Tutorial

Michael Pallotta

We received a lot of question to add a how-to or tutorial to this website. This tutorial will show you how to consume a web service in different programming environments.

The Web service

First of all we need a web service to use. We have set up a a web service called add. This service will take two integers as input and return the sum.

Service Implementation - HTTP GET

HTTP GET is the easiest way to consume a web service: call a URL, add some parameters and parse the output. In this case the service end point is at https://free-web-services.com/add and the parameters must be named 'a' and 'b'. You can easily check the output by clicking on the next URL: https://free-web-services.com/add?a=5&b=7 .

Sample code in PHP:

<?php

$a = 4;
$b = 9;

$url = 'http://free-web-services.com/add?a=' . urlencode($a) . '&b=' . urlencode($b);

$output = file_get_contents($url);

echo $output;

?>

The output will be:

13

Service Implementation - JSON (HTTP POST)

The same service end point can be used to POST a JSON object. The result will be a new JSON object with two properties: sum (the actual sum) and time (the time needed to calculate the sum).

Sample code in PHP:

<?php

$obj = new StdClass();
$obj->a = 4;
$obj->b = 9;

//--- Use curl to do the HTTP-POST transport
$ch = curl_init();

curl_setopt($ch,CURLOPT_URL,            'http://free-web-services.com/add');
curl_setopt($ch,CURLOPT_POST,           true);
curl_setopt($ch,CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch,CURLOPT_POSTFIELDS,     json_encode($obj));

//--- Execute
$result = curl_exec($ch);

//--- Get the HTTP result
$httpStatus = curl_getinfo($ch, CURLINFO_HTTP_CODE);

//--- Close curl handle
curl_close($ch);

if ($httpStatus == 200) {
  //--- Success
  $resultObj = json_decode($result);
  echo "Sum = " . $resultObj->sum . "\n";
  echo "Time = " . $resultObj->time . "\n";
} else {
  //--- Error
  echo "Server returned error " . $httpStatus . ".\n";
} 

?>

The output will be:

Sum = 13

Time = 0.002

Service Implementation - SOAP

Soap is more complex. But when you use a development enviroment that offers out-of-the-box soap clients it is actually very simple. The "add" service is described in https://free-web-services.com/add.wsdl. This is an XML document describing the transport methods, input and output messages and available operations. In this case only the "add" method is available.

Create a new command line project in C# and add a service reference:
Then create a small program that uses this service reference:

namespace ExampleProgram1
{
    class Program
    {
        static void Main(string[] args)
        {
            var client = new ServiceReference1.addSoapClient();
            double time;
            int sum = client.add(13, 17, out time);

            System.Console.Out.WriteLine("sum = " + sum);
            System.Console.Out.WriteLine("time = " + time);
        }
    }
}

Or a similar program in PHP:

<?php

$client = new SoapClient('http://free-web-services.com/add.wsdl');

try {
  $response = $client->add(array("a" => 13, "b" => 17));
  echo "sum = " . $response->sum . "\n";
  echo "time = " . $response->time . "\n";
} catch (SoapFault $fault) {
  echo "Error: " . $fault->faultcode . ": " . $fault->getMessage() . "\n";
}

In both programs the output should be:

sum = 30

time = 0.0002

---

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