ASPdot.NET: Consuming a WSDL Webservice from ASP

» Home

Consuming a WSDL Webservice from ASP

Click here for the live demo
(Look at the bottom of the homepage)

Last week I exposed my site, 123aspx.com, as a SOAP webservice. However, most webmasters feel you need to run ASP.NET or the SOAP toolkit to take advantage this service. This isn’t necesarily true, with a little ingunetiy and the latest XML parser from Microsoft, you can consume SOAP services from a traditional ASP page. This tutorial will show you how.

Overview
This example application uses the 123aspx.com webservice as an example. I’ll be using the following three files to demonstrate consuming this service from ASP:.

     global.asa — used to populate an Application level variable with the SOAP data when the application starts.
     i_soapcall.asp — an include file used to call the SOAP webservice.
     default.asp — a standard ASP page used to display the formatted SOAP data.

Global.asa
The global.asa file is fired everytime the website starts. Specically the event Sub Application_OnStart is called. Inside of this sub, we are going to populate an application level variable with our SOAP data. Lets take a look at the code.

<SCRIPT LANGUAGE=VBScript RUNAT=Server>
Sub Application_OnStart
    Dim ASPNETResources
    ASPNETResources = GetASPNetResources()
    Application("ASPNETExpires") = 12    ‘set the content to expire in 12 hours.
    If Len(ASPNETResources) >0 then    ‘populate the application level variables
        Application.Lock
        Application("ASPNETResourcesUpdated")=Now()
        Application("ASPNETResourceList")=ASPNETResources
        Application.UnLock
    End if
End Sub
</script>
<!– #include file="i_soapcall.asp" –>

When Application_OnStart first fires, we dimension a variable called ASPNETResources, which is populated by a function call GetASPNetResources(), GetASPNetResources(), found inside of the include file i_soapcall.asp, returns a string of HTML. We will be getting to i_soapcall.asp shortly. Lets go over some of the logic of the global.asa code. Once we have made our function call, we are storing an an expiration time of 12 hours the variable Application("ASPNETExpires"). We’ll use this later in default.asp. We also check to see if the function was sucessful and returned a string with a length greater than 0. If ASPNETResources was populated, then we need to record the time it was populated, Application("ASPNETResourcesUpdated"), and store the results in the application level variable, Application("ASPNETResourceList").

Default.asp
The default.asp is used to display the formatted contents of our webservice request. Let’s start out by looking at the code of default.asp.

<%
Dim     ASPNETResources
If len( Application("ASPNETResourceList") )>0 then    ‘we have our latest resources

    REM — check to see if they expired
    If DateDiff("h",Now(),Application("ASPNETResourcesUpdated")) > Application("ASPNETExpires") Then
        REM — we need to update the latest resurces
        ASPNETResources = GetASPNetResources()
        Application.Lock
        Application("ASPNETResourcesUpdated")=Now()
        Application("ASPNETResourceList")=ASPNETResources
        Application.UnLock
    End if ‘datediff…

Else    ‘for some reason the application level variable is empty, fill it.
    ASPNETResources = GetASPNetResources()
    Application.Lock
    Application("ASPNETResourcesUpdated")=Now()
    Application("ASPNETResourceList")=ASPNETResources
    Application.UnLock

End if
Response.Write     Application("ASPNETResourceList")
%>

The first thing we want to check is to see if our application level variable, Application("ASPNETResourceList"), has been populated. We do that by checking it’s length:

If len( Application("ASPNETResourceList") )>0 then ‘we have our latest resources

If indeed, there is data, we need to check to see if the data has expired. Using the DateDiff function, we can check to see if the data has expired past our timespan of 12 hours which was set in our global.asa as Application("ASPNETExpires").

If DateDiff("h",Now(),Application("ASPNETResourcesUpdated")) > Application("ASPNETExpires") Then

If our data has expired or, if for some reason, Application("ASPNETResourceList") is empty, we call our soap service to populate our variable with data. We are using the same logic that we did in the global.asa. Once we have our data, we execute a Response.Write() to send our formatted results to the client.

Now the Good Stuff – i_soapcall.asp

Now to the heart of the matter, it’s what we’ve all been waiting for, how is this mysterious function GetASPNetResources(), consuming a webservice from legacy ASP? Remeber that our SOAP service is really serving up a XML formatted text file. If we can somehow, progromattically, get to that XML file, then we should be able to parse it. Well in our case, it turns out it’s really not that difficult. Inside of our function, we call two objects:

Function GetASPNetResources()
    Set SoapRequest = Server.CreateObject("MSXML2.XMLHTTP")
    Set myXML =Server.CreateObject("MSXML.DOMDocument")

SoapRequest is the server-side component that can make POST and GET requests across the web. For more info on the MSXML2.XMLHTTP component, you can visit MSDN.

myXML will be used to create an in-memory XML document of our SOAP service. Now that we have our objects, let’s call our SOAP service.

    myXML.Async=False
    SoapURL = "http://64.85.12.73/WebSvc/whatsnew123apx_ds.asmx/GetNew123aspXResources?"
    SoapRequest.Open "GET",SoapURL , False
    SoapRequest.Send()

    if Not myXML.load(SoapRequest.responseXML) then ‘an Error loading XML
        returnString = ""
    Else    ‘parse the XML

First we we set the Asyncronous property of our XMLDocument object to false. This will require the entire SOAP xml document to get loaded into memory before we continue processing code. We set SoapURL to the url of our webservice, and then we open a connection to our webservice using:

SoapRequest.Open "GET",SoapURL , False

SoapRequest.Open takes 5 parameters. Only the first two are required and the remaining three are optional. Here is a breakdown of the 5 parameters:

    oServerXMLHTTPRequest.open bstrMethod, bstrUrl, bAsync, bstrUser, bstrPassword
    Parameters
    bstrMethod
        HTTP method used to open the connection, such as PUT or PROPFIND.
    bstrUrl
        Requested URL. This must be an absolute URL, such as "http://Myserver/Mypath/Myfile.asp".
    bAsync (optional)
        Boolean. Indicator as to whether the call is asynchronous. The default is False (the call does not return immediately).
    bstrUser (optional)
        Name of the user for authentication.
    bstrPassword (optional)
        Password for authentication. This parameter is ignored if the user parameter is Null or missing

With our open connection, we make a request across the web by calling SoapRequest.Send(). The webserver sends the results back, and they are stored in the property SoapRequest.responseXML,as text. We take this text and load it asycronously into an in-memory resident XML Dom object by calling the load method of myXML. If any xml parsing errors occur, the document is not loaded and we decide to return an empty string. If the XML document was loaded successfully, we parse document and look for our data.

Parsing the XML Document

Our SOAP service returns 4 fields: Name, URL, Domain, and DateUpdated. In this version of calling our SOAP service, we are only going to display the Name and URL fields. So how do we get at these fields? We search for them specifiing the XPath syntax for searching.

    REM — The XML Nodes are CASE SENSITIVVE!
    Set nodesURL=myXML.documentElement.selectNodes("//URL")
    Set nodesName=myXML.documentElement.selectNodes("//Name")
    NumOfNodes = nodesURL.Length

The "//" characters are used to denote "find all instances of " in XPath. Therefore, using "//URL" will return an arry of nodes in the XML document named "URL". We have to be careful here, because XML is case sensitive, calling "//url" will not return any nodes at all. We check the length of the array by calling nodesURL.Length.

The Hard Part is Over

We’ve called our SOAP service, and now we have access to our nodes, all that’s left is to format and display it to the HTML client.

    ResourceList = "<font face=verdana size=2>Latest ASP.NET Resources</font><ul>"
    For i = 0 to NumOfNodes -1
        ResourceList = ResourceList & "<li><a href=" & nodesURL(i).text & "><font face=verdana size=2>" & nodesName(i).text & "</font></a></li>"
    next
    ResourceList =ResourceList & "</ul>"
    returnString = ResourceList
    GetASPNetResources = returnString

Because the array of nodes is a zero based array, we run a For loop to a maximum of NumOfNodes -1. We dynamically build a string, wrapping <li> </li> around our Names and URLs. We could have easily have built an HTML table or some other structure. We store our formatted HTML string in returnString, and pass returnString back to the function call GetASPNetResources = returnString.

A screen shot of our formatted results.

That’s All!

That’s all their is to calling a SOAP service from a legacy ASP page. We’ve called our SOAP service and passed it into an XML object using Microsoft’s parsers:
MSXML2.XMLHTTP and MSXML.DOMDocument. We’ve looped through the collection of nodes and created an HTML formatted string. We’ve simulated ASP.NET caching by storing the HTML formatted string in an Application level varable. Here is the code in its entirety.

All the code

Global.asa

<SCRIPT LANGUAGE=VBScript RUNAT=Server>

Sub Application_OnStart
    Dim ASPNETResources

    ASPNETResources = GetASPNetResources()
    Application("ASPNETExpires") = 12    ‘set the content to expire in 12 hours.
    If Len(ASPNETResources) >0 then    ‘populate the application level variables
        Application.Lock

        Application("ASPNETResourcesUpdated")=Now()
        Application("ASPNETResourceList")=ASPNETResources
        Application.UnLock
    End if

End Sub
</script>
<!– #include file="i_soapcall.asp" –>

Default.asp

<%@ Language=VBScript %>
<%Option Explicit%>
<!– #include file="i_soapcall.asp" –>
<HTML>
<HEAD>
<META NAME="GENERATOR" Content="Microsoft Visual Studio 6.0">
</HEAD>
<BODY>
<%
Dim     ASPNETResources
If len( Application("ASPNETResourceList") )>0 then    ‘we have our latest resources

    REM — check to see if they expired
    If DateDiff("h",Now(),Application("ASPNETResourcesUpdated")) > Application("ASPNETExpires") Then
        REM — we need to update the latest resurces
        ASPNETResources = GetASPNetResources()
        Application.Lock
        Application("ASPNETResourcesUpdated")=Now()
        Application("ASPNETResourceList")=ASPNETResources
        Application.UnLock
    End if ‘datediff…

Else    ‘for some reason the application level variable is empty, fill it.
    ASPNETResources = GetASPNetResources()
    Application.Lock
    Application("ASPNETResourcesUpdated")=Now()
    Application("ASPNETResourceList")=ASPNETResources
    Application.UnLock

End if ‘len(..

Response.Write     Application("ASPNETResourceList")

%>
<P> </P>

</BODY>
</HTML>

i_soapcall.asp