.net barcode reader camera Robust HTTP with HttpClient in Java

Create Quick Response Code in Java Robust HTTP with HttpClient

Robust HTTP with HttpClient
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To get started with HttpClient, we re going to look at using core classes to perform HTTP GET and POST method requests. We re going to concentrate on making network
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You ll find more about the Apache HttpClient here: http://hc.apache.org/httpclient-3.x/.
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Working with HTTP
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requests in a Thread separate from the UI, using a combination of the Apache ResponseHandler and Android Handler (for different but related purposes, as you ll see). The following listing shows our first example of using the HttpClient API.
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Listing 6.5 Apache HttpClient with Android Handler and Apache ResponseHandler
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. . . . private final Handler handler = new Handler() { public void handleMessage(Message msg) { progressDialog.dismiss(); String bundleResult = msg.getData().getString("RESPONSE"); Use Handler output.setText(bundleResult); to update UI } }; Create . . . onCreate omitted for brevity ResponseHandler private void performRequest() { for asynchronous final ResponseHandler<String> responseHandler = HTTP new ResponseHandler<String>() { public String handleResponse(HttpResponse response) { StatusLine status = response.getStatusLine(); HttpEntity entity = response.getEntity(); Get HTTP String result = null; response try { payload result = StringUtils.inputStreamToString(
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entity.getContent()); Message message = handler.obtainMessage(); Bundle bundle = new Bundle(); bundle.putString("RESPONSE", result); message.setData(bundle); handler.sendMessage(message); } catch (IOException e) { // log and or handle } return result; } }; this.progressDialog = ProgressDialog.show(this, "working . . .", Use separate Thread "performing HTTP request"); for HTTP call new Thread() { public void run() { try { DefaultHttpClient client = new DefaultHttpClient(); HttpGet httpMethod = new HttpGet( urlChooser.getSelectedItem().toString()); Create client.execute( HttpGet httpMethod, responseHandler); object } catch (ClientProtocolException e) { Execute // log and or handle HTTP with } catch (IOException e) { HttpClient // log and or handle
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} } }.start(); }
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The first thing we do in our initial HttpClient example is create a Handler that we can send messages to from other threads. This technique is the same one we ve used in previous examples; it allows background tasks to send Message objects to hook back into the main UI thread B. After we create an Android Handler, we create an Apache ResponseHandler C. This class can be used with HttpClient HTTP requests to pass in as a callback point. When an HTTP request that s fired by HttpClient completes, it calls the onResponse method if a ResponseHandler is used. When the response comes in, we get the payload using the HttpEntity the API returns D. This in effect allows the HTTP call to be made in an asynchronous manner we don t have to block and wait the entire time between when the request is fired and when it completes. The relationship of the request, response, Handler, ResponseHandler, and separate threads is diagrammed in figure 6.3. Now that you ve seen HttpClient at work and understand the basic approach, the next thing we ll do is encapsulate a few of the details into a convenient helper class so that we can call it over and over without having to repeat a lot of the setup.
Creating an HTTP and HTTPS helper
The next Activity in our NetworkExplorer application, which is shown in listing 6.6, is a lot more straightforward and Android-focused than our other HTTP-related classes up to this point. We ve used the helper class we mentioned previously, which
Non UI Thread - network request
Apache HttpClient execute(method, responseHandler)
HTTP request
HTTP server Apache ResponseHandler handleResponse(httpResponse) HTTP response
Android Handler sendMessage(message) onMessage(message)
UI Thread - UI updates
Figure 6.3 The relationship between HttpClient, ResponseHandler, and Android Handler
Working with HTTP
hides some of the complexity. We ll examine the helper class itself after we look at this first class that uses it.
Listing 6.6 Using Apache HttpClient via a custom HttpRequestHelper
public class ApacheHTTPViaHelper extends Activity { . . . other member variables omitted for brevity private final Handler handler = new Handler() { public void handleMessage(Message msg) { progressDialog.dismiss(); String bundleResult = msg.getData().getString("RESPONSE"); output.setText(bundleResult); } }; @Override public void onCreate(final Bundle icicle) { super.onCreate(icicle); . . . view inflation and setup omitted for brevity this.button.setOnClickListener(new OnClickListener() { public void onClick(final View v) { Call local output.setText(""); performRequest performRequest( urlChooser.getSelectedItem().toString()); } }); }; . . . onPause omitted for brevity private void performRequest(String url) { final ResponseHandler<String> responseHandler = HTTPRequestHelper.getResponseHandlerInstance( this.handler);
from RequestHelper this.progressDialog = ProgressDialog.show(this, "working . . .", "performing HTTP request"); new Thread() { Instantiate public void run() { RequestHelper with HTTPRequestHelper helper = new ResponseHandler HTTPRequestHelper(responseHandler); helper.performGet(url, null, null, null); } }.start();
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