通过上面几节的介绍，对Java和Android中的线程应该有了一个简单的了解，下面通过上面讲解的一些知识实现一个简单的多线程下载。在这个下载功能的实现中，需要用到以下知识点：多线程、Android中的服务、访问网络资源、通知、文件的存储等。首先了解一下这个实例的界面，如图13.11至图13.14所示。

  这个实例界面很少，只要一个按钮就行了，下面来看看实现过程。

  (1)单击下载的事件处理。单击下载按钮会跳转到一个服务，把要下载的文件地址传过去。

Eutton button = (Button) findViewByld(R.id.do讨nload); :.

button.setOnClickListener(new OnClickLis七巳门8工(){

^Override 1 飞

public void onClick (View v) {

String path = "http://www.etwap.cn/cms/aFetion/

etfeti cmV2.4.apk";

Intent intent = new Intent () ; ■■-

intent.putExtra("p$th”， path);

intent.setclass(TestDownload_lActivity.this,

DownloadService.class)；

startservice(intent);

}

})；

  (2)下载的服务类，主要的下载都在这个类中实现。

  继承Service类，覆盖方法，在onStartCommand方法中获取界面传过来的值，判断SD卡的情况，获取NotificationManager的实例，设置通知栏的一些属性，代码如下：

@Override

public int onStartCommand(Intent intent, int flags, int startld) {

path = intent.getStringExtra("path");

//创建文件

if(android.os.Environment.MEDIA^MOUNTED.equals(android.os.

Environment.getExternaLStorageState())){

storageDir = new File(Environment.getExternalStorageDirec

"download/");

name - path.substring(path.lastTndexOf(”/”) + 1);

file = new File(storageDir.getPath() , name);

}

//获取 Not if icationManager

this.manager = (NotificationManager)getSystemService

(NOTIFICATION_SERVICE);

this.notification = new Not;

//设置下载的过程中单击通知栏，返回到主界面

intent = new Intent(this, TestDownload_lActivity.class);

pendingintent = Pendingintent.getActivity(this/ 0, intent,

Pendingintent ・ FLAG_CANCEL_CURRENT);

〃设置通知栏显示的内容

notification.icon = R.drawable.ic_launcher;

notification. tickerText ="开始下栽";

notification.setLatestEventlnfo(this, name, n0%n, pendingintent);

//发出通知

manager・notify^。, notification)；

new Thread (new DownloadRunnable ()) . star ; //开启下载的銭程

return super.onStartCommand(intent, flags, startld);

}

  通过Handler处理下载的信息，下载完成或失败时，更新通知栏：

private Handler handler = new Handler(){

public void handleMessage(android.os.Message msg) {

switch (msg.what) {

case DOWNLOAD—COMPLETE://下载成功

//铃声提醒

notification.defaults = Notification.DEFAULTJSOUND;

notification.setLatestEventlnfo(DownloadService.this, name,"下

裁完成，单击安装。"，pendingintent);

manager.notify(0, notification);

break;

case DOWNLOAD_FAIL: / /下载失败

notification.setLatestEventlnfo(DownloadService.this, name,

"下载失败”$ pendinglntent); 

_ Android_史务线程介纟目 |i77

manager.notify(0, notification);

break;

default:

break;

}

}；

}；

  实现Runnable接口，当文件大小不为0时，通过Handler的方法sendMessage发送消息：

//下载文件的线程

private class DownloadRunnable implements Runnable{

^Override

public void run() {

Message message = handler.obtainMessage();

message.what = DOWNLOAD_COMPLETE;

try{//文件存储的路径是否存在

if(!storageDir.exists ()){

storageDir.mkdirs();

}

if (! file. exists () ) { //文件是否存在

file.createNewFile();

}

long downloadsize = downloadFile(path, file);

if(downloadSize>0){

//下載成功

handler.sendMessage(message);

}

}catch (Exception e) {

message.what = DOWNLOAD„FAIL;

handler.sendMessage(message);

}

//从网络上下载文件

public long downloadFile(String downloadUrl,File saveFile) throws

IOExcep七ion{

int downloadCount = 0;

int currentsize = 0;

long totalSize = 0;

int updateTotalSize - 0;

HttpURLConnection httpConnection = null;

Inpu七Stream is = null;

FileOutputStream fos = null;

try {

URL url = new URL(downloadUrl);

httpConnection - (HttpURLConnection)url.openConnection();

httpConnection・ setRequestProperty (''User-Agent'S 11 PacificHttpClient");

if(currentsize > 0) {

httpConnection. setRequestProperty ("RANGE", ,,bytes=1' + currentsize + ;

}

httpConnection.setConnectTimeout(10000);

httpConnection.setReadTimeout(20000);

updateTotalSize = httpConnection.getContentLength();

if (httpConnection,getResponseCode() == 404) {

throw new Exception (*'f ail! M);

}

is = httpConnection,get工nputStream();

fos - new FileOutputStream(saveFile, false);

byte buffer[] = new byte[4096];

int readsize = 0;

while((readsize = is.read(buffer)) > 0){

fos•讨rite(buffer, 0, readsize);

totalsize +二 readsize; 

_ . if((downloadCount = 0)||(int) (totalSize*100/updateTotalSize)

-10>downloadCount){

dovmloadCount += 10；

, notification. setLatestEventlnfo (DownloadSexrvice. this,"正在

下載“，(int)totalSxze*100/updateTotalSize+"%", pendingintent)；

I manager・not;i£y(0, notification);

}

} catch (IOException e) {

e.printStackTrace ()；

} catch (Exception e) {

e.printStackTrace()；

} finally {

if (httipConnectiion != null) {

httpConnection.disconnect()；

}

if (is != null) {

is.close();

}

if(fos !- null) {

fos ・ close();

}

}

return totalsize;

}

  (3)Service类和用户权限在AndroidManifest.xml中的声明。

<?xml version="l. 0" encoding=',utf-8,,?>

<manifest xmlns:android^^http://schemas ・android.com/apk/工es/android"

package:="coin. zhy.download"

android:versionCode="1”

android: versionName=11l. 0n >

<uses-sdk android：minSdkVersion=" 8'* />

<uses-permission

android: name= "android. permission.WRITE_EXTERNAL_STORAGE" />

<uses-permission android:name=,1 android.permission.INTERNET"/>

<application

android: icon="@drawab丄e/ic_1aunc：he:r”

android:label=H@string/app_namen >

<activity

android:name=".TestDownload_lActivity"

android:label=H@string/app_name" >

<intent-filter〉

<action android:name="android.intent.action.MAIN" />

<category android:name=,,android.intent.category.LAUNCHER” />

</intent-filter>

</activity>

<service android: name="DownloadService"X/service>

</application>

</manifest>

  至此，下载功能就实现了。如果有多文件一起下载，还需要做相应的处理，在这里就不多做说明了，有兴趣的读者可以自己去实现。