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ASP.NET Web Service

Question Posted / hanmantkendre


ASP.NET Web Service..

Answer / hanmantkendre

Introduction

We can now use ASP.NET to create Web Service that is based
on industrial standards included XML, SOAP and WSDL.

ASP.NET Web Services support clients using HTTP-POST,
HTTP-GET and SOAP protocols to invoke methods exposed,
depends on your specific requirement you choose one method
over the others. The main difference between HTTP-GET or
HTTP-POST and SOAP is the data types supported by SOAP is
much richer because SOAP used XSD schema to represent
complex data types.

Here are samples codes I use to test the building of ASP.NET
Web Service:
Step 1: Create the ASP.NET Web Service Source File

ASP.NET Web Service file name has extension asmx and my file
is named MyWebService.asmx, source is listed as follows:
File: MyWebService.asmx
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<%@ WebService Language="C#" class="MyClass" %>

using System.Web.Services ;

public class MyClass
{
[WebMethod()]
public int Add ( int a, int b)
{
return a + b ;
}
}

The page directive WebService is required and class is the
name of the .NET Class to expose the Web Service, each
method exposes as Web Service Class Method need to have a
declarative attribute statement [WebMethod()] in front of
it. Here the .NET Class implementation is included in the
same file with ASP.NET Web Service file but it is not
mandatory and we can choose to include an external .NET
Assembly to implement the service as the following example:
File: MyWebService2.asmx
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<%@ WebService Language="C#"
class="MyWebService.MyStringReverse, MyWebServiceImpl" %>

The file MyWebService2.asmx is referencing another .NET
Assembly MyWebServiceImpl which is located under the /bin
ASP.NET Application sub-folder (note that the default
location for Assemblies in ASP.NET is /bin sub-folder under
each ASP.NET Applications). The source of .NET Assembly
MyWebServiceImpl is written by C# and is listed as follows:
File: MyWebServiceImpl.cs
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namespace MyWebService
{
using System ;
using System.Web.Services ;

public class MyStringReverse: WebService
{
[WebMethod(Description="Reverse String")]
public String ReverseString ( String InString )
{
// Check null String
if ( InString == null ) return null ;

Int32 intSize = InString.Length ;
char[] arrayInString = InString.ToCharArray() ;
char[] arrayOutString = new char[intSize] ;

for (Int32 i = 0 ; i < intSize ; ++i)
arrayOutString[i] =
arrayInString[intSize-i-1] ;

return new String(arrayOutString) ;
}
}
}

To create the Assembly, you can use the following command:
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C:\>CSC /t:library /out:bin/MyWebServiceImpl.dll
MyWebServiceImpl.cs

The following sections I will continue use MyWebService.asmx
as my experimental Web Service.
Step 2: Create the ASP.NET Web Service Clients

There are many ways to consume Web Services and have three
examples. The first one uses HTTP-POST protocol and it has
advantage to coexist with today’s application quite well and
use HTTP-GET is similar and I let reader to try it. The
second one uses SOAP Proxy Client Object generated by WSDL
utility and it provides programmers with their familiar
object modal that they call methods provided by the
generated Proxy Interface. The final one uses SOAP standard
request message and it parses SOAP response message with the
help of XMLHTTP COM object that is installed by Microsoft
XML Parser 3.0.
Client use HTTP-POST Method

The example is an ASP.NET page TestWebService.aspx and
source listing as follows:
File: TestWebService.aspx
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<html>

<body>
<form
action="http://localhost/ASP.NET/MyWebService.asmx/Add"
method="POST">

<input name="a"></input>
<input name="b"></input>

<input type="submit" value="Enter"> </input>
</form>

</body>
</html>

The ASP page accepts parameters from browser and calls the
Add method of the Web Service MyWebService via the HTTP-POST
protocol, the result will be XML message and need further
parsing by the client application. To parse the response,
client can use either Java XML parser in applet or use IE5’s
DOM Object.

The following is an example of XML response when parameters
a=1, b=2 are inputted:
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<?xml version="1.0" encoding="utf-8" ?>
<int xmlns="http://tempuri.org/">3</int>

Client use WSDL Generated Proxy Object

If your client will be Windows applications or ASP.NET
applications, you can use WSDL.EXE utility to created
standard .NET Assemble to provide Proxy Class for your clients.

Here are steps you can follow and try:

Use WSDL.EXE utility to create the Proxy Class source file
in any language you have chosen and here I use C# and
command as follows:
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C:\>wsdl /language:C# /out:MyProxyClass.cs
http://localhost/ASP.NET/MyWebService.asmx

MyProxyClass.cs is generated and source listing as follows:
File: MyProxyClass.cs
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//------------------------------------------------------------------------------
// <autogenerated>
// This code was generated by a tool.
// Runtime Version: 1.0.2914.16
//
// Changes to this file may cause incorrect behavior and
will be lost if
// the code is regenerated.
// </autogenerated>
//------------------------------------------------------------------------------

//
// This source code was auto-generated by wsdl,
Version=1.0.2914.16.
//
using System.Diagnostics;
using System.Xml.Serialization;
using System;
using System.Web.Services.Protocols;
using System.Web.Services;

[System.Web.Services.WebServiceBindingAttribute(Name="MyClassSoap",
Namespace="http://tempuri.org/")]
public class MyClass :
System.Web.Services.Protocols.SoapHttpClientProtocol {

[System.Diagnostics.DebuggerStepThroughAttribute()]
public MyClass() {
this.Url = "http://localhost/ASP.NET/MyWebService.asmx";
}

[System.Diagnostics.DebuggerStepThroughAttribute()]

[System.Web.Services.Protocols.SoapDocumentMethodAttribute("http://tempuri.org/Add",


Use=System.Web.Services.Description.SoapBindingUse.Literal,

ParameterStyle=System.Web.Services.Protocols.SoapParameterStyle.Wrapped)]
public int Add(int a, int b) {
object[] results = this.Invoke("Add", new object[] {
a,
b});
return ((int)(results[0]));
}

[System.Diagnostics.DebuggerStepThroughAttribute()]
public System.IAsyncResult BeginAdd(int a, int b,
System.AsyncCallback callback, object asyncState) {
return this.BeginInvoke("Add", new object[] {
a,
b}, callback, asyncState);
}

[System.Diagnostics.DebuggerStepThroughAttribute()]
public int EndAdd(System.IAsyncResult asyncResult) {
object[] results = this.EndInvoke(asyncResult);
return ((int)(results[0]));
}
}

Then we need to create the .NET Assembly for used by clients:
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C:\> csc /t:library MyProxyClass.cs

The above command will compile the source and create
MyProxyClass.dll library file.

I use ASP to depict how to use the proxy object and the file
is TestWebServiceWithProxy.aspx source listing as follows:
File: TestWebServiceWithProxy.aspx
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<%@ page language="C#" %>
<html>
<script runat="server">
void btn_click(Object source, EventArgs e)
{
MyClass mycls = new MyClass() ;
int x = Int32.Parse(a.Text) ;
int y = Int32.Parse(b.Text);

Message.Text = mycls.Add( x, y).ToString() ;
}
</script>

<body>
<form Action = "TestWebServiceWithProxy.aspx" runat="server">
<asp:TextBox id="a" runat="server" />
<asp:TextBox id="b" runat="server" />
<asp:button id=btn OnClick="btn_click" Text="Enter"
runat="server" />
<p><asp:label id="Message" runat="server" /></P>
</form>
</body>
</html>

Client use XMLHTTP to call Web service via SOAP

To fully explore the SOAP capability, you may choose to call
your ASP.NET Web Service via SOAP core protocol and here I
provide another example for reference.

To test the ASP.NET service with SOAP protocol, I create an
ASP client file TestWebServiceByXML.asp and its source is
listed as follows:
File: TestWebServiceByXML.asp
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<html>
<body>
<script language="jscript">
function btn_click (a, b)
{
var xmlObj = new
ActiveXObject("Msxml2.DOMDocument") ;
var sXml = "<?xml version=\"1.0\" ?>" ;
sXml += "<soap:Envelope "
sXml +=
"xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" " ;
sXml +=
"xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" " ;
sXml +=
"xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">" ;
sXml += "<soap:Body>" ;
sXml += "<Add
xmlns=\"http://tempuri.org/\">" ;
sXml = sXml + "<a>" + a.value + "</a>" ;
sXml = sXml + "<b>" + b.value +
"</b>" ;
sXml +=
"</Add></soap:Body></soap:Envelope>"

// Try to parse the XML string into DOM object
xmlObj.loadXML(sXml) ;

//To see the validated XML string is well-formed
XmlRequest.innerText = xmlObj.xml ;

var xmlHTTP = new
ActiveXObject("Msxml2.XMLHTTP") ;
xmlHTTP.Open ( "Post",
"http://localhost/ASP.NET/MyWebService.asmx", false) ;
xmlHTTP.setRequestHeader("SOAPAction",
"http://tempuri.org/Add") ;
xmlHTTP.setRequestHeader("Content-Type",
"text/xml; charset=utf-8" ) ;
xmlHTTP.Send(xmlObj.xml) ;
MyResult.innerText = xmlHTTP.responseText ;

var xmlResponse = xmlHTTP.responseXML ;
answer.innerText =
xmlResponse.selectSingleNode("soap:Envelope/soap:Body/AddResponse/AddResult").text
;
}
</script>

<form>
<p>Please input a:<input id="a" name="a"></input></p>
<p>Please input b:<input id="b" name="b"></input></p>
<p>
<input type="button" id="btn" value="Enter"
onclick="jscript:btn_click(a, b)"></input>
</p>
<p>Answer is <span id="answer"></span></p>
<hr></hr>
<p>Request:</p>
<span id="XmlRequest"></span>
<p>Response:</p>
<span id="MyResult"></span>

</form>

</body>
</html>

Here I installed Microsoft XML Parser 3.0 in my client
machine that give me the XMLHTTP and DOM COM objects to test
my application.
Summary

There are many difference implementations for SOAP Service
but the standard is there and we can start to build some
useful applications on it. Although ASP.NET or SOAP web
services have many nice features, if you want to consume the
exposed Web Services in you clients, please make sure you
have the latest libraries installed because standards
continue evolving and all vendors try their best achieve the
edge in such open standards war.

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