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<h1>RESTful Web Services Support</h1>

<p>REST is providing access to resources through the two methods GET and
POST. The REST Web services are reduced subset of the usual Web Service
stack, and the Axis2 REST implementation assumes following properties.</p>
<ol>
  <li>REST Web services are Synchronous, and Request Response in nature.</li>
  <li>When the REST Web Services are accessed via GET, the service and the
    operations are identified based on the URL and the parameters are assumed
    as parameters of the Web Service. In this case the GET based REST web
    services supports only simple types as arguments.</li>
  <li>POST based web services do not need a SOAP Envelope or a SOAP Body.
    REST Web Services do not have Headers and the payload is directly
  sent.</li>
</ol>

<p>Axis2 can be configured as a REST Container and can be used to send and
receive RESTful web services requests and responses. The REST Web Services
can be access in two ways, i.e. using HTTP GET and POST.</p>

<h2>Doing REST web services with HTTP POST</h2>

<p>REST's default HTTP interface is POST. It can be enabled in the
Server/Client side by adding the following line to the axis2.xml file.</p>
<font color="blue">&lt; parameter name="enableREST" locked="false" &gt; true
&lt;/parameter&gt; </font>

<p>But it acts both as a REST endpoint as well as a SOAP endpoint. When a
Message is received, if the content type is text/xml and if the SOAP Action
Headers are missing, then the Message is treated as a RESTful Message. Else
it is treated as a usual SOAP Message.</p>

<p>On sending a message out, the fact that the message is RESTful or not, can
be decided from the client API or by deployment descriptor of the client.</p>
<ol>
  <li>By adding an entry in the client repositories axis2.xml file.</li>
  <li>Setting as a property in client API e.g. <source>
    <pre>...
Options options = new Options();
options.setProperty(Constants.Configuration.ENABLE_REST, Constants.VALUE_TRUE);
...</pre>
    </source></li>
</ol>

<h3>Sample REST - HTTP POST Client</h3>

<p>There is an example named, userguide.clients.RESTClient.java which
demonstrates the usage of the above, using the "echo"operation of the
<source></p>
<pre>userguide.example1.MyService </pre>

<p>of the samples. And the class source will be as follows:</p>

<p><source></p>
<pre>public class RESTClient {

    private static String toEpr = "http://localhost:8080/axis2/services/MyService";

    public static void main(String[] args) throws AxisFault {

        Options options = new Options();
        options.setTo(new EndpointReference(toEpr));
        options.setListenerTransportProtocol(Constants.TRANSPORT_HTTP);
        options.setUseSeparateListener(false);
        options.setProperty(Constants.Configuration.ENABLE_REST, Constants.VALUE_TRUE);

        Call call = new Call();
        call.setClientOptions(options);
        
        OMElement result = call.invokeBlocking("echo", getPayload());

        try {
            XMLStreamWriter writer = XMLOutputFactory.newInstance()
                   .createXMLStreamWriter(System.out);
            result.serialize(writer);
            writer.flush();
        } catch (XMLStreamException e) {
            e.printStackTrace();
        } catch (FactoryConfigurationError e) {
            e.printStackTrace();
        }
    }

    private static OMElement getPayload() {
        OMFactory fac = OMAbstractFactory.getOMFactory();
        OMNamespace omNs = fac.createOMNamespace(
                "http://example1.org/example1", "example1");
        OMElement method = fac.createOMElement("echo", omNs);
        OMElement value = fac.createOMElement("Text", omNs);
        value.addChild(fac.createText(value, "Axis2 Echo String "));
        method.addChild(value);

        return method;
    }
}</pre>
</source>
<h2>Access a REST Web Service Via HTTP GET</h2>

<p>Axis2 lets the user to access Web Services that has simple type parameters
via the HTTP GET. For example the following URL requests the Version Service
via HTTP GET. But the web service arrives via GET assumes REST . Other
parameters are converted in to XML and put them in to the SOAP Body.</p>
<source><pre>http://127.0.0.1:8080/axis2/services/version/getVersion</pre>
</source>
<p>Result can be shown in the browser as follows.</p>
<img src="images/userguide/http-get-ws.png">

<p>For an example, the following request, <source></p>
<pre>http://127.0.0.1:8080/axis2/services/version/getVersion</pre>
</source>will be converted to the following SOAP Message for processing by
Axis2.<source>
<pre> 
   &lt;soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/"&gt;
      &lt;soapenv:Body&gt;   
          &lt;axis2:getVersion xmlns:axis2="http://ws.apache.org/goGetWithREST" /&gt;
      &lt;/soapenv:Body&gt;
   &lt;/soapenv:Envelope&gt;
    </pre>
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