Interview Questions and Answers on .Net Framework C#.Net (Part-2)

Interview Questions and Answers on .Net Framework and C#.Net

Question 40 – What are the Advantages of XML Serialization? 

• Serialization is of XML based. 

• Support for cross-platform programming. 

• Easily readable and editable. 

Question 41 – What is Custom Serialization? 

• In some cases, the default serialization techniques provided by .NET may not be sufficient in real life. • This is when we require implementing custom serialization. 

• It is possible to implement custom serialization in .NET by implementing the ISerializable interface. 

• This interface allows an object to take control of its own serialization and de-serialization process. 

• It gives us a great deal of flexibility in the way we can save and restore objects. 

Question 42 – What is a Namespace? 

• Containers of objects which contain classes, unions, structures, interfaces, enumerators, delegates. 

• Main goal is for creating a hierarchical organization of the program. 

• Developers do not need to worry about the naming conflicts of classes, functions, variables etc. 

Question 43 – What is GUID? 

It is a Short form of Globally Unique Identifier, A unique 128-bit number that is produced by the Windows OS or Windows app to identify a particular component, application, file, database entry, and/or user. 

Question 44 – What is a Formatter? 

• A formatter is used to determine the serialization format for objects. 

• In other words, it is used to control the serialization of an object to and from a stream. 

• They are the objects that are used to encode and serialize data into an appropriate format before they are transmitted over the network. 

• They expose an interface called the IFormatter interface. IFormatter’s significant methods are Serialize and De-serialize which perform the actual serialization and de-serialization. 

• There are two formatter classes provided within .NET, the BinaryFormatter and the SoapFormatter. Both these classes extend the IFormatter interface. 

Question 45 – What is a Binary Formatter? 

The Binary formatter provides support for serialization using binary encoding. The BinaryFormater class is responsible for binary serialization and is used commonly in .NET’s Remoting technology. This class is not appropriate when the data is supposed to be transmitted through a firewall. 

Question 46 – What is SOAP Formatter? 

The SOAP formatter provides formatting that can be used to serialize objects using the SOAP protocol. It is used to create a Soap envelope and it uses an object graph to generate the result. It is responsible for serializing objects into SOAP messages or parsing the SOAP messages and extracting these serialized objects from the SOAP messages. SOAP formatters in .NET are widely used by Web Services. 

Question 47 – What is Reflection? 

• It is a collection of classes which allow u to query assembly (class/object) metadata at runtime. 

• Using reflection we can also create new types and their instances at runtime and invoke methods on these new instances. 

• At runtime, the Reflection mechanism uses the PE file to read information about the assembly. 

• We can dynamically invoke methods using the System.Type.Invokemember 

• We can dynamically create types at runtime using System.Reflection.Emit.TypeBuilder 

• With reflection we can do the below 

• we can dynamically create an instance of a type 

• bind the type to an existing object 

• get the type from an existing object 

• invoke its methods or access its fields and properties 

Question 48 – What are Thread and Process? 

• Threads are basically lightweight processes responsible for multitasking within a single application. 

• The base class used for threading is System.Threading. 

• Threads are implemented when situations in which you want to perform more than one task at a time. • A Process is an instance of a running application. 

• A thread is the Execution stream of the Process. 

• A process can have multiple Threads. 

• Example: A Microsoft Word is an Application. When you open a word file, an instance of the Word starts and a process is allocated to this instance which has one thread. 

• Create Thread – use System.Thread() class and create an instance. 

• Join Thread – use object.Join() to join threads. 

• Suspend Thread – use object.Sleep() to suspend a thread. 

• Kill Thread – use object.Abort() to abort a thread. 

 Question 49 – What are the difference between a DLL and an Exe? 

DLL	EXE
Create an object of dll	Not in exe
Multiple Uses	Single use
Cannot be started as stand alone	Can be started as stand alone

Question 50 – What are Globalization and Localization? 

To implementing a multilingual user interface, you design the user interface to open in the default UI language and offer the option to change to other languages. Globalization is the first step in the process. A globalized application supports localized user interfaces and regional data for all users. Truly global applications should be culture-neutral and language-neutral. A globalized application can correctly accept, process, and display a worldwide assortment of scripts, data formats, and languages. Accommodating these cultural differences in an application is called localization. 

Question 51 – What is a Resource File?

Resource files are the files containing data that is logically deployed with an application. These files can contain data in a number of formats including strings, images and persisted objects. It has the main advantage of If we store data in these files then we don’t need to compile these if the data get changed. In .NET we basically require them storing culture-specific information’s by localizing application’s resources. You can deploy your resources using satellite assemblies. 

Question 52 – What is Code Access Security(CAS)?

CLR allows code to perform only those operations that the code has permission to perform. So CAS is the CLR’s security system that enforces security policies by preventing unauthorized access to protected resources and operations. Using the Code Access Security, you can do the following: 

• Restrict what your code can do 

• Restrict which code can call your code 

• Identify code Code access security consists of the following elements: 

• Permissions – represent access to a protected resource or the ability to perform a protected operation. 

• Permission sets – A permission set is a collection of permissions. 

• Code groups – a logical grouping of code that has a specified condition for membership Evidence 

• Policy – Security policy is the configurable set of rules that the CLR follows when determining the permissions to grant to code. 

• There are four policy levels – Enterprise, Machine, User, and Application Domain, each operating independently from each other. Syntax 

• See CAS objects — Run ‘caspol -lg’ from command line. 

• Add CAS objects — caspol -ag 1.3 -site www.mydomain.com FullTrust 

• Change CAS obj — caspol -cg 1.3 FullTrust 

• Turn Off — caspol -s off 

Question 53 – What is difference between Code Based Security and Role Based Security? 

CAS is the approach of using permissions and permission sets for a given code to run. Example, Admin can disable running executables off the Internet or restrict access to corporate database to only few applications. 

• Role security most of the time involves the code running with the privileges of the current user. This way the code cannot supposedly do more harm than mess up a single user account. 

• Neither is better. It depends on the nature of the application; both code-based and role-based security could be implemented to an extent. 

Question 54 – What is difference between Invoke and Begin Invoke 

• Delegate.Invoke: Executes synchronously, on the same thread. 

• Delegate.BeginInvoke: Executes asynchronously, on a thread pool thread. 

• Control.Invoke: Executes on the UI thread, but calling thread waits for completion before continuing. • Control.BeginInvoke: Executes on the UI thread, and calling thread doesn’t wait for completion. 

• BeginInvoke is asynchronous. When BeginInvoke is called from the UI thread the request will be executed in parallel with the UI thread. Which means it may not execute until after the currently executing method has returned. So in this case the text box will never appear to update because the for loop will not be interrupted, as the calling thread will not wait for this event to be completed before continuing. 

• Alternatively, Invoke is synchronous. The text box will be updated because the calling thread will wait for the call to complete before continuing execution. 

Question 55 – What is the difference between Debug and Trace? 

Tracing is actually the process of collecting information about the program’s execution. Debugging is the process of finding & fixing errors in our program. Tracing is the ability of an application to generate information about its own execution. Trace and Debug work in a similar way, the difference is that tracing from the Debug class only works in builds that have the DEBUG symbol defined, whereas tracing from the Trace class only works in builds that have the TRACE symbol defined. 

• Use System.Diagnostics.Trace.WriteLine for tracing that you want to work in debugging and release builds 

• Use System.Diagnostics.Debug.WriteLine for tracing that you want to work only in debug builds.

 Question 56 – What is a Debug version of code? 

• Preprocessor(Debugging Diagnostic) macro _DEBUG is enabled. 

• More memory size. 

• Support files required. (MFC Dll’s) 

• No Code Optimization 

• Uses MFC Debug Library 

• ASSERT is enabled. 

• Execution takes more time 

Question 57 – What is a Release version of a code? 

• Preprocessor(Debugging Diagnostic) macro NDEBUG is enabled. 

• Less memory size. 

• Support files not required. (MFC Dll’s) 

• Code Optimization 

• Uses MFC Release Library 

• ASSERT is disabled anything inside of ASSERT will not be executed. 

• Execution takes less time 

Question 58 – What is an IDisposable Interface? 

• The primary use of this interface is to release unmanaged resources. The garbage collector automatically releases the memory allocated to a managed object when that object is no longer used. 

• However, it is not possible to predict when garbage collection will occur. 

• Furthermore, the garbage collector has no knowledge of unmanaged resources such as window handles, or open files and streams. 

• The consumer of an object can call this method when the object is no longer needed. 

Question 59 – What is Finalize block in .net? 

• Finalize() is called by the runtime 

• Is a C# equivalent of destructor, called by Garbage Collector when the object goes out of scope. 

• Implement it when you have unmanaged resources in your code, and want to make sure that these resources are freed when the Garbage collection happens. 

• Finalize() can NOT be overridden or called in C#. 

• Since, Finalize() is called by the Garbage Collector, it is non-deterministic. 

Question 60 – What is Dispose block in .net? 

• Dispose() is called by the user 

• Same purpose as finalize, to free unmanaged resources. However, implement this when you are writing a custom class, that will be used by other users. 

• Overriding Dispose() provides a way for user code to free the unmanaged objects in your custom class. 

• Dispose() has to be implemented in classes implementing IDispose interface. 

• Dispose() method is called explicitly in the code itself.

Introduction Web services 1.0

Introduction Web services 

Web services are open standard ( XML, SOAP, HTTP etc.) based Web applications that interact with other web applications for the purpose of exchanging data

Web Services can convert your existing applications into Web-applications.

In this tutorial you will learn what exactly Web Services are and Why and How to use them.

What are Web Services

Few definitions are given here and all the definitions are correct.

• A web service is any piece of software that makes itself available over the internet and uses a standardized XML messaging system. XML is used to encode all communications to a web service. For example, a client invokes a web service by sending an XML message, then waits for a corresponding XML response. Because all communication is in XML, web services are not tied to any one operating system or programming language--Java can talk with Perl; Windows applications can talk with Unix applications.
• Web Services are self-contained, modular, distributed, dynamic applications that can be described, published, located, or invoked over the network to create products, processes, and supply chains. These applications can be local, distributed, or Web-based. Web services are built on top of open standards such as TCP/IP, HTTP, Java, HTML, and XML.
• Web services are XML-based information exchange systems that use the Internet for direct application-to-application interaction. These systems can include programs, objects, messages, or documents.
• A web service is a collection of open protocols and standards used for exchanging data between applications or systems. Software applications written in various programming languages and running on various platforms can use web services to exchange data over computer networks like the Internet in a manner similar to inter-process communication on a single computer. This interoperability (e.g., between Java and Python, or Windows and Linux applications) is due to the use of open standards.

To summarize, a complete web service is, therefore, any service that:

• Is available over the Internet or private (intranet) networks
• Uses a standardized XML messaging system
• Is not tied to any one operating system or programming language
• Is self-describing via a common XML grammar
• Is discoverable via a simple find mechanism

Components of Web Services?

The basic Web services platform is XML + HTTP. All the standard Web Services works using following components

• SOAP (Simple Object Access Protocol)
• UDDI (Universal Description, Discovery and Integration)
• WSDL (Web Services Description Language)

All these components have been discussed in Web Services Architecture section.

How Does it Work?

You can build a Java-based Web Service on Solaris that is accessible from your Visual Basic program that runs on Windows. You can also use C# to build new Web Services on Windows that can be invoked from your Web application that is based on JavaServer Pages (JSP) and runs on Linux.

An Example

Consider a simple account-management and order -processing system. The accounting personnel use a client application built with Visual Basic or JSP to create new accounts and enter new customer orders.

The processing logic for this system is written in Java and resides on a Solaris machine, which also interacts with a database to store the information.

The steps illustrated above are as follows:

1. The client program bundles the account registration information into a SOAP message.
2. This SOAP message is sent to the Web Service as the body of an HTTP POST request.
3. The Web Service unpacks the SOAP request and converts it into a command that the application can understand. The application processes the information as required and responds with a new unique account number for that customer.
4. Next, the Web Service packages up the response into another SOAP message, which it sends back to the client program in response to its HTTP request.
5. The client program unpacks the SOAP message to obtain the results of the account registration process. For further details regarding the implementation of Web Services technology, read about the Cape Clear product set and review the product components.

Why Web Services ?

Here are the benefits of using Web Services

• Exposing the existing function on to network:

  A Web service is a unit of managed code that can be remotely invoked using HTTP, that is, it can be activated using HTTP requests. So, Web Services allows you to expose the functionality of your existing code over the network. Once it is exposed on the network, other application can use the functionality of your program.

• Connecting Different Applications ie Interoperability:

  Web Services allows different applications to talk to each other and share data and services among themselves. Other applications can also use the services of the web services. For example VB or .NET application can talk to java web services and vice versa. So, Web services is used to make the application platform and technology independent.

• Standardized Protocol:

  Web Services uses standardized industry standard protocol for the communication. All the four layers (Service Transport, XML Messaging, Service Description and Service Discovery layers) uses the well defined protocol in the Web Services protocol stack. This standardization of protocol stack gives the business many advantages like wide range of choices, reduction in the cost due to competition and increase in the quality.

• Low Cost of communication:

  Web Services uses SOAP over HTTP protocol for the communication, so you can use your existing low cost internet for implementing Web Services. This solution is much less costly compared to proprietary solutions like EDI/B2B. Beside SOAP over HTTP, Web Services can also be implemented on other reliable transport mechanisms like FTP etc.
  
  
  Services Behavioral Characteristics

  Web services have special behavioral characteristics XML-based Web Services uses XML at data representation and data transportation layers. Using XML eliminates any networking, operating system, or platform binding. So Web Services based applications are highly interoperable application at their core level. Loosely coupled A consumer of a web service is not tied to that web service directly. The web service interface can change over time without compromising the client's ability to interact with the service. A tightly coupled system implies that the client and server logic are closely tied to one another, implying that if one interface changes, the other must also be updated. Adopting a loosely coupled architecture tends to make software systems more manageable and allows simpler integration between different systems. Coarse-grained Object-oriented technologies such as Java expose their services through individual methods. An individual method is too fine an operation to provide any useful capability at a corporate level. Building a Java program from scratch requires the creation of several fine-grained methods that are then composed into a coarse-grained service that is consumed by either a client or another service. Businesses and the interfaces that they expose should be coarse-grained. Web services technology provides a natural way of defining coarse-grained services that access the right amount of business logic. Ability to be synchronous or asynchronous Synchronicity refers to the binding of the client to the execution of the service. In synchronous invocations, the client blocks and waits for the service to complete its operation before continuing. Asynchronous operations allow a client to invoke a service and then execute other functions. Asynchronous clients retrieve their result at a later point in time, while synchronous clients receive their result when the service has completed. Asynchronous capability is a key factor in enabling loosely coupled systems. Supports Remote Procedure Calls (RPCs) Web services allow clients to invoke procedures, functions, and methods on remote objects using an XML-based protocol. Remote procedures expose input and output parameters that a web service must support. Component development through Enterprise JavaBeans (EJBs) and .NET Components has increasingly become a part of architectures and enterprise deployments over the past couple of years. Both technologies are distributed and accessible through a variety of RPC mechanisms. A web service supports RPC by providing services of its own, equivalent to those of a traditional component, or by translating incoming invocations into an invocation of an EJB or a .NET component. Supports document exchange One of the key advantages of XML is its generic way of representing not only data, but also complex documents. These documents can be simple, such as when representing a current address, or they can be complex, representing an entire book or RFQ. Web services support the transparent exchange of documents to facilitate business integration.

  Web Services Architecture

  There are two ways to view the web service architecture.

  • The first is to examine the individual roles of each web service actor.
  • The second is to examine the emerging web service protocol stack.

  1. Web Service Roles

  There are three major roles within the web service architecture:

  • Service provider:
    This is the provider of the web service. The service provider implements the service and makes it available on the Internet.
  • Service requestor
    This is any consumer of the web service. The requestor utilizes an existing web service by opening a network connection and sending an XML request.
  • Service registry
    This is a logically centralized directory of services. The registry provides a central place where developers can publish new services or find existing ones. It therefore serves as a centralized clearinghouse for companies and their services.

  2. Web Service Protocol Stack

  A second option for viewing the web service architecture is to examine the emerging web service protocol stack. The stack is still evolving, but currently has four main layers.

  • Service transport
    This layer is responsible for transporting messages between applications. Currently, this layer includes hypertext transfer protocol (HTTP), Simple Mail Transfer Protocol (SMTP), file transfer protocol (FTP), and newer protocols, such as Blocks Extensible Exchange Protocol (BEEP).
  • XML messaging
    This layer is responsible for encoding messages in a common XML format so that messages can be understood at either end. Currently, this layer includes XML-RPC and SOAP.
  • Service description
    This layer is responsible for describing the public interface to a specific web service. Currently, service description is handled via the Web Service Description Language (WSDL).
  • Service discovery
    This layer is responsible for centralizing services into a common registry, and providing easy publish/find functionality. Currently, service discovery is handled via Universal Description, Discovery, and Integration (UDDI).
    As web services evolve, additional layers may be added, and additional technologies may be added to each layer.

  Next chapter explains about various components of Web Services.
  
  

  Few Words about Service Transport

  The bottom of the web service protocol stack is service transport. This layer is responsible for actually transporting XML messages between two computers.
  • Hyper Text Transfer Protocol (HTTP)
    Currently, HTTP is the most popular option for service transport. HTTP is simple, stable, and widely deployed. Furthermore, most firewalls allow HTTP traffic. This allows XMLRPC or SOAP messages to masquerade as HTTP messages. This is good if you want to easily integrate remote applications, but it does raise a number of security concerns.
  • Blocks Extensible Exchange Protocol (BEPP)
    One promising alternative to HTTP is the Blocks Extensible Exchange Protocol (BEEP).BEEP is a new IETF framework of best practices for building new protocols. BEEP is layered directly on TCP and includes a number of built-in features, including an initial handshake protocol, authentication, security, and error handling. Using BEEP, one can create new protocols for a variety of applications, including instant messaging, file transfer, content syndication, and network management
  SOAP is not tied to any specific transport protocol. In fact, you can use SOAP via HTTP, SMTP, or FTP. One promising idea is therefore to use SOAP over BEEP.
  
  

  Web Services Components

  
  

  Over the past few years, three primary technologies have emerged as worldwide standards that make up the core of today's web services technology. These technologies are:

  - XML-RPC

  This is the simplest XML based protocol for exchanging information between computers.

  • XML-RPC is a simple protocol that uses XML messages to perform RPCs.
  • Requests are encoded in XML and sent via HTTP POST.
  • XML responses are embedded in the body of the HTTP response.
  • XML-RPC is platform-independent.
  • XML-RPC allows diverse applications to communicate.
  • A Java client can speak XML-RPC to a Perl server.
  • XML-RPC is the easiest way to get started with web services.
  
  

  - SOAP

  SOAP is an XML-based protocol for exchanging information between computers.
  • SOAP is a communication protocol
  • SOAP is for communication between applications
  • SOAP is a format for sending messages
  • SOAP is designed to communicate via Internet
  • SOAP is platform independent
  • SOAP is language independent
  • SOAP is simple and extensible
  • SOAP allows you to get around firewalls
  • SOAP will be developed as a W3C standard
  SOAP is a simple and open standard XML-based protocol for exchanging information between computers.
  In this tutorial you will learn what is SOAP and Why and How to use it.
  SOAP is very easy to learn and to use and in demand too.
  
  

   WSDL

  WSDL is an XML-based language for describing Web services and how to access them.
  
  • WSDL stands for Web Services Description Language
  • WSDL is an XML based protocol for information exchange in decentralized and distributed environments.
  • WSDL is the standard format for describing a web service.
  • WSDL definition describes how to access a web service and what operations it will perform.
  • WSDL is a language for describing how to interface with XML-based services.
  • WSDL is an integral part of UDDI, an XML-based worldwide business registry.
  • WSDL is the language that UDDI uses.
  • WSDL was developed jointly by Microsoft and IBM.
  • WSDL is pronounced as 'wiz-dull' and spelled out as 'W-S-D-L'
    Web Services Description Language is the standard format for describing a web service in XML format.
    In this tutorial you will learn what is WSDL and Why and How to use it.
    WSDL is very easy to learn and very important for Web Services.

    - UDDI

    UDDI is an XML-based standard for describing, publishing, and finding Web services.
    
    • UDDI stands for Universal Description, Discovery and Integration.
    • UDDI is a specification for a distributed registry of Web services.
    • UDDI is platform independent, open framework.
    • UDDI can communicate via SOAP, CORBA, Java RMI Protocol.
    • UDDI uses WSDL to describe interfaces to web services.
    • UDDI is seen with SOAP and WSDL as one of the three foundation standards of web services.
    • UDDI is an open industry initiative enabling businesses to discover each other and define how they interact over the Internet.
    
    Web Services - Examples
    
    
    
    Based on the Web Service Architecture we will create following two components as a part of Web Services implementation
    • Service provider or publisher:
      This is the provider of the web service. The service provider implements the service and makes it available on the Internet or intranet.
      We will write and publish a simple web Service using .NET SDK.
    • Service requestor or consumer
      This is any consumer of the web service. The requestor utilizes an existing web service by opening a network connection and sending an XML request.
      We will also write two Web Service requestors: one Web-based consumer (ASP.NET application) and another Windows application-based consumer.
    Following is our First Web Service example which works as a service provider and exposes two methods (add and SayHello) as Web Services to be used by applications. This is a standard template for a Web Service. .NET Web Services use the .asmx extension. Note that a method exposed as a Web Service has the WebMethod attribute. Save this file as FirstService.asmx in the IIS virtual directory (as explained in configuring IIS; for example, c:\MyWebSerces).
    
    

    
    using System;
    using System.Linq;
    using System.Web;
    using System.Web.Services;
    using System.Web.Services.Protocols;
    using System.Xml.Linq;
    
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    
    // [System.Web.Script.Services.ScriptService]
    public class Service : System.Web.Services.WebService
    {
        public Service () 
       
    

    {

    
    
    

         //InitializeComponent(); 

    
    
    
    
    
        }
    
        [WebMethod]
        public string MyClass() 
        {
           return "Our WEB_SERVER_ is Prprly RuNNing in Server Side";
        }
        
    }
    

    
    
    
    
    To test a Web Service, it must be published. A Web Service can be published either on an intranet or the Internet. We will publish this Web Service on IIS running on a local machine. Let's start with configuring the IIS.
    • Open Start->Settings->Control Panel->Administrative tools->Internet Services Manager.
    • Expand and right-click on [Default Web Site]; select New ->Virtual Directory.
    • The Virtual Directory Creation Wizard opens. Click Next.
    • The "Virtual Directory Alias" screen opens. Type the virtual directory name—for example, MyWebServices—and click Next.
    • The "Web Site Content Directory" screen opens. Here, enter the directory path name for the virtual directory—for example, c:\MyWebServices—and click Next.
    • The "Access Permission" screen opens. Change the settings as per your requirements. Let's keep the default settings for this exercise. Click the Next button. It completes the IIS configuration. Click Finish to complete the configuration.
    To test that IIS has been configured properly, copy an HTML file (for example, x.html) in the virtual directory (C:\MyWebServices) created above. Now, open Internet Explorer and type http://localhost/MyWebServices/x.html. It should open the x.html file. If it does not work, try replacing localhost with the IP address of your machine. If it still does not work, check whether IIS is running; you may need to reconfigure IIS and Virtual Directory.
    To test our Web Service, copy FirstService.asmx in the IIS virtual directory created above (C:\MyWebServices). Open the Web Service in Internet Explorer (http://localhost/MyWebServices/FirstService.asmx). It should open your Web Service page. The page should have links to two methods exposed as Web Services by our application. Congratulations; you have written your first Web Service!!!

    Testing the Web Service

    As we have just seen, writing Web Services is easy in the .NET Framework. Writing Web Service consumers is also easy in the .NET framework; however, it is a bit more involved. As said earlier, we will write two types of service consumers, one Web- and another Windows application-based consumer. Let's write our first Web Service consumer.

    Web-Based Service Consumer

    Write a Web-based consumer as given below. Call it WebApp.aspx. Note that it is an ASP.NET application. Save this in the virtual directory of the Web Service (c:\MyWebServices\WebApp.axpx).
    This application has two text fields that are used to get numbers from the user to be added. It has one button, Execute, that, when clicked, gets the Add and SayHello Web Services.
    
    
    
    
    After the consumer is created, we need to create a proxy for the Web Service to be consumed. This work is done automatically by Visual Studio .NET for us when referencing a Web Service that has been added. Here are the steps to be followed:
    • Create a proxy for the Web Service to be consumed. The proxy is created using the wsdl utility supplied with the .NET SDK. This utility extracts information from the Web Service and creates a proxy. Thus, the proxy created is valid only for a particular Web Service. If you need to consume other Web Services, you need to create a proxy for this service as well. VS .NET creates a proxy automatically for you when the reference for the Web Service is added. Create a proxy for the Web Service using the wsdl utility supplied with the .NET SDK. It will create FirstSevice.cs in the current directory. We need to compile it to create FirstService.dll (proxy) for the Web Service.

    c:> WSDL http://localhost/MyWebServices/FirstService.asmx?WSDL
    c:> csc /t:library FirstService.cs
    

    • Put the compiled proxy in the bin directory of the virtual directory of the Web Service (c:\MyWebServices\bin). IIS looks for the proxy in this directory.
    • Create the service consumer, which we have already done. Note that I have instantiated an object of the Web Service proxy in the consumer. This proxy takes care of interacting with the service.
    • Type the URL of the consumer in IE to test it (for example, http://localhost/MyWebServices/WebApp.aspx).

    Windows Application-Based Web Service Consumer

    Writing a Windows application-based Web Service consumer is the same as writing any other Windows application. The only work to be done is to create the proxy (which we have already done) and reference this proxy when compiling the application. Following is our Windows application that uses the Web Service. This application creates a Web Service object (of course, proxy) and calls the SayHello and Add methods on it.

    
    
    using System;
    using System.Configuration;
    using System.Data;
    using System.Linq;
    using System.Web;
    using System.Web.Security;
    using System.Web.UI;
    using System.Web.UI.HtmlControls;
    using System.Web.UI.WebControls;
    using System.Web.UI.WebControls.WebParts;
    using System.Xml.Linq;
    
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
    
        }
        protected void Button1_Click(object sender, EventArgs e)
        {
            MYServices.Service ws = new MYServices.Service();
            string s = ws.MyClass();
            Response.Write("<script>alert('" + s.ToString() + "')</script>");
        }
    }
    

    
    

    
    
    

    
    Compile it using c:>csc /r:FirstService.dll WinApp.cs. It will create WinApp.exe. Run it to test the application and the Web Service.
    
    Now, the question arises: How can I be sure that my application is actually calling the Web Service? It is simple to test. Stop your Web server so that the Web Service cannot be contacted. Now, run the WinApp application. It will fire a run-time exception. Now, start the Web server again. It should work.
    
    Web Services Security
    
    Security is critical to web services. However, neither the XML-RPC nor SOAP specifications make any explicit security or authentication requirements.
    
    There are three specific security issues with Web Services:
    
    
    Confidentiality
    
    
    Authentication
    
    
    Network Security
    
    
    
    Confidentiality
    
    If a client sends an XML request to a server, then question is that can we ensure that the communication remains confidential?
    
    Answer lies here
    
    
    XML-RPC and SOAP run primariy on top of HTTP.
    
    
    HTTP has support for Secure Socktes Layer (SSL).
    
    
    Communication can be encrypted via the SSL.
    
    
    SSL is a proven technology and widely deployed.
    
    
    
    But a single web service may consist of a chain of applications. For example one large service might tie together the services of three other applications. In this case, SSL is not adequate; the messages need to be encrypted at each node along the service path, and each node represents a potential weak link in the chain. Currently, there is no agreed-upon solution to this issue, but one promising solution is the W3C XML Encryption Standard. This standard provides a framework for encrypting and decrypting entire XML documents or just portions of an XML document. Check it at http://www.w3.org/Encryption
    
    
    Authentication
    
    If a client connects to a web service, how do we identify the user? And is the user authorized to use the service?
    
    Following options can be considered but there is no clear consensus on a strong authentication scheme.
    
    
    HTTP includes built-in support for Basic and Digest authentication, and services can therefore be protected in much the same manner as HTML documents are currently protected.
    
    
    SOAP Security Extensions: Digital Signature (SOAP-DSIG). DSIG leverages public key cryptography to digitally sign SOAP messages. This enables the client or server to validate the identity of the other party. Check it at http://www.w3.org/TR/SOAP-dsig.
    
    
    The Organization for the Advancement of Structured Information Standards (OASIS) is working on the Security Assertion Markup Language (SAML).
    
    
    
    
    Network Security
    
    There is currently no easy answer to this problem, and it has been the subject of much debate. For now, if you are truly intent on filtering out SOAP or XML-RPC messages, one possibility is to filter out all HTTP POST requests that set their content type to text/xml.
    
    Another alternative is to filter for the SOAPAction HTTP header attribute. Firewall vendors are also currently developing tools explicitly designed to filter web service traffic.