Android Xml Parsing导致App Crash引起：android.os.NetworkOnMainThreadException

Question

我正在学习在Android中解析Xml ...我只是将我的Xml文件放在服务器中我想在Listview中显示标题标签名称但是当我试图解析我的应用程序时崩溃并且在logcat中它说引起：android.os.NetworkOnMainThreadException

这是Xml代码

<rss version="2.0">
<channel>
<title>Website Names</title>
<item>
<title>Google</title>
<link>www.google.com</link>
</item>
<item>
<title>Yahoo</title>
<link>www.yahoo.com</link>
</item>

Xml Parser：

public class XMLParser {

    // constructor
    public XMLParser() {

    }

    /**
     * Getting XML from URL making HTTP request
     * @param url string
     * */
    public String getXmlFromUrl(String urlString) {
        String xml = null;

        URL url;
        HttpURLConnection urlConnection = null;

        try {
            url = new URL(urlString);

            urlConnection = (HttpURLConnection) url.openConnection();

            InputStream in = urlConnection.getInputStream();

            InputStreamReader isw = new InputStreamReader(in);

            BufferedReader br = new BufferedReader(isw);
            StringBuilder sb = new StringBuilder();
            String line;
            while ((line = br.readLine()) != null) {
                sb.append(line+"\n");
            }
            br.close();

            xml = sb.toString();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }


        // return XML
        return xml;
    }

    /**
     * Getting XML DOM element
     * @param XML string
     * */
    public Document getDomElement(String xml){
        Document doc = null;
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        try {

            DocumentBuilder db = dbf.newDocumentBuilder();

            InputSource is = new InputSource();
            is.setCharacterStream(new StringReader(xml));
            doc = db.parse(is);

        } catch (ParserConfigurationException e) {
            Log.e("Error: ", e.getMessage());
            return null;
        } catch (SAXException e) {
            Log.e("Error: ", e.getMessage());
            return null;
        } catch (IOException e) {
            Log.e("Error: ", e.getMessage());
            return null;
        }

        return doc;
    }

    /** Getting node value
     * @param elem element
     */
    public final String getElementValue( Node elem ) {
        Node child;
        if( elem != null){
            if (elem.hasChildNodes()){
                for( child = elem.getFirstChild(); child != null; child = child.getNextSibling() ){
                    if( child.getNodeType() == Node.TEXT_NODE  ){
                        return child.getNodeValue();
                    }
                }
            }
        }
        return "";
    }

    /**
     * Getting node value
     * @param Element node
     * @param key string
     * */
    public String getValue(Element item, String str) {
        NodeList n = item.getElementsByTagName(str);
        return this.getElementValue(n.item(0));
    }
}

MainActivity：

public class MainActivity extends ListActivity {
    // All static variables
    static final String URL = "http://server.com/resource/website";
    // XML node keys
    static final String KEY_ITEM = "item"; // parent node
    static final String KEY_TITLE = "title";
    static final String KEY_LINK = "link";



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

        XMLParser parser = new XMLParser();
        String xml = parser.getXmlFromUrl(URL); // getting XML
        Document doc = parser.getDomElement(xml); // getting DOM element


        NodeList nl = doc.getElementsByTagName(KEY_ITEM);
        // looping through all item nodes <item>
        for (int i = 0; i < nl.getLength(); i++) {
            // creating new HashMap
            HashMap<String, String> map = new HashMap<String, String>();
            Element e = (Element) nl.item(i);
            // adding each child node to HashMap key => value
            map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
            map.put(KEY_LINK, parser.getValue(e, KEY_LINK));
            // adding HashList to ArrayList
            menuItems.add(map);
        }

        ListAdapter adapter = new SimpleAdapter(this, menuItems,
                R.layout.list_item,
                new String[] { KEY_TITLE }, new int[] {
                R.id.title });

        setListAdapter(adapter);


    }

logcat的：

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.a.ro/com.example.a.ro.MainActivity}: android.os.NetworkOnMainThreadException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2436)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2498)
            at android.app.ActivityThread.access$900(ActivityThread.java:179)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1324)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:146)
            at android.app.ActivityThread.main(ActivityThread.java:5641)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1288)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1104)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: android.os.NetworkOnMainThreadException
            at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1166)
            at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
            at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
            at java.net.InetAddress.getAllByName(InetAddress.java:214)
            at com.android.okhttp.internal.Dns$1.getAllByName(Dns.java:28)
            at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:216)
            at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:122)
            at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:292)
            at com.android.okhttp.internal.http.HttpEngine.sendSocketRequest(HttpEngine.java:255)
            at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:206)
            at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:345)
            at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:296)
            at com.android.okhttp.internal.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:179)
            at com.example.a.ro.XMLParser.getXmlFromUrl(XMLParser.java:53)
            at com.example.a.ro.MainActivity.onCreate(MainActivity.java:36)