As is well known, Web Services can be accessed via the
HTTP-based protocol. The great object—XMLHttpRequest,
therefore, may be used directly to call Web Services. According to the features
of XMLHttpRequest and Web Services and what the client side needs, the whole
process can be divided into three detailed steps.
·
Send the HTTP requests to Web Services via XMLHttpRequest and get
the corresponding HTTP responses.
·
Resolve the XML data returned from the server and pick out the
needed data.
·
Render the acquired data via the client-side JavaScript.
No doubt that the difficulty lies in Step 2—resolving XML in the client side. In this
aspect, different browsers have offered different solutions. In Microsoft
Internet Explorer, we can achieve our goal by resorting to the ActiveX control—XMLDOM. As for other browsers, such as Mozilla's
FireFox, Opera, etc., the third-party script libraries are often borrowed in
order to resolve XML data. For example, Google's google
ajaxslt can resolve XML and convert XSLT.
Joyfully, to obtain the required data from the XML object
returned via Web Services does not need to resolve XML completely. Thus, besides
the HTTP protocol scheme, we can use SOAP (Simple Object Access Protocol) to
call a Web Service, such as the SOAP-based JavaScript library—soapclient.js. This library can be
downloaded from www.guru4.net and the
accompanied source codes in this article also provide one. Figure 1 gives us
the general depiction of this small framework.
Figure 1: The mechanism of calling web services
provided by soapclient.js
This script is so direct and simple to use that we only give
a corresponding sample.
First, define the Web service as usual.
Listing 1
[WebMethod]
Public string HelloWorld()
{
Return "Hello World!";
}Next, write the client-side JavaScript to call the Web
service.
Listing 2
function HelloWorld()
{
var pl =new SOAPClientParameters();
SOAPClient.invoke(url, "Hello World", pl, true, HelloWorld_callback);
}
function HelloWorld_callback(r)
{
alert(r);
}Here, we only illustrate an ABC example; for more
complicated ones please refer to the related web site.
