Published: Wednesday, July 03, 2002
Integrating ASP.NET XML Web Services with 'Classic' ASP Applications
By Paul Bunting
Introduction
Microsoft is investing millions in promoting .NET and its advantages. One
of the many plugged advantages of the Microsoft .NET initiative is XML Web
Services – the ability to remove your business logic from custom DLLs and
COM/DCOM components (helping to avoid DLL hell) and hosting your middle tier
business logic as Web Services, which can be accessed by all your
applications (Web Sites, Distributed Applications, etc.) (see
this article
for more information on creating and consuming Web Services in .NET). But how do you use
some of these new Web Services you have developed in a staggered upgrade of
your existing 'Classic' ASP Applications?
This article intends to illustrate how to consume Web Services written with .NET through a classic
ASP page. By placing an application's business logic in a Web Service abstraction layer, and by being
able to consume Web Services through classic ASP pages, one can have their
existing ASP Web applications share the same business logic as ASP.NET applications on the same Web server.
This can be especially helpful if an existing ASP application works fine and you do not have the time
to fully port it to ASP.NET, but you still wish it to be able to work in close synchrony with that new
ASP.NET application you're programming.
The example for this article is based on a real-world need: when conducting business to business
eCommerce you sometimes need to calculate special discounts for regular customers in order to secure their
business. In this article we will create a Web Service that will calculate the special
discount allocated to a business. We will finish by integrating this Web Service into a
simple classic ASP application!
The Database
For this article I will be using the Northwinds database available in Microsoft Access.
I had to make a small change to the Northwinds database Products table's structure:
specifically I added a CostPrice field of type money (which I then populated with some
random amounts). (The altered Northwinds database is available in the
code download.)
The Web Service
As discussed in Creating and Consuming
a Web Service, Web Services can be created with any text editor, such as the
Web Matrix Project, Visual Studio .NET,
or others. In this article I will be examining how to create a Web Service using Visual Studio .NET.
To start, create a new ASP.NET Web Project from within Visual Studio.NET.
Next, delete the default Web form it adds and then add a new Web Service
file (named eCommerce.asmx - the Web Service itself being named eCommerce).
Within the Web Service file change the default namespace to
ClassicASP_nDotNET.eCommerce and then add the Web method
CalculateDiscountCompanyX.
The Web Method CalculateDiscountCompanyX is a simple function that will
be used to calculate the business discount for CompanyX. (Clearly a more robust solution would be to
create a more generic method, like CalculateDiscount(CompanyID), where
CompanyID uniquely identified a company. Then, a database lookup could be performed
to determine the discount(s) the company enjoys, if any. However, this article focuses on integrating
.NET Web Services with existing classic ASP application.)
For our application, let's assume that there is a minimum discount for CompanyX (set at 10%),
as well as a safety net of cost +7.5% as a minimum profit
for our business. Both the company's discount and our desired profit are hard coded into the Web
method (again, not very robust, but we're focusing on integration here).
The CalculateDiscountCompanyX Web method is fairly simple, taking the following input
parameters:
UnitPrice - the recommended retail price (RRP) (type Double)CostPrice - the actual cost of the product (i.e., how much our company had to pay to get the product) (type Double)AccessCode - a password for security of web service (type String)
Upon error the CalculateDiscountCompanyX Web method returns a negative value. The source code
for the method can be seen below:
' the web method
<WebMethod()> _
Public Function CalculateDiscountCompanyX(ByVal UnitPrice As Double, _
ByVal CostPrice As Double, _
ByVal AccessCode As String) As Double
Dim dblDiscount As Double, _
dblMarkup As Double, _
dblMinMarkup As Double, _
dblMinClientDiscount As Double
dblMarkup = (1.3) ' our desired markup percentage (30%)
dblMinMarkup = (1.075) ' our min markup (7.5%)
' the desired minimum discount for our customer (10%)
dblMinClientDiscount = (0.1)
Try
If AccessCode = "p455w0rd" Then
' dblDiscount - Calculates discount based on the markup percentage
' supplied.
dblDiscount = FormatNumber(((UnitPrice - (CostPrice * dblMarkup))), 2)
' check discount is greater than the minimum
If dblDiscount + 0 <= (UnitPrice * dblMinClientDiscount) Then
dblDiscount = FormatNumber((UnitPrice * dblMinClientDiscount), 2)
End If
' Check price does not go too low - if it is
' make sure we get our min margin
If (UnitPrice - dblDiscount) <= (CostPrice * dblMinMarkup) Then
dblDiscount = FormatNumber((UnitPrice - (CostPrice * dblMinMarkup)), 2)
End If
Return dblDiscount
Else
Return -1 'invalid password
End If
Catch ex As Exception
Return -1 'eep, an exception was thrown
End Try
End Function
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Integrating your .NET Web Service into Existing Classic ASP Applications
To make it a lot easier to get your classic ASP pages to talk to .NET Web Services
you should download and install the MS SOAP Toolkit
2.0. This will allow you to talk to your new web services using SOAP – which is a lot
easier than a few of the other methods you may think of trying. In fact, there is an article
here on 4Guys that illustrates how to use the SOAP Toolkit -
Creating Web Services using ASP. (The Creating Web Services using ASP
article shows how to produce and consume Web Services in classic ASP through the use of two VB COM components
that utilize the SOAP Toolkit. In this article I'll demonstrate how to use the SOAP Toolkit to consume
a .NET Web Service directly through a classic ASP page.)
The ASP page utilizes the Web Service we just created to calculate the discount for CompanyX for a
given product. To make coding and maintenance easier I like to remove the SOAP call
from the main bulk of the code and put it into its own function (CalculateDiscount),
which is shown below. Since the CalculateDiscount function uses the SOAP Toolkit, only
a few lines of code are needed to call the Web Service.
Public Function CalculateDiscount(UnitPrice, CostPrice)
SET objSoapClient = Server.CreateObject("MSSOAP.SoapClient")
objSoapClient.ClientProperty("ServerHTTPRequest") = True
' needs to be updated with the url of your Web Service WSDL and is
' followed by the Web Service name
Call objSoapClient.mssoapinit("http://localhost/ClassicASP_n_DotNET/" & _
"eCommerce.asmx?WSDL", "eCommerce")
' use the SOAP object to call the Web Method Required
CalculateDiscount = objSoapClient.CalculateDiscountCompanyX(UnitPrice, _
CostPrice, "p455w0rd")
End Function
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This function is fairly straightforward. The mssoapinit call readies the Web Service
call by interrogating the WSDL of the Web Service. (For more information on what WSDL, read
this article.)
Next, the actual Web method CalculateDiscountCompanyX is called, passing in the
UnitPrice and CostPrice parameters. The discount value is returned by the Web
Service and then returned by the CalculateDiscount function.
In the classic ASP page where the above function is found (companyx_products.asp in the
code download), it is called once for every item in the
Northwinds Products table. Essentially, the ASP page loops through the rows in the
Products table, calling the CalculateDiscount function for each row and
displaying the discount for CompanyX.
Conclusion
This article has shown how one can build a classic ASP page to communicate with a .NET Web Service.
Additionally, note that by placing business logic into a Web Service abstraction layer, one
can have existing ASP applications on a Web server share the business logic rules with
ASP.NET pages seamlessly.
Happy Programming!
By Paul Bunting
http://www.developtheweb.co.uk/
Attachments
Download the code (as an MSI file in ZIP format)
