The ASP.NET framework simplifies development of web services. All the low-level work, such as packaging and unpackaging data in XML format and utilizing HTTP protocol to transport the web messages between distributed components, are done by the framework. This allows the developers to focus on the application logic.
The .NET Framework uses asmx as the default file
extension for web services, as opposed to aspx for
Web Forms and ascx for web controls.
All asmx
files start with the
@WebService
directive that instructs ASP.NET on how to compile the code, as well
as the main class name. The WebService directive has the following
attributes:
You can easily create a simple web service similar to the following
asmx file:
<%@ WebService Language="VB" Class="MyClass" %>Public Class MyClass Public Function<WebMethod( )>Add(a as integer, b as integer) as integer Return a + b End function End class
If you prefer to separate your code completely from any ASP.NET
elements, you could have the code for your web service saved in a
separate file and specify the Codebehind attribute
of the @WebService directive to point to the code
file:
<%@ WebService Language="VB" Codebehind="MyClass.vb" Class="MyClass" %>
Public methods of any classes can be tagged with the WebMethod attribute to be made accessible from the Web. The syntax for tagging attributes to methods is different for each .NET language. For example, in C# the tag takes the following form:
[WebMethod(attribute="value" attribute="value" ...)]
public returnType FunctionName(paramsList)In VB, angle brackets are used instead of square brackets, and the tag location is also different:
Public Function <WebMethod(attribute="value" attribute="value" ...)> FunctionName(paramsList) as returnType Public Sub <WebMethod(attribute="value" attribute="value" ...)> SubName(paramsList)
If you are
using Visual Studio.NET,[45] you can
choose Project→Add Web Reference and then type in the URL where
the web service resides. For our purpose, we’ll point to the
web service we created in the last chapter, PubsWS. The URL to this
web service on our server is http://localhost/PubsWS/PubsWS.asmx. After
adding the web reference, you can access the proxy object to the web
service you are calling via the type
servername.proxyObjectName. For your case, it is
localhost.PubsWS.
The following code excerpt demonstrates how to use the web service
through the proxy. We create an instance of the proxy object and then
ask it to relay the message to the real web service to get the list
of authors. The result will be streamed back in XML format, which is
reconstructed into a DataSet object. We then bind
DataGrid1, which is just a DataGrid object that we
have on the Web Form, to the default view of the first table of the
DataSet. Finally, we ask for the actual binding to take place. The
resulting page is the grid populated with rows from the Authors table
of the Pubs sample database.
localhost.PubsWS ws = new localhost.PubsWS( ); DataSet ds = ws.GetAuthors( ); DataGrid1.DataSource = ds.Tables[0].DefaultView; DataGrid1.DataBind( );
Instead of using Visual Studio.NET to locate and automatically generate the proxy class, you can also use the information from the previous chapter to generate the source for the proxy class yourself. You can then include this source or compile the source into a DLL and add the DLL to the project as a reference. In any case, the end result is the same. Here is an example that links against the proxy we created in the previous chapter and fills a grid with data:
<%@ Page Language="C#" %>
<%@ Import Namespace="System.Data" %>
<!-- Link to the proxy generated by wsdl.exe -->
<%@ Assembly Src="PubsWS.cs" %>
<html>
<head>
<title>SOAP Client</title>
</head>
<body>
<!-- Make the SOAP call and fill the data grid. -->
<%
PubsWS ws = new PubsWS( );
DataSet ds = ws.GetAuthors( );
dg.DataSource = ds.Tables[0].DefaultView;
dg.DataBind( );
%>
<!-- Create a data grid. -->
<asp:DataGrid id="dg" runat="server"/>
</body>
</html>