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。
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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：
<?xml version="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：
<?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">
<!-- 下载路径 -->
<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>
<!-- 下载按钮 -->
<button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/downloadbutton"
android:id="@+id/button"/>
<!-- 进度条 -->
<progressbar
android:layout_width="fill_parent"
android:layout_height="20dip"
style="?android:attr/progressbarstylehorizontal"
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:
<?xml version="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>
<!-- 在sdcard中创建与删除文件权限 -->
<uses-permission android:name="android.permission.mount_unmount_filesystems"/>
<!-- 往sdcard写入数据权限 -->
<uses-permission android:name="android.permission.write_external_storage"/>
<!-- 访问internet权限 -->
<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：
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