Web Services using Play!

A reasonably undocumented feature of Play is the ease in which Web Services can be integrated into your application. This quick blog will show you how easy it is to create a Play Web Application to do a currency conversion calculation, using Live currency rates between some popular currencies.If you have not already done so, download the latest version of Play from http://www.playframework.org.

Open your command prompt at the directory where you have unzipped and type.

play new currency

Follow the on-screen prompts to set up your new application.
Next start the server by typing

play run currency

Now, open the file currency/app/views/Application/index.html.
In this page we want to have two drop down lists with common currencies to select, and a value field. Change the code so that it looks like the following.

#{extends 'main.html' /}
#{set title:'Home' /}

<h1>Play! Currency Converter</h1>
<form action="@{Application.convert()}" method="POST">
    Currency From:
	<select name="from">
		<option value="USD">USD - US Dollar</option>
		<option value="GBP">GBP - UK Pound Sterling</option>
		<option value="EUR">EUR - Euro</option>
	</select><br />
    Currency To:
	<select name="to">
		<option value="USD">USD - US Dollar</option>
		<option value="GBP">GBP - UK Pound Sterling</option>
		<option value="EUR">EUR - Euro</option>
	</select><br />
	Amount: <input type="text" name="amount" /> <br />

	<input type="submit" name="conv" value="Convert" />
</form>

This code is fairly straightforward HTML. The only Play feature in the code is the form action which points to a Play action (which we will create next), using the @{Application.convert()} code.

Next, we need to open the app/controllers/Application.java.
We need to add the convert action to send our form data to. The file should look like this.

package controllers;

import play.mvc.*;
import play.libs.*;
import org.w3c.dom.Document;

public class Application extends Controller {
	
    public static void convert(String from, String to, Float amount) {
		
        String wsReq = "<?xml version=\"1.0\" encoding=\"utf-8\"?><soap12:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap12=\"http://www.w3.org/2003/05/soap-envelope\">" +
					  "<soap12:Body><ConversionRate xmlns=\"http://www.webserviceX.NET/\">" +
                      "<FromCurrency>"+from+"</FromCurrency>" +
                      "<ToCurrency>"+to+"</ToCurrency>"+
					  "</ConversionRate></soap12:Body></soap12:Envelope>";
					  
		Document doc = WS.url("http://www.webservicex.net/CurrencyConvertor.asmx").setHeader("Content-Type", "application/soap+xml").body(wsReq).post().getXml();
		String rate = doc.getElementsByTagName("ConversionRateResult").item(0).getTextContent();
		
		Float total = amount * Float.parseFloat(rate);
		render(from, to, amount, rate, total);
	}

    public static void index() {
        render();
    }
}

The main piece of code we are concerned about is the convert method. This method is called when the form is submitted (courtesy of the @{Application.convert()} code in the index.html page).
The method takes 3 parameters, which Play automatically maps from the HTTP parameters sent by the form, so we have the values present immediately when the method is created.

The first thing we do in the method (Play calls these methods actions, so we will do the same from now on), is to create the XML for the soap request. The XML is a reasonably simple SOAP request containing the envelope and body, and the currency symbols we want to convert from and to.

Next, is the WebService part of Play. To use web services in Play, we need to use the play.libs.WS class. Let’s take a closer look at the Web Service call.

Document doc = WS.url("http://www.webservicex.net/CurrencyConvertor.asmx").setHeader("Content-Type", "application/soap+xml").body(wsReq).post().getXml();

The first part of the request specifies the URL that we want to connect to. Here I am using a free sample webservice for live currencies. The second part adds a header to the request. For the request to work, the request needs to specify that the content is soap-xml, which is why the header needs to be added. The third part sets the body of the request to the SOAP xml we created at the start of the action, and the final part sends the SOAP request using the post method.
The final part (getXml()) returns the response as a Document object, ready for parsing.

The rest of the convert action simply gets the result from the returned XML, and calculates the total amount converted from the amount to convert multiplied by the exchange rate returned from the web service. All of the values (including the ones submitted by the form) are then passed through to the HTML page, so that they can be rendered, by calling the render method.

Finally, we need to output the results of the conversion. So let’s create a new file called app/views/Application/convert.html, and add the following code.

#{extends 'main.html' /}
#{set title:'Converted' /}

<h1>Total ${to} ${total}</h1>
Converted ${amount} ${from} to ${to} at an exchange rate of ${rate}

We can now try out our application. Go to http://localhost:9000 and you will see a page like this.

If we choose USD and GBP and set an amount, then click convert, we should see the results similar to the following.

To achieve this result, our code called an external web service to look up the Live exchange rate between these two currencies, and then used the results in our controller to perform the necessary calculations to display the results on the screen.

How cool is that! A currency conversion application, using real LIVE currency rates, written in less than 50 lines of code.

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