Providing Content Through Web Services

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Providing Content Through Web Services

Saurabh Nandu

May 09 2001

Introduction

We have seen what Web Services are and a Sample Web Service, Stock Quotes, in my previous articles on .NET101 (please refer to these two articles if you need detailed information on Web Services and the tools used). Content Providers will see Web Services as a major component that will change the way they distribute information.

Many Portals like Yahoo and Excite which provide daily updates of News, Sports, Stocks, Games, Weather, E-mail, .... and not to forget Horoscopes (That's what I look up every day to count my chances of emerging as a good programmer!)

The point I want to make here is that, these Portals actually do not create original content for all the sections. They subscribe to some other Portals which provide specialized information. That's the reason why if you surf many such portals you will find that the content of some of their columns like Sports, Weather etc look the same. 

Web sites which offer such specialized information are called "Content Providers", since they provide specialized content to Portals as well as to general surfers.

I have outlined a hypothetical Web Service which such Content Providers could use. Guess what I will be delivering as Content through my Web Service? Horoscopes !

This article will walk through building a sample service that would deliver, Daily Horoscopes. Since I am not a astrologer I will not provide accurate readings nor will I be updating it daily.

Design Considerations

A) Server Side (Portal)

The horoscopes will be updated Daily by the staff. The daily horoscopes will be stored in a XML file called dailyhoro.xml.  The XML database will be placed in a DB subfolder.

B) Clients (Content Consumers)

The clients can view their Horoscopes through Web Pages or through Applications. They will provide the Zodiac sign and the Web Service will process their request and send them their daily readings.

Implementation

First we will see the code for the Web Service. This Service is pretty simple, it takes a string containing the "Zodiac Sign" as a input parameter. Then it looks up its database for the prediction, for the "Zodiac Sign" the client entered. If a match is found then it returns a string containing the Date for which the horoscope applies, along with the prediction for the supplied sign. Just incase you did not know there are 12 zodiac signs Namely - "Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Capricorn, and Sagittarius". You ca write the code in any text editor and save it as wshoro.asmx .

<%@ Webservice Language="C#" class="DailyHoro" %>

using System ;

using System.Web.Services ;

using System.Xml ;

using System.Data;

using System.IO ;

First import the necessary Namespaces.

public class DailyHoro : WebService

{

....

.....
}

We declare a class DailyHoro which extends the WebService class from the System.Web.Services Namespace.

[WebMethod]

public string GetHoro(string zodiac)

{

    return getData(zodiac) ;

}

The class DailHoro contains a public method GetHoro, which is marked with the WebMethod Attribute to indicate it will be available publicly as a  Web Service. This method takes a string containing as the zodiac sign as the input parameter and passes it to another private method getData. The information returned by the getData method is returned to the user. 

private string getData(string zodiac)

{
 
try {
     
//Create a FileStream
     
FileStream fin ; 
     
fin= new FileStream(Server.MapPath("db/dailyhoro.xml"),
     
FileMode.Open, FileAccess.Read,FileShare.ReadWrite );

//Create a DataSet object to contain our Database
     
DataSet ds = new DataSet() ;

//Read the Xml Schema and Data from the stream to the Database file
     
ds.ReadXml(new StreamReader(fin)) ;

//close the stream
     
fin.Close() ;
     
//loop to check for the Zodiac sign provided
     
for(int i=0;i<12 ; i++)  {
        
//Check if the Zodiac sign provided by the user Equals
        
//the "name" field in our Table "zodiac"
        
if(zodiac.Equals(ds.Tables[0].Rows[i]["name"])) {
            
//If a match if found then return the Date and
            
//Prediction
            
string pred =ds.Tables[0].Rows[i]["pred"].ToString() ;
            
string date = ds.Tables[0].Rows[i]["today"].ToString() ;
            
return date+"@"+pred ; 
        
}
     
}

//If no match found then return a error statement
     
return "Wrong Parameter" ;
   
}
   
catch(Exception ed) {
       
return "Read Error!!"+ed.ToString() ;
   
}

}
 
The getData method gets called from the GetHoro method. A FileStream is open to read the XML Database file. Then the DataSet object is used to read the data from the XML file. Next, there is a loop through all the rows of the DataSet to find the match for the Zodiac sign. Once a match is found, the Current date along with the prediction is returned. If no match is found or an error occurs then a relevant message is returned. 

Web Service Deployment

Deploying a Web Service is as simple as deploying any other ASP.NET Web Application. For our example create a Virtual Directory on your computer named "horoservice" or simply upload the files to any server supporting ASP.NET.

Remember to place the "dailyhoro.xml" file in a directory called "db" which should reside in the horoservice virtual directory.

Now your web Service is deployed. To call it just type the URL of the Web Service into your browser i.e http://localhost/horoservice/wshoro.asmx.

Using the Web Service (Consumers)

Since your web service is ready you can now proceed with writing clients to consume your service.

Proxy Class

The first step in creating a client is creating a Proxy Class that contains the information on how to locate the web service and the interface description. We use the WebServiceUtil.exe tool to create a Proxy class.

WebServiceUtil
           
/c:proxy
           
/pa:http://localhost/csharp_test/oroscope/wshoro.asmx?SDL
          
  /n:horo_service

This will create a file "DailyHoro.cs" in the directory from which you ran the tool.
Now compile this source code to generate a Library that we can use in our clients. The library generation command will be.

csc
   
/target:library
   
/r:System.dll;System.Web.Services.dll;System.Net.dll;
           
System.IO.dll;System.Xml.Serialization.dll
   
DailyHoro.cs

Note that you have to reference all the above Assemblies to create your Proxy Library. The above code will generate a Dll "DailyHoro.dll".  Paste the commands in a single command line.

ClientHoro.aspx -The Web Page Client 

Now let's step through the code of a ASP.NET client which will consume the Horoscope Web Service. 

<%@ Import namespace="System" %>

<%@ Import namespace="horo_service" %>

<%@ Page Language="C#" %>

Import the necessary Namespaces. Remember to import the horo_service Namespace too, which contains the Proxy class which we generated in the earlier step.

<html>

<head>
 
<script language="C#" runat="server">

 private void gethoro_Click(object sender, EventArgs e)  {
 
 //Get the Selected Item from the DropDownList
  
string sign = zodiac.SelectedItem.Text;
  
//Create a Instance of the Proxy Class
  
DailyHoro dh = new DailyHoro();
  
//Call the "GetHoro" method of the Web Service on the
  
//Proxy Object. The Proxy object in turn communicates
 
 //to the Web Service. Remember the Proxy cannot do
 
 //anything except act as a bridge between. Your Web
  
//Service and the client. It cannot replace the Web
 
 //Service.
  
string result =dh.GetHoro(sign);
  
//Extract the Date from the Result
  
preddate.InnerHtml = "<b> Horoscope for " +
  
 sign + " as on " + result.Substring(0,10) +
  
 "</b>";
  
//Display the Prediction
  
predspace.InnerHtml=result.Substring(11);

 }
 
</script>

<title>Horoscope Service Client</title>

</head>

In the above code snippet, the gethoro_Click method creates a instance of the class DailyHoro which resides in our proxy library. next the GetHoro method of the DailyHoro class is called and the Zodiac sign is passed as an input parameter. The returned string is split and the date and prediction are displayed separately. 

<body>

<center>

<form runat="server" >
 
<table border="1" width="60%" cellpadding="1" cellspacing="2">
  
<tr>
  
<td colspan=2> <b> Select your Zodiac Sign</b></th>
  
</tr>
  
<tr>
  
<td>
     
<asp:DropDownList id="zodiac" runat="server">
         
<asp:ListItem>aquarius</asp:ListItem>
         
<asp:ListItem>pisces</asp:ListItem>
         
<asp:ListItem>aries</asp:ListItem>
         
<asp:ListItem>taurus</asp:ListItem>
  
<asp:ListItem>gemini</asp:ListItem>
  
<asp:ListItem>cancer</asp:ListItem>
  
<asp:ListItem>leo</asp:ListItem>
  
<asp:ListItem>virgo</asp:ListItem>
  
<asp:ListItem>libra</asp:ListItem>
  
<asp:ListItem>scorpio</asp:ListItem>
  
<asp:ListItem>capricorn</asp:ListItem>
  
<asp:ListItem>sagittarius</asp:ListItem>
     
</asp:DropDownList>
  
</td>
  
</tr>
  
<tr>
  
<td colspan="2" >
     
<asp:Button onClick="gethoro_Click" Text="Fetch !"
   
 runat="server" /></td>
  
</tr>
  
<tr>
      
<td colspan="2"><div id="preddate" runat="server" /></td>
  
</tr>
  
<tr>
      
<td colspan="2"><div id="predspace" runat="server" /></td>
  
</tr>
 
</table>

</form>

</center>

</body>

</html>

The above code is the rest of the code which makes the ASP.NET page. It includes a dropdownlist containing the names of various Zodiac signs, a button which triggers the Web Service and two DIV's to display the returned value.

Deploying the Web Application 

Copy the File ClientHoro.aspx to your Virtual Directory. Also remember to copy the Proxy Dll to your "Bin" directory located in the Virtual Directory. If a "/bin" directory does not exist then create it in your Virtual Directory.

Console Client

HoroClient.cs:   The Horoscope Web Service Consuming Console Client

Now, we will see how to build a Console Application which consumes our Horoscope Web Service.

/*

Compilation

csc /r:System.dll;System.Web.Services.dll;DailyHoro.dll

HoroClient,cs

*/

using System ;

using horo_service ;

//A class which consumes the Web Service

public class HoroClient {
 
public static void Main(string[] argv) {
    
Console.WriteLine("Welcome to Horoscope Client");
    
Console.Write("Enter you Zodiac Sign:");
    
//Read the Input from the user
    
string sign = Console.ReadLine();
    
//Create a instance of the Proxy Class
    
DailyHoro dh = new DailyHoro();
    
//Make a Call on the Web Service Method "GetHoro" and
    
//pass the Zodiac sign to it
    
string result = dh.GetHoro(sign);
    
Console.WriteLine("Horoscope for "+sign+" on " +
 
result.Substring(0,10));
    
//Print the Prediction
    
Console.WriteLine(result.Substring(11));
    
Console.WriteLine("Press Enter to Exit");
    
Console.ReadLine();
 
}

}

In the above example we have a class HoroClient. The Main method of this class takes the Zodiac Sign input from the user and instantiates a object of the type DailyHoro (Contained within the Proxy Library). Next, we call the GetHoro method to get the prediction and display it to the user. 

Deployment

Compile this code and to get the Executable "HoroClient.exe" which consumes our Web Service. Run the file to use the Web Service.