Developing Weather Application using Dojo Mobile

http://www.technicaladvices.com/2012/05/31/developing-weather-application-using-dojo-mobile

Abstract

Dojo mobile (dojox/mobile) is one of the most powerful JavaScript frameworks that enable you to build cross mobiles web applications. It does not only contain mobile components but also it mimics the interface of the different mobile devices. Adding to this it responds to the mobile orientations. In this article, I will illustrate how to use the framework for building a weather application on the iPhone mobile.

Application Story

The application story is simple. In the weather mobile application, the user can get the current weather forecasting of a specific location. The user can do this by selecting one city from a list of available cities in the drop down and then click the “Get Information” button to get the weather information as shown in the screenshot below.

Building the weather application

In order to create the weather forecasting page, we need to know the main parts of the Dojo mobile page:

• The Doc Type and META tags.
• The mobile script and style includes.
• The application pages.

The Doc Type and META Tags

The Doc type that is recommended to be used is the HTML5 doctype as shown below:

For the META tags, it is important to use the "viewport" META tag to setup cross-device layout as shown below:

 name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,minimum-scale=1,user-scalable=no"/>

The other important META tag is an iPhone specific one which is the “apple-mobile-web-app-capable”. It is recommend to be set to “yes” to make the web application runs in full-screen mode as shown below:

 name="apple-mobile-web-app-capable" content="yes"/>

The script and style includes

Now, we come to the script and style includes. I’m using Dojo 1.7.1 for this application; in order to include the script and the style files; this can be done as shown below:

 rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.7.1/dojox/mobile/themes/iphone/iphone.css" rel="stylesheet">

 src="http://ajax.googleapis.com/ajax/libs/dojo/1.7.1/dojo/dojo.js" data-dojo-config="async: true">

I only included the iPhone CSS file, and the dojo.js file which is loaded asynchronously for including only the resources we need to keep the application optimized.
After including the script and the style, we need to use the require statements for including the Dojo modules. I use the new Asynchronous Modules (AMD) convention for making asynchronous loading of the modules as shown below:

require(["dojox/mobile/parser", "dojo/_base/xhr", "dojox/mobile", "dojox/mobile/deviceTheme",
         "dojox/mobile/TextBox", "dojox/mobile/Button", "dojox/mobile/compat",
	 "dijit/form/DataList", "dojox/mobile/ComboBox",
         "dojo/domReady!"], function(parser) {

		//...
		parser.parse();
	});

The following modules are loaded:

• The Dojo mobile parser "dojox/mobile/parser" for converting the HTML elements to Dojo mobile components.
• The Dojo XHR module "dojo/_base/xhr" for allowing performing Ajax requests.
• The Dojo mobile device theme "dojox/mobile/deviceTheme", for allowing detecting the mobile type and loading the proper theme correctly.
• "dojox/mobile/TextBox", "dojox/mobile/Button", "dijit/form/DataList", "dojox/mobile/ComboBox", for loading the mentioned components.
• The "dojox/mobile/compat" module is required for allowing having cross mobiles CSS3 animations.
• "dojo/domReady!" module is a replacement for the old dojo.ready API. The exclamation mark is required to tell Dojo not to execute the callback until the DOM is ready.

Finally in the callback, I’m using only the first parameter which is the parser object. The parser.parse statement is called for allowing the Dojo mobile parser to convert the HTML elements to Dojo mobile components.

The Application Pages

In our weather application, we have mainly two pages; the weather forecasting page and the about page. In order to make the pages scroll to the left and the right while navigation, we need to use the Dojo mobile views. The Dojo mobile views are normal HTML elements with the dojo type "dojox.mobile.View". To define the two views, we can do this as shown below:

 id="weather" dojoType="dojox.mobile.View" selected="true">
	...

id="about" dojoType="dojox.mobile.View"> ... The main view should be marked as selected by setting the selected attribute to "true".
In the weather forecasting page, there are three main elements:

• Heading element.
• Combo Box of the available cities.
• The “Get Information” button.

In order to create the heading element, you can mark an HTML element h1 with the “dojox.mobile.Heading” dojo type as follows:

 dojoType="dojox.mobile.Heading">Weather
	 dojoType="dojox.mobile.ToolBarButton" moveTo="about">About

I included a toolbar button for moving to the other view. The moveTo attribute can have the id of the view to switch to, in our case it is the about view id.
In order to create the combo box element, we need to use two tags, one for the data which is the dijit.form.DataList, and the other for the widget itself which is the dojox.mobile.ComboBox as follows:

 data-dojo-type="dijit.form.DataList" data-dojo-props="id:'locationList'" >
   selected>Cairo, Egypt
  Stockholm, Sweden
  Vienna, Austria
  Madrid, Spain
  Paris, France
  New York, USA
  Lima, Peru


 id="location" class="ninety" type="text" data-dojo-type="dojox.mobile.ComboBox" data-dojo-props="list:'locationList'" />

The “location” combo box is referring to the “locationList” using the list attribute.
The “Get Information” button calls the getWeatherInformation function to get the weather information as follows:

 class="mblBlueButton full" dojoType="dojox.mobile.Button" onClick="getWeatherInformation();">Get Information

The getWeatherInformation JavaScript function is calling a proxy Java Servlet that interacts with the Yahoo weather service API using dojo xhrGet.

function getWeatherInformation() {
	var selectedCode = cityMap[dijit.byId("location").value];

	dojo.xhrGet({
		url: "/mobileSamples/weatherProxyServlet?w=" + selectedCode,
		handleAs: "text",
		load: function(data) {
			document.getElementById("weatherResult").innerHTML = data;
		}
	});
}

The location value is read from the “location” combo box and the code of the location is retrieved from a custom JavaScript Map that I created for mapping the WOEID (Where on earth identification) to the locations.
When the HTML response is returned from the server, it is displayed directly in the "weatherResult" span.
Finally in the weather forecasting view, I embed the combo box and the button in the "dojox.mobile.RoundRect" div as follows:

 dojoType="dojox.mobile.RoundRect" shadow="true">
	 for="txtLocation">Select location 


	 data-dojo-type="dijit.form.DataList" data-dojo-props="id:'locationList'" >
	   selected>Cairo, Egypt
	  Stockholm, Sweden
	  Vienna, Austria
	  Madrid, Spain
	  Paris, France
	  New York, USA
	  Lima, Peru
	

	 id="location" class="ninety" type="text" data-dojo-type="dojox.mobile.ComboBox" data-dojo-props="list:'locationList'" />


	 class="mblBlueButton full" dojoType="dojox.mobile.Button" onClick="getWeatherInformation();">Get Information


	 id="weatherResult"/>

The other “about” view element is a simple one that contains description for the sample as follows:

 id="about" dojoType="dojox.mobile.View">
	 dojoType="dojox.mobile.Heading" back="back" moveTo="weather">About
	 dojoType="dojox.mobile.RoundRect">This sample is developed by TechnicalAdvices.COM. It is powered by Dojo Mobile.

It contains a heading that includes a back button using the back attribute. The back attribute should be set to id of the view element that the application navigates to when the back button is clicked.
The next code listing shows the complete code of the weather forecasting page:

	 name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,minimum-scale=1,user-scalable=no"/>
	 name="apple-mobile-web-app-capable" content="yes"/>
	 

	 rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/dojo/1.7.1/dojox/mobile/themes/iphone/iphone.css" rel="stylesheet">
	 src="http://ajax.googleapis.com/ajax/libs/dojo/1.7.1/dojo/dojo.js" data-dojo-config="async: true">

	 type="text/javascript">
		var cityMap = {};

		require(["dojox/mobile/parser", "dojo/_base/xhr", "dojox/mobile", "dojox/mobile/deviceTheme",
		         "dojox/mobile/TextBox", "dojox/mobile/Button", "dojox/mobile/compat",
		         "dijit/form/DataList", "dojox/mobile/ComboBox",
		         "dojo/domReady!"], function(parser) {

					// initialize WOIDs ...
					cityMap["Cairo, Egypt"] = "1521894";
					cityMap["Stockholm, Sweden"] = "906057";
					cityMap["Vienna, Austria"] = "551801"
					cityMap["Madrid, Spain"] = "766273";
					cityMap["Paris, France"] = "615702";
					cityMap["New York, USA"] = "2459115";
					cityMap["Lima, Peru"] = "418440";

					parser.parse();
				});

		function getWeatherInformation() {
			var selectedCode = cityMap[dijit.byId("location").value];

			dojo.xhrGet({
			    url: "/mobileSamples/weatherProxyServlet?w=" + selectedCode,
			    handleAs: "text",
			    load: function(data) {
			    	document.getElementById("weatherResult").innerHTML = data;
			    }
			});
		}
	 

	



	 id="weather" dojoType="dojox.mobile.View" selected="true">
		 dojoType="dojox.mobile.Heading">Weather
			 dojoType="dojox.mobile.ToolBarButton" moveTo="about">About
		

		 dojoType="dojox.mobile.RoundRect" shadow="true">
			 for="txtLocation">Select location 


			 data-dojo-type="dijit.form.DataList" data-dojo-props="id:'locationList'" >
			   selected>Cairo, Egypt
			  Stockholm, Sweden
			  Vienna, Austria
			  Madrid, Spain
			  Paris, France
			  New York, USA
			  Lima, Peru
			

			 id="location" class="ninety" type="text" data-dojo-type="dojox.mobile.ComboBox" data-dojo-props="list:'locationList'" />


			 class="mblBlueButton full" dojoType="dojox.mobile.Button" onClick="getWeatherInformation();">Get Information


			 id="weatherResult"/>
		
	

	 id="about" dojoType="dojox.mobile.View">
		 dojoType="dojox.mobile.Heading" back="back" moveTo="weather">About
		 dojoType="dojox.mobile.RoundRect">This sample is developed by TechnicalAdvices.COM. It is powered by Dojo Mobile.
						

The Backend Java Servlet

Finally, the backend Java Servlet reads the WOEID parameter and opens a URL connection to the yahoo API weather forecasting URL for getting the weather forecasting of the location as shown in the code listing below.

package servlets;

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.HttpURLConnection;
import java.net.ProtocolException;
import java.net.URL;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sun.syndication.feed.synd.SyndEntry;
import com.sun.syndication.feed.synd.SyndFeed;
import com.sun.syndication.io.SyndFeedInput;

/**
 * WeatherProxyServlet is a proxy servlet that wraps Yahoo weather REST service.
 * @author hazems
 *
 */
public class WeatherProxyServlet extends HttpServlet {
	private static final long serialVersionUID = 8732370454506907957L;

	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {

		String WOEID = request.getParameter("w");
		HttpURLConnection connection = null;

		response.setContentType("text/html");

		PrintWriter writer = null;

		try {
			URL url = new URL("http://weather.yahooapis.com/forecastrss?u=c&w=" + WOEID);

			connection = createHTTPConnection(url);

			String output = getHTTPOutputResponse(connection);

			SyndFeedInput input = new SyndFeedInput();
			SyndFeed feed = input.build(new InputStreamReader(new ByteArrayInputStream(output.getBytes("UTF-8"))));  		

		    if (feed.getEntries() != null && feed.getEntries().size() > 0) {
	            SyndEntry entry = ((SyndEntry) feed.getEntries().get(0));

	            String title = entry.getTitle();
	            String description = entry.getDescription().getValue();

	            if (description.contains("Invalid")) {
	            	throw new Exception(description);
	            }

	    		writer = response.getWriter();
	            writer.print(title + "
" + description);
	        }
		} catch (Exception exception) {
			throw new ServletException(exception.getMessage());
		} finally {
			if (connection != null) {
				connection.disconnect();
			}

			if (writer != null) {
				writer.flush();
	        	writer.close();
			}
		}
	}

	private static HttpURLConnection createHTTPConnection(URL url) throws IOException, ProtocolException {
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();

		conn.setDoOutput(true);
		conn.setDoInput(true);
		conn.setRequestMethod("GET");
		conn.setRequestProperty("Accept", "text/html");
		conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");

		return conn;
	}

	private static String getHTTPOutputResponse(HttpURLConnection conn) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader((conn.getInputStream())));

		String httpOutputResponse = "";
		String outputLine;

		while ((outputLine = br.readLine()) != null) {
			httpOutputResponse += outputLine;
		}

		return httpOutputResponse;
	}
}

You can try the application from your iPhone by going to the following URL:
http://www.mashups4jsf.com/mobileSamples/weather.jsp
You can download the complete Eclipse project from the following URL:
https://www.ibm.com/developerworks/mydeveloperworks/blogs/hazem/resource/29052012/mobileSamples.zip

Conclusion

In this article, you learned how to build a mobile application using the Dojo mobile APIs. You know how to use the framework views, headings, and components for building the weather forecasting application.