Android连接网络

一、所需权限：

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

二、关键方法

public class HttpExampleActivity extends Activity {private static final String DEBUG_TAG = "HttpExample";private EditText urlText;private TextView textView;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);urlText = (EditText) findViewById(R.id.myUrl);textView = (TextView) findViewById(R.id.myText);}// When user clicks button, calls AsyncTask.// Before attempting to fetch the URL, makes sure that there is a network connection.public void myClickHandler(View view) {// Gets the URL from the UI's text field.String stringUrl = urlText.getText().toString();ConnectivityManager connMgr = (ConnectivityManager)        getSystemService(Context.CONNECTIVITY_SERVICE);NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();if (networkInfo != null && networkInfo.isConnected()) {new DownloadWebpageText().execute(stringUrl);} else {textView.setText("No network connection available.");}}// Uses AsyncTask to create a task away from the main UI thread. This task takes a// URL string and uses it to create an HttpUrlConnection. Once the connection// has been established, the AsyncTask downloads the contents of the webpage as// an InputStream. Finally, the InputStream is converted into a string, which is// displayed in the UI by the AsyncTask's onPostExecute method.private class DownloadWebpageText extends AsyncTask {@Overrideprotected String doInBackground(String... urls) {// params comes from the execute() call: params[0] is the url.try {return downloadUrl(urls[0]);} catch (IOException e) {return "Unable to retrieve web page. URL may be invalid.";}}// onPostExecute displays the results of the AsyncTask.@Overrideprotected void onPostExecute(String result) {textView.setText(result);}// Given a URL, establishes an HttpUrlConnection and retrieves// the web page content as a InputStream, which it returns as// a string.private String downloadUrl(String myurl) throws IOException {InputStream is = null;// Only display the first 500 characters of the retrieved// web page content.int len = 500;try {URL url = new URL(myurl);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setReadTimeout(10000 /* milliseconds */);conn.setConnectTimeout(15000 /* milliseconds */);conn.setRequestMethod("GET");conn.setDoInput(true);// Starts the queryconn.connect();int response = conn.getResponseCode();Log.d(DEBUG_TAG, "The response is: " + response);is = conn.getInputStream();// Convert the InputStream into a stringString contentAsString = readIt(is, len);return contentAsString;// Makes sure that the InputStream is closed after the app is// finished using it.} finally {if (is != null) {is.close();}}}// Reads an InputStream and converts it to a String.public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {Reader reader = null;reader = new InputStreamReader(stream, "UTF-8");char[] buffer = new char[len];reader.read(buffer);return new String(buffer);}}...
}

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