BlackBerry read json string from an URL

Question

I tried to read a json string loading from an URL, but I could not find complete code sample. Can any one provide or point me to a complete client code. I'm newer to BB development.

this is what I have done but still can't get it work please help me.

Thanks!

Answer 1

To read and parse data from an URL you need to implement two routines. First one of them will handle reading data from the specified URL over HTTP connection, and the second one will parse the data.

Check the following application HttpUrlReaderDemoApp, which will first read the data from specified URL and then parse the retrieved data.

• URL used to retrieve data: http://codeincloud.tk/json_android_example.php
• Sample data format: {"name":"Froyo", "version":"Android 2.2"}

Classes:

• HttpUrlReaderDemoApp - UiApplication instance
• HttpResponseListener - Interface used to notify other classes about HTTP request status
• HttpUrlReader - Reads the data from given url
• AppMainScreen - MainScreen instance
• DataParser - Parse data
• DataModel - Data definition

Screenshots:

• Request for data

  

• When data retrieved successfully

  

• Parsed data

  

Implementation:

HttpUrlReaderDemoApp

public class HttpUrlReaderDemoApp extends UiApplication {
    public static void main(String[] args) {
        HttpUrlReaderDemoApp theApp = new HttpUrlReaderDemoApp();
        theApp.enterEventDispatcher();
    }

    public HttpUrlReaderDemoApp() {
        pushScreen(new AppMainScreen("HTTP Url Reader Demo Application"));
    }
}

HttpResponseListener

public interface HttpResponseListener {
    public void onHttpResponseFail(String message, String url);

    public void onHttpResponseSuccess(byte bytes[], String url);
}

HttpUrlReader

public class HttpUrlReader implements Runnable {
    private String url;
    private HttpResponseListener listener;

    public HttpUrlReader(String url, HttpResponseListener listener) {
        this.url = url;
        this.listener = listener;
    }

    private String getConncetionDependentUrlSuffix() {
        // Not implemented
        return "";
    }

    private void notifySuccess(byte bytes[], String url) {
        if (listener != null) {
            listener.onHttpResponseSuccess(bytes, url);
        }
    }

    private void notifyFailure(String message, String url) {
        if (listener != null) {
            listener.onHttpResponseFail(message, url);
        }
    }

    private boolean isValidUrl(String url) {
        return (url != null && url.length() > 0);
    }

    public void run() {
        if (!isValidUrl(url) || listener == null) {
            String message = "Invalid parameters.";
            message += !isValidUrl(url) ? " Invalid url." : "";
            message += (listener == null) ? " Invalid HttpResponseListerner instance."
                    : "";
            notifyFailure(message, url);
            return;
        }

        // update URL depending on connection type
        url += DeviceInfo.isSimulator() ? ";deviceside=true"
                : getConncetionDependentUrlSuffix();

        // Open the connection and retrieve the data
        try {
            HttpConnection httpConn = (HttpConnection) Connector.open(url);
            int status = httpConn.getResponseCode();
            if (status == HttpConnection.HTTP_OK) {
                InputStream input = httpConn.openInputStream();
                byte[] bytes = IOUtilities.streamToBytes(input);
                input.close();
                notifySuccess(bytes, url);
            } else {
                notifyFailure("Failed to retrieve data, HTTP response code: "
                        + status, url);
                return;
            }
            httpConn.close();
        } catch (Exception e) {
            notifyFailure("Failed to retrieve data, Exception: ", e.toString());
            return;
        }
    }
}

AppMainScreen

public class AppMainScreen extends MainScreen implements HttpResponseListener {
    private final String URL = "http://codeincloud.tk/json_android_example.php";

    public AppMainScreen(String title) {
        setTitle(title);
    }

    private MenuItem miReadData = new MenuItem("Read data", 0, 0) {
        public void run() {
            requestData();
        }
    };

    protected void makeMenu(Menu menu, int instance) {
        menu.add(miReadData);
        super.makeMenu(menu, instance);
    }

    public void close() {
        super.close();
    }

    public void showDialog(final String message) {
        UiApplication.getUiApplication().invokeLater(new Runnable() {
            public void run() {
                Dialog.alert(message);
            }
        });
    }

    private void requestData() {
        Thread urlReader = new Thread(new HttpUrlReader(URL, this));
        urlReader.start();
        showDialog("Request for data from\n \"" + URL + "\"\n started.");
    }

    public void onHttpResponseFail(String message, String url) {
        showDialog("Failure Mesage:\n" + message + "\n\nUrl:\n" + url);
    }

    public void onHttpResponseSuccess(byte bytes[], String url) {
        showDialog("Data retrived from:\n" + url + "\n\nData:\n"
                + new String(bytes));

        // now parse response
        DataModel dataModel = DataParser.getData(bytes);
        if (dataModel == null) {
            showDialog("Failed to parse data: " + new String(bytes));
        } else {
            showDialog("Parsed Data:\nName: " + dataModel.getName()
                    + "\nVersion: " + dataModel.getVersion());
        }
    }
}

DataParser

public class DataParser {
    private static final String NAME = "name";
    private static final String VERSION = "version";

    public static DataModel getData(byte data[]) {
        String rawData = new String(data);
        DataModel dataModel = new DataModel();

        try {
            JSONObject jsonObj = new JSONObject(rawData);
            if (jsonObj.has(NAME)) {
                dataModel.setName(jsonObj.getString(NAME));
            }
            if (jsonObj.has(VERSION)) {
                dataModel.setVersion(jsonObj.getString(VERSION));
            }
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }

        return dataModel;
    }
}

DataModel

public class DataModel {
    private String name;
    private String version;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getVersion() {
        return version;
    }

    public void setVersion(String model) {
        this.version = model;
    }
}