstring() {
return urlstring;
public void seturlstring(string urlstring) {
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 android.util.log;
import cn.demo.dao.dao;
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;
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
[html] view
<?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_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:text="下载"
android:id="@+id/btn_start"
android:onclick="startdownload"/>
android:text="暂停"
android:visibility="gone"
android:id="@+id/btn_pause"
android:onclick="pausedownload"/>
</linearlayout>
</linearlayout>
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>
<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
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