android执行网络操作

本篇我们会介绍连接到网络中涉及的基本任务，监测的网络连接（包括连接更改），并给予用户控制应用程序的网络使用情况。还介绍了如何解析和使用XML数据。

这个类包含一个示例应用程序来说明如何执行常见的网络操作。您可以下载示例（在右边），并用它作为自己的应用程序源代码的可重用代码。本章的重点有三：

1.连接到网络

2.管理网络的使用

3.解析XML数据

一、连接到网络

在mainfest中声明权限，代码如下：

<uses-permissionandroid:name="android.permission.INTERNET"/>
<uses-permissionandroid:name="android.permission.ACCESS_NETWORK_STATE"/>

选择http客户端

大多数联网的Android应用程序使用HTTP来发送和接收数据。Android包括两个HTTP客户:HttpURLConnection HttpClient和Apache。都支持HTTPS,流媒体上传和下载,可配置的超时,IPv6,和连接池。我们建议使用HttpURLConnection目标应用程序。

检查网络连接

在你的应用程序尝试连接到网络,它应该检查是否一个网络连接可用使用getActiveNetworkInfo()和一个()。记住,这个装置可能范围的一个网络,或用户可能已经禁用wi - fi和移动数据访问。

publicvoidmyClickHandler(Viewview){
...
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=connMgr.getActiveNetworkInfo();
if(networkInfo!=null&&networkInfo.isConnected()){
//fetchdata
}else{
//displayerror
}
...
}

在单独线程中执行网络操作

网络操作可以包括不可预测的延迟。为了防止这种导致一个糟糕的用户体验,总是执行网络操作在一个单独的线程。

publicclassHttpExampleActivityextendsActivity{
privatestaticfinalStringDEBUG_TAG="HttpExample";
privateEditTexturlText;
privateTextViewtextView;

@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
urlText=(EditText)findViewById(R.id.myUrl);
textView=(TextView)findViewById(R.id.myText);
}
//Whenuserclicksbutton,callsAsyncTask.
//BeforeattemptingtofetchtheURL,makessurethatthereisanetworkconnection.
publicvoidmyClickHandler(Viewview){
//GetstheURLfromtheUI'stextfield.
StringstringUrl=urlText.getText().toString();
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=connMgr.getActiveNetworkInfo();
if(networkInfo!=null&&networkInfo.isConnected()){
newDownloadWebpageText().execute(stringUrl);
}else{
textView.setText("Nonetworkconnectionavailable.");
}
}
//UsesAsyncTasktocreateataskawayfromthemainUIthread.Thistasktakesa
//URLstringandusesittocreateanHttpUrlConnection.Oncetheconnection
//hasbeenestablished,theAsyncTaskdownloadsthecontentsofthewebpageas
//anInputStream.Finally,theInputStreamisconvertedintoastring,whichis
//displayedintheUIbytheAsyncTask'sonPostExecutemethod.
privateclassDownloadWebpageTextextendsAsyncTask{
@Override
protectedStringdoInBackground(String...urls){

//paramscomesfromtheexecute()call:params[0]istheurl.
try{
returndownloadUrl(urls[0]);
}catch(IOExceptione){
return"Unabletoretrievewebpage.URLmaybeinvalid.";
}
}
//onPostExecutedisplaystheresultsoftheAsyncTask.
@Override
protectedvoidonPostExecute(Stringresult){
textView.setText(result);
}
}
...
}

连接和下载数据

在你的线程执行您的网络交易,你可以使用HttpURLConnection来执行一个GET和下载数据。在您调用connect(),你可以得到一个InputStream的数据通过调用getInputStream()。

//GivenaURL,establishesanHttpUrlConnectionandretrieves
//thewebpagecontentasaInputStream,whichitreturnsas
//astring.
privateStringdownloadUrl(Stringmyurl)throwsIOException{
InputStreamis=null;
//Onlydisplaythefirst500charactersoftheretrieved
//webpagecontent.
intlen=500;

try{
URLurl=newURL(myurl);
HttpURLConnectionconn=(HttpURLConnection)url.openConnection();
conn.setReadTimeout(10000/*milliseconds*/);
conn.setConnectTimeout(15000/*milliseconds*/);
conn.setRequestMethod("GET");
conn.setDoInput(true);
//Startsthequery
conn.connect();
intresponse=conn.getResponseCode();
Log.d(DEBUG_TAG,"Theresponseis:"+response);
is=conn.getInputStream();
//ConverttheInputStreamintoastring
StringcontentAsString=readIt(is,len);
returncontentAsString;

//MakessurethattheInputStreamisclosedaftertheappis
//finishedusingit.
}finally{
if(is!=null){
is.close();
}
}
}

getResponseCode()返回连接的状态码。这是一种有用的方式获得一些额外的信息的连接。一个200的状态代码表示成功。

转换InputStream到String

//ReadsanInputStreamandconvertsittoaString.
publicStringreadIt(InputStreamstream,intlen)throwsIOException,UnsupportedEncodingException{
Readerreader=null;
reader=newInputStreamReader(stream,"UTF-8");
char[]buffer=newchar[len];
reader.read(buffer);
returnnewString(buffer);
}

二、管理网络

检查设备的网络连接

一个设备可以有各种类型的网络连接。这节课的重点是使用wi - fi或手机或网络连接，这个代码片段测试网络连接wi - fi和移动。它确定这些网络接口是可用的或连接的(即网络连接是否存在,如果可以建立套接字和传递数据)

privatestaticfinalStringDEBUG_TAG="NetworkStatusExample";
...
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
booleanisWifiConn=networkInfo.isConnected();
networkInfo=connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
booleanisMobileConn=networkInfo.isConnected();
Log.d(DEBUG_TAG,"Wificonnected:"+isWifiConn);
Log.d(DEBUG_TAG,"Mobileconnected:"+isMobileConn);

管理网络的使用

您可以实现一个首选项活动,让用户明确控制应用程序的使用网络资源。例如:1.你可能允许用户上传的视频只有当设备被连接到wi - fi网络。2.你可能会同步(或没有)根据特定标准如网络可用性、时间间隔,等等。

编写一个应用程序,支持网络访问和管理网络的使用,你的清单必须有正确的权限和意图过滤器。

在样例应用程序中,这个规定了SettingsActivity,将显示一个UI让用户知道何时可以进行下载操作。

<?xmlversion="1.0"encoding="utf-8"?>
<manifestxmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.networkusage"
...>
<uses-sdkandroid:minSdkVersion="4"
android:targetSdkVersion="14"/>

<uses-permissionandroid:name="android.permission.INTERNET"/>
<uses-permissionandroid:name="android.permission.ACCESS_NETWORK_STATE"/>
<application
...>
...
<activityandroid:label="SettingsActivity"android:name=".SettingsActivity">
<intent-filter>
<actionandroid:name="android.intent.action.MANAGE_NETWORK_USAGE"/>
<categoryandroid:name="android.intent.category.DEFAULT"/>
</intent-filter>
</activity>
</application>
</manifest>

publicclassSettingsActivityextendsPreferenceActivityimplementsOnSharedPreferenceChangeListener{

@Override
protectedvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);

//LoadstheXMLpreferencesfile
addPreferencesFromResource(R.xml.preferences);
}

@Override
protectedvoidonResume(){
super.onResume();
//Registersalistenerwheneverakeychanges
getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
}

@Override
protectedvoidonPause(){
super.onPause();
//UnregistersthelistenersetinonResume().
//It'sbestpracticetounregisterlistenerswhenyourappisn'tusingthemtocutdownon
//unnecessarysystemoverhead.YoudothisinonPause().
getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
}

//Whentheuserchangesthepreferencesselection,
//onSharedPreferenceChanged()restartsthemainactivityasanew
//task.SetsthetherefreshDisplayflagto"true"toindicatethat
//themainactivityshouldupdateitsdisplay.
//ThemainactivityqueriesthePreferenceManagertogetthelatestsettings.

@Override
publicvoidonSharedPreferenceChanged(SharedPreferencessharedPreferences,Stringkey){
//SetsrefreshDisplaytotruesothatwhentheuserreturnstothemain
//activity,thedisplayrefreshestoreflectthenewsettings.
NetworkActivity.refreshDisplay=true;
}
}

响应网络变动

如果有一个匹配发生在设置和设备的网络连接(例如,如果设置为“wi - fi”和设备有一个wi - fi连接)之间,应用程序下载提继续并刷新显示

publicclassNetworkActivityextendsActivity{
publicstaticfinalStringWIFI="Wi-Fi";
publicstaticfinalStringANY="Any";
privatestaticfinalStringURL="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest";

//WhetherthereisaWi-Ficonnection.
privatestaticbooleanwifiConnected=false;
//Whetherthereisamobileconnection.
privatestaticbooleanmobileConnected=false;
//Whetherthedisplayshouldberefreshed.
publicstaticbooleanrefreshDisplay=true;

//Theuser'scurrentnetworkpreferencesetting.
publicstaticStringsPref=null;

//TheBroadcastReceiverthattracksnetworkconnectivitychanges.
privateNetworkReceiverreceiver=newNetworkReceiver();

@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);

//RegistersBroadcastReceivertotracknetworkconnectionchanges.
IntentFilterfilter=newIntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
receiver=newNetworkReceiver();
this.registerReceiver(receiver,filter);
}

@Override
publicvoidonDestroy(){
super.onDestroy();
//UnregistersBroadcastReceiverwhenappisdestroyed.
if(receiver!=null){
this.unregisterReceiver(receiver);
}
}

//Refreshesthedisplayifthenetworkconnectionandthe
//prefsettingsallowit.

@Override
publicvoidonStart(){
super.onStart();

//Getstheuser'snetworkpreferencesettings
SharedPreferencessharedPrefs=PreferenceManager.getDefaultSharedPreferences(this);

//Retrievesastringvalueforthepreferences.Thesecondparameter
//isthedefaultvaluetouseifapreferencevalueisnotfound.
sPref=sharedPrefs.getString("listPref","Wi-Fi");
updateConnectedFlags();

if(refreshDisplay){
loadPage();
}
}

//ChecksthenetworkconnectionandsetsthewifiConnectedandmobileConnected
//variablesaccordingly.
publicvoidupdateConnectedFlags(){
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);

NetworkInfoactiveInfo=connMgr.getActiveNetworkInfo();
if(activeInfo!=null&&activeInfo.isConnected()){
wifiConnected=activeInfo.getType()==ConnectivityManager.TYPE_WIFI;
mobileConnected=activeInfo.getType()==ConnectivityManager.TYPE_MOBILE;
}else{
wifiConnected=false;
mobileConnected=false;
}
}

//UsesAsyncTasksubclasstodownloadtheXMLfeedfromstackoverflow.com.
publicvoidloadPage(){
if(((sPref.equals(ANY))&&(wifiConnected||mobileConnected))
||((sPref.equals(WIFI))&&(wifiConnected))){
//AsyncTasksubclass
newDownloadXmlTask().execute(URL);
}else{
showErrorPage();
}
}
...

}

检测网络连接变化

publicclassNetworkReceiverextendsBroadcastReceiver{

@Override
publicvoidonReceive(Contextcontext,Intentintent){
ConnectivityManagerconn=(ConnectivityManager)
context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=conn.getActiveNetworkInfo();

//Checkstheuserprefsandthenetworkconnection.Basedontheresult,decideswhether
//torefreshthedisplayorkeepthecurrentdisplay.
//IftheuserprefisWi-Fionly,checkstoseeifthedevicehasaWi-Ficonnection.
if(WIFI.equals(sPref)&&networkInfo!=null&&networkInfo.getType()==ConnectivityManager.TYPE_WIFI){
//IfdevicehasitsWi-Ficonnection,setsrefreshDisplay
//totrue.Thiscausesthedisplaytoberefreshedwhentheuser
//returnstotheapp.
refreshDisplay=true;
Toast.makeText(context,R.string.wifi_connected,Toast.LENGTH_SHORT).show();
//IfthesettingisANYnetworkandthereisanetworkconnection
//(whichbyprocessofeliminationwouldbemobile),setsrefreshDisplaytotrue.
}elseif(ANY.equals(sPref)&&networkInfo!=null){
refreshDisplay=true;

//Otherwise,theappcan'tdownloadcontent--eitherbecausethereisnonetwork
//connection(mobileorWi-Fi),orbecausetheprefsettingisWIFI,andthere
//isnoWi-Ficonnection.
//SetsrefreshDisplaytofalse.
}else{
refreshDisplay=false;
Toast.makeText(context,R.string.lost_connection,Toast.LENGTH_SHORT).show();
}
}

三、解析xml

上传和解析XML数据是很常见的任务,网络连接应用程序。这一课解释了如何解析XML文档并使用他们的数据

选择转换器

我们建议XmlPullParser,这是一种高效且可维护的方式来解析XML在Android里。

分析需求

<?xmlversion="1.0"encoding="utf-8"?>
<feedxmlns="http://www.w3.org/2005/Atom"xmlns:creativeCommons="http://backend.userland.com/creativeCommonsRssModule"...">
<titletype="text">newestquestionstaggedandroid-StackOverflow</title>
...
<entry>
...
</entry>
<entry>
<id>http://stackoverflow.com/q/9439999</id>
<re:rankscheme="http://stackoverflow.com">0</re:rank>
<titletype="text">Whereismydatafile?</title>
<categoryscheme="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest/tags"term="android"/>
<categoryscheme="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest/tags"term="file"/>
<author>
<name>cliff2310</name>
<uri>http://stackoverflow.com/users/1128925</uri>
</author>
<linkrel="alternate"href="http://stackoverflow.com/questions/9439999/where-is-my-data-file"/>
<published>2012-02-25T00:30:54Z</published>
<updated>2012-02-25T00:30:54Z</updated>
<summarytype="html">
<p>IhaveanApplicationthatrequiresadatafile...</p>
</summary>
</entry>
<entry>
...
</entry>
...
</feed>

实例化转化器

publicclassStackOverflowXmlParser{
//Wedon'tusenamespaces
privatestaticfinalStringns=null;

publicListparse(InputStreamin)throwsXmlPullParserException,IOException{
try{
XmlPullParserparser=Xml.newPullParser();
parser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES,false);
parser.setInput(in,null);
parser.nextTag();
returnreadFeed(parser);
}finally{
in.close();
}
}
...
}
读取xml
privateListreadFeed(XmlPullParserparser)throwsXmlPullParserException,IOException{
Listentries=newArrayList();
parser.require(XmlPullParser.START_TAG,ns,"feed");
while(parser.next()!=XmlPullParser.END_TAG){
if(parser.getEventType()!=XmlPullParser.START_TAG){
continue;
}
Stringname=parser.getName();
//Startsbylookingfortheentrytag
if(name.equals("entry")){
entries.add(readEntry(parser));
}else{
skip(parser);
}
}
returnentries;
}

下面这个代码片段展示了如何解析器解析条目、标题、链接和总结：

publicstaticclassEntry{
publicfinalStringtitle;
publicfinalStringlink;
publicfinalStringsummary;
privateEntry(Stringtitle,Stringsummary,Stringlink){
this.title=title;
this.summary=summary;
this.link=link;
}
}

//Parsesthecontentsofanentry.Ifitencountersatitle,summary,orlinktag,handsthemoff
//totheirrespective"read"methodsforprocessing.Otherwise,skipsthetag.
privateEntryreadEntry(XmlPullParserparser)throwsXmlPullParserException,IOException{
parser.require(XmlPullParser.START_TAG,ns,"entry");
Stringtitle=null;
Stringsummary=null;
Stringlink=null;
while(parser.next()!=XmlPullParser.END_TAG){
if(parser.getEventType()!=XmlPullParser.START_TAG){
continue;
}
Stringname=parser.getName();
if(name.equals("title")){
title=readTitle(parser);
}elseif(name.equals("summary")){
summary=readSummary(parser);
}elseif(name.equals("link")){
link=readLink(parser);
}else{
skip(parser);
}
}
returnnewEntry(title,summary,link);
}
//Processestitletagsinthefeed.
privateStringreadTitle(XmlPullParserparser)throwsIOException,XmlPullParserException{
parser.require(XmlPullParser.START_TAG,ns,"title");
Stringtitle=readText(parser);
parser.require(XmlPullParser.END_TAG,ns,"title");
returntitle;
}

//Processeslinktagsinthefeed.
privateStringreadLink(XmlPullParserparser)throwsIOException,XmlPullParserException{
Stringlink="";
parser.require(XmlPullParser.START_TAG,ns,"link");
Stringtag=parser.getName();
StringrelType=parser.getAttributeValue(null,"rel");
if(tag.equals("link")){
if(relType.equals("alternate")){
link=parser.getAttributeValue(null,"href");
parser.nextTag();
}
}
parser.require(XmlPullParser.END_TAG,ns,"link");
returnlink;
}
//Processessummarytagsinthefeed.
privateStringreadSummary(XmlPullParserparser)throwsIOException,XmlPullParserException{
parser.require(XmlPullParser.START_TAG,ns,"summary");
Stringsummary=readText(parser);
parser.require(XmlPullParser.END_TAG,ns,"summary");
returnsummary;
}
//Forthetagstitleandsummary,extractstheirtextvalues.
privateStringreadText(XmlPullParserparser)throwsIOException,XmlPullParserException{
Stringresult="";
if(parser.next()==XmlPullParser.TEXT){
result=parser.getText();
parser.nextTag();
}
returnresult;
}
...
}

跳过无用的标签

privatevoidskip(XmlPullParserparser)throwsXmlPullParserException,IOException{
if(parser.getEventType()!=XmlPullParser.START_TAG){
thrownewIllegalStateException();
}
intdepth=1;
while(depth!=0){
switch(parser.next()){
caseXmlPullParser.END_TAG:
depth--;
break;
caseXmlPullParser.START_TAG:
depth++;
break;
}
}
}

使用xml数据

publicclassNetworkActivityextendsActivity{
publicstaticfinalStringWIFI="Wi-Fi";
publicstaticfinalStringANY="Any";
privatestaticfinalStringURL="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest";

//WhetherthereisaWi-Ficonnection.
privatestaticbooleanwifiConnected=false;
//Whetherthereisamobileconnection.
privatestaticbooleanmobileConnected=false;
//Whetherthedisplayshouldberefreshed.
publicstaticbooleanrefreshDisplay=true;
publicstaticStringsPref=null;
...

//UsesAsyncTasktodownloadtheXMLfeedfromstackoverflow.com.
publicvoidloadPage(){

if((sPref.equals(ANY))&&(wifiConnected||mobileConnected)){
newDownloadXmlTask().execute(URL);
}
elseif((sPref.equals(WIFI))&&(wifiConnected)){
newDownloadXmlTask().execute(URL);
}else{
//showerror
}
}

动态下载xml

//ImplementationofAsyncTaskusedtodownloadXMLfeedfromstackoverflow.com.
privateclassDownloadXmlTaskextendsAsyncTask<String,Void,String>{
@Override
protectedStringdoInBackground(String...urls){
try{
returnloadXmlFromNetwork(urls[0]);
}catch(IOExceptione){
returngetResources().getString(R.string.connection_error);
}catch(XmlPullParserExceptione){
returngetResources().getString(R.string.xml_error);
}
}
@Override
protectedvoidonPostExecute(Stringresult){
setContentView(R.layout.main);
//DisplaystheHTMLstringintheUIviaaWebView
WebViewmyWebView=(WebView)findViewById(R.id.webview);
myWebView.loadData(result,"text/html",null);
}
}

加载xml

//UploadsXMLfromstackoverflow.com,parsesit,andcombinesitwith
//HTMLmarkup.ReturnsHTMLstring.
privateStringloadXmlFromNetwork(StringurlString)throwsXmlPullParserException,IOException{
InputStreamstream=null;
//Instantiatetheparser
StackOverflowXmlParserstackOverflowXmlParser=newStackOverflowXmlParser();
List<Entry>entries=null;
Stringtitle=null;
Stringurl=null;
Stringsummary=null;
CalendarrightNow=Calendar.getInstance();
DateFormatformatter=newSimpleDateFormat("MMMddh:mmaa");

//Checkswhethertheusersetthepreferencetoincludesummarytext
SharedPreferencessharedPrefs=PreferenceManager.getDefaultSharedPreferences(this);
booleanpref=sharedPrefs.getBoolean("summaryPref",false);

StringBuilderhtmlString=newStringBuilder();
htmlString.append("<h3>"+getResources().getString(R.string.page_title)+"</h3>");
htmlString.append("<em>"+getResources().getString(R.string.updated)+""+
formatter.format(rightNow.getTime())+"</em>");

try{
stream=downloadUrl(urlString);
entries=stackOverflowXmlParser.parse(stream);
//MakessurethattheInputStreamisclosedaftertheappis
//finishedusingit.
}finally{
if(stream!=null){
stream.close();
}
}

//StackOverflowXmlParserreturnsaList(called"entries")ofEntryobjects.
//EachEntryobjectrepresentsasinglepostintheXMLfeed.
//ThissectionprocessestheentrieslisttocombineeachentrywithHTMLmarkup.
//EachentryisdisplayedintheUIasalinkthatoptionallyincludes
//atextsummary.
for(Entryentry:entries){
htmlString.append("<p><ahref='");
htmlString.append(entry.link);
htmlString.append("'>"+entry.title+"</a></p>");
//Iftheusersetthepreferencetoincludesummarytext,
//addsittothedisplay.
if(pref){
htmlString.append(entry.summary);
}
}
returnhtmlString.toString();
}
//GivenastringrepresentationofaURL,setsupaconnectionandgets
//aninputstream.
privateInputStreamdownloadUrl(StringurlString)throwsIOException{
URLurl=newURL(urlString);
HttpURLConnectionconn=(HttpURLConnection)url.openConnection();
conn.setReadTimeout(10000/*milliseconds*/);
conn.setConnectTimeout(15000/*milliseconds*/);
conn.setRequestMethod("GET");
conn.setDoInput(true);
//Startsthequery
conn.connect();
InputStreamstream=conn.getInputStream();
}

上面的片段代码为了帮助大家理解，这里还是老习惯，贴上项目的源代码，本来是有项目截图，运行效果图之类的图的，只是这篇文章太长了，再弄图片，就更占篇幅了，所以就只贴源码了，大家可以自己的运行起来看看，希望能从整体的架构和具体的代码细节上帮助到大家。

本篇我们会介绍连接到网络中涉及的基本任务，监测的网络连接（包括连接更改），并给予用户控制应用程序的网络使用情况。还介绍了如何解析和使用XML数据。

这个类包含一个示例应用程序来说明如何执行常见的网络操作。您可以下载示例（在右边），并用它作为自己的应用程序源代码的可重用代码。本章的重点有三：

1.连接到网络

2.管理网络的使用

3.解析XML数据

一、连接到网络

在mainfest中声明权限，代码如下：

<uses-permissionandroid:name="android.permission.INTERNET"/>
<uses-permissionandroid:name="android.permission.ACCESS_NETWORK_STATE"/>

选择http客户端

大多数联网的Android应用程序使用HTTP来发送和接收数据。Android包括两个HTTP客户:HttpURLConnection HttpClient和Apache。都支持HTTPS,流媒体上传和下载,可配置的超时,IPv6,和连接池。我们建议使用HttpURLConnection目标应用程序。

检查网络连接

在你的应用程序尝试连接到网络,它应该检查是否一个网络连接可用使用getActiveNetworkInfo()和一个()。记住,这个装置可能范围的一个网络,或用户可能已经禁用wi - fi和移动数据访问。

publicvoidmyClickHandler(Viewview){
...
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=connMgr.getActiveNetworkInfo();
if(networkInfo!=null&&networkInfo.isConnected()){
//fetchdata
}else{
//displayerror
}
...
}

在单独线程中执行网络操作

网络操作可以包括不可预测的延迟。为了防止这种导致一个糟糕的用户体验,总是执行网络操作在一个单独的线程。

publicclassHttpExampleActivityextendsActivity{
privatestaticfinalStringDEBUG_TAG="HttpExample";
privateEditTexturlText;
privateTextViewtextView;

@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
urlText=(EditText)findViewById(R.id.myUrl);
textView=(TextView)findViewById(R.id.myText);
}
//Whenuserclicksbutton,callsAsyncTask.
//BeforeattemptingtofetchtheURL,makessurethatthereisanetworkconnection.
publicvoidmyClickHandler(Viewview){
//GetstheURLfromtheUI'stextfield.
StringstringUrl=urlText.getText().toString();
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=connMgr.getActiveNetworkInfo();
if(networkInfo!=null&&networkInfo.isConnected()){
newDownloadWebpageText().execute(stringUrl);
}else{
textView.setText("Nonetworkconnectionavailable.");
}
}
//UsesAsyncTasktocreateataskawayfromthemainUIthread.Thistasktakesa
//URLstringandusesittocreateanHttpUrlConnection.Oncetheconnection
//hasbeenestablished,theAsyncTaskdownloadsthecontentsofthewebpageas
//anInputStream.Finally,theInputStreamisconvertedintoastring,whichis
//displayedintheUIbytheAsyncTask'sonPostExecutemethod.
privateclassDownloadWebpageTextextendsAsyncTask{
@Override
protectedStringdoInBackground(String...urls){

//paramscomesfromtheexecute()call:params[0]istheurl.
try{
returndownloadUrl(urls[0]);
}catch(IOExceptione){
return"Unabletoretrievewebpage.URLmaybeinvalid.";
}
}
//onPostExecutedisplaystheresultsoftheAsyncTask.
@Override
protectedvoidonPostExecute(Stringresult){
textView.setText(result);
}
}
...
}

连接和下载数据

在你的线程执行您的网络交易,你可以使用HttpURLConnection来执行一个GET和下载数据。在您调用connect(),你可以得到一个InputStream的数据通过调用getInputStream()。

//GivenaURL,establishesanHttpUrlConnectionandretrieves
//thewebpagecontentasaInputStream,whichitreturnsas
//astring.
privateStringdownloadUrl(Stringmyurl)throwsIOException{
InputStreamis=null;
//Onlydisplaythefirst500charactersoftheretrieved
//webpagecontent.
intlen=500;

try{
URLurl=newURL(myurl);
HttpURLConnectionconn=(HttpURLConnection)url.openConnection();
conn.setReadTimeout(10000/*milliseconds*/);
conn.setConnectTimeout(15000/*milliseconds*/);
conn.setRequestMethod("GET");
conn.setDoInput(true);
//Startsthequery
conn.connect();
intresponse=conn.getResponseCode();
Log.d(DEBUG_TAG,"Theresponseis:"+response);
is=conn.getInputStream();
//ConverttheInputStreamintoastring
StringcontentAsString=readIt(is,len);
returncontentAsString;

//MakessurethattheInputStreamisclosedaftertheappis
//finishedusingit.
}finally{
if(is!=null){
is.close();
}
}
}

getResponseCode()返回连接的状态码。这是一种有用的方式获得一些额外的信息的连接。一个200的状态代码表示成功。

转换InputStream到String

//ReadsanInputStreamandconvertsittoaString.
publicStringreadIt(InputStreamstream,intlen)throwsIOException,UnsupportedEncodingException{
Readerreader=null;
reader=newInputStreamReader(stream,"UTF-8");
char[]buffer=newchar[len];
reader.read(buffer);
returnnewString(buffer);
}

二、管理网络

检查设备的网络连接

一个设备可以有各种类型的网络连接。这节课的重点是使用wi - fi或手机或网络连接，这个代码片段测试网络连接wi - fi和移动。它确定这些网络接口是可用的或连接的(即网络连接是否存在,如果可以建立套接字和传递数据)

privatestaticfinalStringDEBUG_TAG="NetworkStatusExample";
...
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=connMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
booleanisWifiConn=networkInfo.isConnected();
networkInfo=connMgr.getNetworkInfo(ConnectivityManager.TYPE_MOBILE);
booleanisMobileConn=networkInfo.isConnected();
Log.d(DEBUG_TAG,"Wificonnected:"+isWifiConn);
Log.d(DEBUG_TAG,"Mobileconnected:"+isMobileConn);

管理网络的使用

您可以实现一个首选项活动,让用户明确控制应用程序的使用网络资源。例如:1.你可能允许用户上传的视频只有当设备被连接到wi - fi网络。2.你可能会同步(或没有)根据特定标准如网络可用性、时间间隔,等等。

编写一个应用程序,支持网络访问和管理网络的使用,你的清单必须有正确的权限和意图过滤器。

在样例应用程序中,这个规定了SettingsActivity,将显示一个UI让用户知道何时可以进行下载操作。

<?xmlversion="1.0"encoding="utf-8"?>
<manifestxmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.networkusage"
...>
<uses-sdkandroid:minSdkVersion="4"
android:targetSdkVersion="14"/>

<uses-permissionandroid:name="android.permission.INTERNET"/>
<uses-permissionandroid:name="android.permission.ACCESS_NETWORK_STATE"/>
<application
...>
...
<activityandroid:label="SettingsActivity"android:name=".SettingsActivity">
<intent-filter>
<actionandroid:name="android.intent.action.MANAGE_NETWORK_USAGE"/>
<categoryandroid:name="android.intent.category.DEFAULT"/>
</intent-filter>
</activity>
</application>
</manifest>

publicclassSettingsActivityextendsPreferenceActivityimplementsOnSharedPreferenceChangeListener{

@Override
protectedvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);

//LoadstheXMLpreferencesfile
addPreferencesFromResource(R.xml.preferences);
}

@Override
protectedvoidonResume(){
super.onResume();
//Registersalistenerwheneverakeychanges
getPreferenceScreen().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
}

@Override
protectedvoidonPause(){
super.onPause();
//UnregistersthelistenersetinonResume().
//It'sbestpracticetounregisterlistenerswhenyourappisn'tusingthemtocutdownon
//unnecessarysystemoverhead.YoudothisinonPause().
getPreferenceScreen().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
}

//Whentheuserchangesthepreferencesselection,
//onSharedPreferenceChanged()restartsthemainactivityasanew
//task.SetsthetherefreshDisplayflagto"true"toindicatethat
//themainactivityshouldupdateitsdisplay.
//ThemainactivityqueriesthePreferenceManagertogetthelatestsettings.

@Override
publicvoidonSharedPreferenceChanged(SharedPreferencessharedPreferences,Stringkey){
//SetsrefreshDisplaytotruesothatwhentheuserreturnstothemain
//activity,thedisplayrefreshestoreflectthenewsettings.
NetworkActivity.refreshDisplay=true;
}
}

响应网络变动

如果有一个匹配发生在设置和设备的网络连接(例如,如果设置为“wi - fi”和设备有一个wi - fi连接)之间,应用程序下载提继续并刷新显示

publicclassNetworkActivityextendsActivity{
publicstaticfinalStringWIFI="Wi-Fi";
publicstaticfinalStringANY="Any";
privatestaticfinalStringURL="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest";

//WhetherthereisaWi-Ficonnection.
privatestaticbooleanwifiConnected=false;
//Whetherthereisamobileconnection.
privatestaticbooleanmobileConnected=false;
//Whetherthedisplayshouldberefreshed.
publicstaticbooleanrefreshDisplay=true;

//Theuser'scurrentnetworkpreferencesetting.
publicstaticStringsPref=null;

//TheBroadcastReceiverthattracksnetworkconnectivitychanges.
privateNetworkReceiverreceiver=newNetworkReceiver();

@Override
publicvoidonCreate(BundlesavedInstanceState){
super.onCreate(savedInstanceState);

//RegistersBroadcastReceivertotracknetworkconnectionchanges.
IntentFilterfilter=newIntentFilter(ConnectivityManager.CONNECTIVITY_ACTION);
receiver=newNetworkReceiver();
this.registerReceiver(receiver,filter);
}

@Override
publicvoidonDestroy(){
super.onDestroy();
//UnregistersBroadcastReceiverwhenappisdestroyed.
if(receiver!=null){
this.unregisterReceiver(receiver);
}
}

//Refreshesthedisplayifthenetworkconnectionandthe
//prefsettingsallowit.

@Override
publicvoidonStart(){
super.onStart();

//Getstheuser'snetworkpreferencesettings
SharedPreferencessharedPrefs=PreferenceManager.getDefaultSharedPreferences(this);

//Retrievesastringvalueforthepreferences.Thesecondparameter
//isthedefaultvaluetouseifapreferencevalueisnotfound.
sPref=sharedPrefs.getString("listPref","Wi-Fi");
updateConnectedFlags();

if(refreshDisplay){
loadPage();
}
}

//ChecksthenetworkconnectionandsetsthewifiConnectedandmobileConnected
//variablesaccordingly.
publicvoidupdateConnectedFlags(){
ConnectivityManagerconnMgr=(ConnectivityManager)
getSystemService(Context.CONNECTIVITY_SERVICE);

NetworkInfoactiveInfo=connMgr.getActiveNetworkInfo();
if(activeInfo!=null&&activeInfo.isConnected()){
wifiConnected=activeInfo.getType()==ConnectivityManager.TYPE_WIFI;
mobileConnected=activeInfo.getType()==ConnectivityManager.TYPE_MOBILE;
}else{
wifiConnected=false;
mobileConnected=false;
}
}

//UsesAsyncTasksubclasstodownloadtheXMLfeedfromstackoverflow.com.
publicvoidloadPage(){
if(((sPref.equals(ANY))&&(wifiConnected||mobileConnected))
||((sPref.equals(WIFI))&&(wifiConnected))){
//AsyncTasksubclass
newDownloadXmlTask().execute(URL);
}else{
showErrorPage();
}
}
...

}

检测网络连接变化

publicclassNetworkReceiverextendsBroadcastReceiver{

@Override
publicvoidonReceive(Contextcontext,Intentintent){
ConnectivityManagerconn=(ConnectivityManager)
context.getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfonetworkInfo=conn.getActiveNetworkInfo();

//Checkstheuserprefsandthenetworkconnection.Basedontheresult,decideswhether
//torefreshthedisplayorkeepthecurrentdisplay.
//IftheuserprefisWi-Fionly,checkstoseeifthedevicehasaWi-Ficonnection.
if(WIFI.equals(sPref)&&networkInfo!=null&&networkInfo.getType()==ConnectivityManager.TYPE_WIFI){
//IfdevicehasitsWi-Ficonnection,setsrefreshDisplay
//totrue.Thiscausesthedisplaytoberefreshedwhentheuser
//returnstotheapp.
refreshDisplay=true;
Toast.makeText(context,R.string.wifi_connected,Toast.LENGTH_SHORT).show();
//IfthesettingisANYnetworkandthereisanetworkconnection
//(whichbyprocessofeliminationwouldbemobile),setsrefreshDisplaytotrue.
}elseif(ANY.equals(sPref)&&networkInfo!=null){
refreshDisplay=true;

//Otherwise,theappcan'tdownloadcontent--eitherbecausethereisnonetwork
//connection(mobileorWi-Fi),orbecausetheprefsettingisWIFI,andthere
//isnoWi-Ficonnection.
//SetsrefreshDisplaytofalse.
}else{
refreshDisplay=false;
Toast.makeText(context,R.string.lost_connection,Toast.LENGTH_SHORT).show();
}
}

三、解析xml

上传和解析XML数据是很常见的任务,网络连接应用程序。这一课解释了如何解析XML文档并使用他们的数据

选择转换器

我们建议XmlPullParser,这是一种高效且可维护的方式来解析XML在Android里。

分析需求

<?xmlversion="1.0"encoding="utf-8"?>
<feedxmlns="http://www.w3.org/2005/Atom"xmlns:creativeCommons="http://backend.userland.com/creativeCommonsRssModule"...">
<titletype="text">newestquestionstaggedandroid-StackOverflow</title>
...
<entry>
...
</entry>
<entry>
<id>http://stackoverflow.com/q/9439999</id>
<re:rankscheme="http://stackoverflow.com">0</re:rank>
<titletype="text">Whereismydatafile?</title>
<categoryscheme="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest/tags"term="android"/>
<categoryscheme="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest/tags"term="file"/>
<author>
<name>cliff2310</name>
<uri>http://stackoverflow.com/users/1128925</uri>
</author>
<linkrel="alternate"href="http://stackoverflow.com/questions/9439999/where-is-my-data-file"/>
<published>2012-02-25T00:30:54Z</published>
<updated>2012-02-25T00:30:54Z</updated>
<summarytype="html">
<p>IhaveanApplicationthatrequiresadatafile...</p>
</summary>
</entry>
<entry>
...
</entry>
...
</feed>

实例化转化器

publicclassStackOverflowXmlParser{
//Wedon'tusenamespaces
privatestaticfinalStringns=null;

publicListparse(InputStreamin)throwsXmlPullParserException,IOException{
try{
XmlPullParserparser=Xml.newPullParser();
parser.setFeature(XmlPullParser.FEATURE_PROCESS_NAMESPACES,false);
parser.setInput(in,null);
parser.nextTag();
returnreadFeed(parser);
}finally{
in.close();
}
}
...
}
读取xml
privateListreadFeed(XmlPullParserparser)throwsXmlPullParserException,IOException{
Listentries=newArrayList();
parser.require(XmlPullParser.START_TAG,ns,"feed");
while(parser.next()!=XmlPullParser.END_TAG){
if(parser.getEventType()!=XmlPullParser.START_TAG){
continue;
}
Stringname=parser.getName();
//Startsbylookingfortheentrytag
if(name.equals("entry")){
entries.add(readEntry(parser));
}else{
skip(parser);
}
}
returnentries;
}

下面这个代码片段展示了如何解析器解析条目、标题、链接和总结：

publicstaticclassEntry{
publicfinalStringtitle;
publicfinalStringlink;
publicfinalStringsummary;
privateEntry(Stringtitle,Stringsummary,Stringlink){
this.title=title;
this.summary=summary;
this.link=link;
}
}

//Parsesthecontentsofanentry.Ifitencountersatitle,summary,orlinktag,handsthemoff
//totheirrespective"read"methodsforprocessing.Otherwise,skipsthetag.
privateEntryreadEntry(XmlPullParserparser)throwsXmlPullParserException,IOException{
parser.require(XmlPullParser.START_TAG,ns,"entry");
Stringtitle=null;
Stringsummary=null;
Stringlink=null;
while(parser.next()!=XmlPullParser.END_TAG){
if(parser.getEventType()!=XmlPullParser.START_TAG){
continue;
}
Stringname=parser.getName();
if(name.equals("title")){
title=readTitle(parser);
}elseif(name.equals("summary")){
summary=readSummary(parser);
}elseif(name.equals("link")){
link=readLink(parser);
}else{
skip(parser);
}
}
returnnewEntry(title,summary,link);
}
//Processestitletagsinthefeed.
privateStringreadTitle(XmlPullParserparser)throwsIOException,XmlPullParserException{
parser.require(XmlPullParser.START_TAG,ns,"title");
Stringtitle=readText(parser);
parser.require(XmlPullParser.END_TAG,ns,"title");
returntitle;
}

//Processeslinktagsinthefeed.
privateStringreadLink(XmlPullParserparser)throwsIOException,XmlPullParserException{
Stringlink="";
parser.require(XmlPullParser.START_TAG,ns,"link");
Stringtag=parser.getName();
StringrelType=parser.getAttributeValue(null,"rel");
if(tag.equals("link")){
if(relType.equals("alternate")){
link=parser.getAttributeValue(null,"href");
parser.nextTag();
}
}
parser.require(XmlPullParser.END_TAG,ns,"link");
returnlink;
}
//Processessummarytagsinthefeed.
privateStringreadSummary(XmlPullParserparser)throwsIOException,XmlPullParserException{
parser.require(XmlPullParser.START_TAG,ns,"summary");
Stringsummary=readText(parser);
parser.require(XmlPullParser.END_TAG,ns,"summary");
returnsummary;
}
//Forthetagstitleandsummary,extractstheirtextvalues.
privateStringreadText(XmlPullParserparser)throwsIOException,XmlPullParserException{
Stringresult="";
if(parser.next()==XmlPullParser.TEXT){
result=parser.getText();
parser.nextTag();
}
returnresult;
}
...
}

跳过无用的标签

privatevoidskip(XmlPullParserparser)throwsXmlPullParserException,IOException{
if(parser.getEventType()!=XmlPullParser.START_TAG){
thrownewIllegalStateException();
}
intdepth=1;
while(depth!=0){
switch(parser.next()){
caseXmlPullParser.END_TAG:
depth--;
break;
caseXmlPullParser.START_TAG:
depth++;
break;
}
}
}

使用xml数据

publicclassNetworkActivityextendsActivity{
publicstaticfinalStringWIFI="Wi-Fi";
publicstaticfinalStringANY="Any";
privatestaticfinalStringURL="http://stackoverflow.com/feeds/tag?tagnames=android&sort=newest";

//WhetherthereisaWi-Ficonnection.
privatestaticbooleanwifiConnected=false;
//Whetherthereisamobileconnection.
privatestaticbooleanmobileConnected=false;
//Whetherthedisplayshouldberefreshed.
publicstaticbooleanrefreshDisplay=true;
publicstaticStringsPref=null;
...

//UsesAsyncTasktodownloadtheXMLfeedfromstackoverflow.com.
publicvoidloadPage(){

if((sPref.equals(ANY))&&(wifiConnected||mobileConnected)){
newDownloadXmlTask().execute(URL);
}
elseif((sPref.equals(WIFI))&&(wifiConnected)){
newDownloadXmlTask().execute(URL);
}else{
//showerror
}
}

动态下载xml

//ImplementationofAsyncTaskusedtodownloadXMLfeedfromstackoverflow.com.
privateclassDownloadXmlTaskextendsAsyncTask<String,Void,String>{
@Override
protectedStringdoInBackground(String...urls){
try{
returnloadXmlFromNetwork(urls[0]);
}catch(IOExceptione){
returngetResources().getString(R.string.connection_error);
}catch(XmlPullParserExceptione){
returngetResources().getString(R.string.xml_error);
}
}
@Override
protectedvoidonPostExecute(Stringresult){
setContentView(R.layout.main);
//DisplaystheHTMLstringintheUIviaaWebView
WebViewmyWebView=(WebView)findViewById(R.id.webview);
myWebView.loadData(result,"text/html",null);
}
}

加载xml

//UploadsXMLfromstackoverflow.com,parsesit,andcombinesitwith
//HTMLmarkup.ReturnsHTMLstring.
privateStringloadXmlFromNetwork(StringurlString)throwsXmlPullParserException,IOException{
InputStreamstream=null;
//Instantiatetheparser
StackOverflowXmlParserstackOverflowXmlParser=newStackOverflowXmlParser();
List<Entry>entries=null;
Stringtitle=null;
Stringurl=null;
Stringsummary=null;
CalendarrightNow=Calendar.getInstance();
DateFormatformatter=newSimpleDateFormat("MMMddh:mmaa");

//Checkswhethertheusersetthepreferencetoincludesummarytext
SharedPreferencessharedPrefs=PreferenceManager.getDefaultSharedPreferences(this);
booleanpref=sharedPrefs.getBoolean("summaryPref",false);

StringBuilderhtmlString=newStringBuilder();
htmlString.append("<h3>"+getResources().getString(R.string.page_title)+"</h3>");
htmlString.append("<em>"+getResources().getString(R.string.updated)+""+
formatter.format(rightNow.getTime())+"</em>");

try{
stream=downloadUrl(urlString);
entries=stackOverflowXmlParser.parse(stream);
//MakessurethattheInputStreamisclosedaftertheappis
//finishedusingit.
}finally{
if(stream!=null){
stream.close();
}
}

//StackOverflowXmlParserreturnsaList(called"entries")ofEntryobjects.
//EachEntryobjectrepresentsasinglepostintheXMLfeed.
//ThissectionprocessestheentrieslisttocombineeachentrywithHTMLmarkup.
//EachentryisdisplayedintheUIasalinkthatoptionallyincludes
//atextsummary.
for(Entryentry:entries){
htmlString.append("<p><ahref='");
htmlString.append(entry.link);
htmlString.append("'>"+entry.title+"</a></p>");
//Iftheusersetthepreferencethttp://oincludesummarytext,
//addsittothedisplay.
if(pref){
htmlString.append(entry.summary);
}
}
returnhtmlString.toString();
}
//GivenastringrepresentationofaURL,setsupaconnectionandgets
//aninputstream.
privateInputStreamdownloadUrl(StringurlString)throwsIOException{
URLurl=newURL(urlString);
HttpURLConnectionconn=(HttpURLConnection)url.openConnection();
conn.setReadTimeout(10000/*milliseconds*/);
conn.setConnectTimeout(15000/*milliseconds*/);
conn.setRequestMethod("GET");
conn.setDoInput(true);
//Startsthequery
conn.connect();
InputStreamstream=conn.getInputStream();
}

上面的片段代码为了帮助大家理解，这里还是老习惯，贴上项目的源代码，本来是有项目截图，运行效果图之类的图的，只是这篇文章太长了，再弄图片，就更占篇幅了，所以就只贴源码了，大家可以自己的运行起来看看，希望能从整体的架构和具体的代码细节上帮助到大家。点击打开下载链接