Professional ASP.NET 3.5 in C# and Visual Basic Part 140 pdf

Consuming a Web Service Using SOAP Headers It really is not difficult to build an ASP.NET application that makes a SOAP request to a Web service using SOAP headers.. Just as with the Web

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In this example, theSoapHeaderattribute takes astringvalue of the name of the instantiatedSoapHeader

class — in this case,myHeader

From here, theWebMethodactually makes use of themyHeaderobject If themyHeaderobject is not found (meaning that the client did not send in a SOAP header with his constructed SOAP message), a simple

‘‘Hello World’’ is returned However, if values are provided in the SOAP header of the SOAP request,

those values are used within the returnedstringvalue

Consuming a Web Service Using SOAP Headers

It really is not difficult to build an ASP.NET application that makes a SOAP request to a Web service

using SOAP headers Just as with the Web services that do not include SOAP headers, you make a Web Reference to the remote Web service directly in Visual Studio

For the ASP.NET page, create a simple page with a single Label control The output of the Web service is placed in the Label control The code for the ASP.NET page is shown in Listing 29-19

Listing 29-19: An ASP.NET page working with an XML Web service using SOAP headers

VB

<%@ Page Language="VB" %>

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)

Dim ws As New localhost.HelloSoapHeader() Dim wsHeader As New localhost.HelloHeader() wsHeader.Username = "Bill Evjen"

wsHeader.Password = "Bubbles"

ws.HelloHeaderValue = wsHeader Label1.Text = ws.HelloWorld() End Sub

</script>

<title>Working with SOAP headers</title>

</head>

<body>

<div>

<asp:Label ID="Label1" Runat="server"></asp:Label>

</div>

</form>

</body>

</html>

C#

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

Continued

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protected void Page_Load(object sender, System.EventArgs e) {

localhost.HelloSoapHeader ws = new localhost.HelloSoapHeader();

localhost.HelloHeader wsHeader = new localhost.HelloHeader();

wsHeader.Username = "Bill Evjen";

wsHeader.Password = "Bubbles";

ws.HelloHeaderValue = wsHeader;

Label1.Text = ws.HelloWorld();

}

</script>

Two objects are instantiated The first is the actual Web service,HelloSoapHeader The second, which

is instantiated aswsHeader, is theSoapHeaderobject After both of these objects are instantiated and

before making the SOAP request in the application, you construct the SOAP header This is as easy as

assigning values to theUsernameandPasswordproperties of thewsHeaderobject After these properties

are assigned, you associate thewsHeaderobject to thewsobject through the use of theHelloHeaderValue

property After you have made the association between the constructed SOAP header object and the

actualWebMethodobject (ws), you can make a SOAP request just as you would normally do:

Label1.Text = ws.HelloWorld()

Running the page produces the result in the browser shown in Figure 29-16

Figure 29-16

What is more interesting, however, is that the SOAP request reveals that the SOAP header was indeed

constructed into the overall SOAP message, as shown in Listing 29-20

Listing 29-20: The SOAP request

<?xml version="1.0" encoding="utf-8" ?>

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:xsd="http://www.w3.org/2001/XMLSchema">

<soap:Header>

<Username>Bill Evjen</Username>

<Password>Bubbles</Password>

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</soap:Header>

<soap:Body>

</soap:Body>

</soap:Envelope>

This returns the SOAP response shown in Listing 29-21

Listing 29-21: The SOAP response

<?xml version="1.0" encoding="utf-8" ?>

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"

<soap:Body>

<HelloWorldResult>Hello Bill Evjen Your password is:

Bubbles</HelloWorldResult>

</HelloWorldResponse>

</soap:Body>

</soap:Envelope>

Requesting Web Services Using SOAP 1.2

Most Web services out there use SOAP version 1.1 for the construction of their messages With that

said, SOAP 1.2 became a W3 C recommendation in June 2003 (seewww.w3.org/TR/soap12-part1/)

The nice thing about XML Web services in the NET Framework platform is that they are capable of

communicating in both the 1.1 and 1.2 versions of SOAP

In an ASP.NET application that is consuming a Web service, you can control whether the SOAP request

is constructed as a SOAP 1.1 message or a 1.2 message Listing 29-22 changes the previous example so

that the request uses SOAP 1.2 instead of the default setting of SOAP 1.1

Listing 29-22: An ASP.NET application making a SOAP request using SOAP 1.2

VB

Dim ws As New localhost.HelloSoapHeader() Dim wsHeader As New localhost.HelloHeader() wsHeader.Username = "Bill Evjen"

wsHeader.Password = "Bubbles"

ws.HelloHeaderValue = wsHeader ws.SoapVersion = System.Web.Services.Protocols.SoapProtocolVersion.Soap12 Label1.Text = ws.HelloWorld()

Continued

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End Sub

</script>

C#

localhost.HelloSoapHeader ws = new localhost.HelloSoapHeader();

localhost.HelloHeader wsHeader = new localhost.HelloHeader();

wsHeader.Username = "Bill Evjen";

wsHeader.Password = "Bubbles";

ws.HelloHeaderValue = wsHeader;

ws.SoapVersion = System.Web.Services.Protocols.SoapProtocolVersion.Soap12;

Label1.Text = ws.HelloWorld();

}

</script>

In this example, you first provide an instantiation of the Web service object and use the new

SoapVer-sionproperty The property takes a value ofSystem.Web.Services.Protocols.SoapProtocolVersion

.Soap12to work with SOAP 1.2 specifically

With this bit of code in place, the SOAP request takes the structure shown in Listing 29-23

Listing 29-23: The SOAP request using SOAP 1.2

<?xml version="1.0" encoding="utf-8"?>

<soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope"

<soap:Header>

<Username>Bill Evjen</Username>

<Password>Bubbles</Password>

</HelloHeader>

</soap:Header>

<soap:Body>

</soap:Body>

</soap:Envelope>

One difference between the two examples is thexmlns:soapnamespace that is used The difference

actu-ally resides in the HTTP header When you compare the SOAP 1.1 and 1.2 messages, you see a difference

in theContent-Typeattribute In addition, the SOAP 1.2 HTTP header does not use thesoapaction

attribute because this is now combined with theContent-Typeattribute

You can turn off either SOAP 1.1 or 1.2 capabilities with the Web services that you build by making the

proper settings in theweb.configfile, as shown in Listing 29-24

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Listing 29-24: Turning off SOAP 1.1 or 1.2 capabilities

<system.web>

</protocols>

</webServices>

</system.web>

</configuration>

Consuming Web Ser vices Asynchronously

All the Web services that you have been working with in this chapter have been done synchronously This

means that after a request is sent from the code of an ASP.NET application, the application comes to a

complete standstill until a SOAP response is received

The process of invoking aWebMethodand getting back a result can take some time for certain requests At times, you are not in control of the Web service from which you are requesting data and, therefore, you are not in control of the performance or response times of these services For these reasons, you should

consider consuming Web services asynchronously.

An ASP.NET application that makes an asynchronous request can work on other programming tasks

while the initial SOAP request is awaiting a response When the ASP.NET application is done working

on the additional items, it can return to get the result form the Web service

The great news is that to build an XML Web service that allows asynchronous communication, you

don’t have to perform any additional actions All.asmxWeb services have the built-in capability for

asynchronous communication with consumers The Web service in Listing 29-25 is an example

Listing 29-25: A slow Web service

VB

Imports System.Web

Imports System.Web.Services

Imports System.Web.Services.Protocols

<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1,

EmitConformanceClaims:=True)> _

Public Class Async

Inherits System.Web.Services.WebService

<WebMethod()> _

Public Function HelloWorld() As String

System.Threading.Thread.Sleep(1000)

Return "Hello World"

Continued

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End Function

End Class

C#

using System;

using System.Web;

using System.Web.Services;

using System.Web.Services.Protocols;

[WebService(Namespace = "http://www.wrox.com/AsyncHelloWorld")]

[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

public class Async : System.Web.Services.WebService

{

[WebMethod]

public string HelloWorld() {

System.Threading.Thread.Sleep(1000);

return "Hello World";

}

This Web service returns a simpleHello Worldas a string, but before it does, the Web service makes a

1000-millisecond pause This is done by putting the Web service thread to sleep using theSleepmethod

Next, take a look at how an ASP.NET application can consume this slow Web service asynchronously, as

illustrated in Listing 29-26

Listing 29-26: An ASP.NET application consuming a Web service asynchronously

VB

Dim ws As New localhost.Async() Dim myIar As IAsyncResult myIar = ws.BeginHelloWorld(Nothing, Nothing) Dim x As Integer = 0

Do Until myIar.IsCompleted = True

x += 1 Loop Label1.Text = "Result from Web service: " & ws.EndHelloWorld(myIar) & _

"<br>Local count while waiting: " & x.ToString() End Sub

</script>

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<title>Async consumption</title>

</head>

<body>

<div>

<asp:Label ID="Label1" Runat="server"></asp:Label>

</div>

</form>

</body>

</html>

C#

localhost.Async ws = new localhost.Async();

IAsyncResult myIar;

myIar = ws.BeginHelloWorld(null, null);

int x = 0;

while (myIar.IsCompleted == false) {

x += 1;

}

Label1.Text = "Result from Web service: " + ws.EndHelloWorld(myIar) +

"<br>Local count while waiting: " + x.ToString();

}

</script>

When you make the Web reference to the remote Web service in the consuming ASP.NET application,

you not only see theHelloWorld WebMethodavailable to you in IntelliSense, you also see a

BeginHel-loWorldand anEndHelloWorld To work with the Web service asynchronously, you must utilize the

BeginHelloWorldandEndHelloWorldmethods

Use theBeginHelloWorldmethod to send a SOAP request to the Web service, but instead of the ASP.NET application waiting idly for a response, it moves on to accomplish other tasks In this case, it is not doing anything that important — just counting the amount of time it is taking in a loop

After the SOAP request is sent from the ASP.NET application, you can use theIAsyncResultobject

to check whether a SOAP response is waiting This is done by usingmyIar.IsCompleted If the

asyn-chronous invocation is not complete, the ASP.NET application increases the value ofxby one before

making the same check again The ASP.NET application continues to do this until the XML Web service

is ready to return a response The response is retrieved using theEndHelloWorldmethod call

Results of running this application are similar to what is shown in Figure 29-17

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Figure 29-17

Windows Communication Foundation

Since the introduction of the NET Framework 3.0, Microsoft has made available a new way to build Web

services beyond the ASP.NET-based Web services presented in this chapter

Until the NET Framework 3.0 came out, it was not a simple task to build components that were required

to communicate a message from one point to another because Microsoft offered more than one

technol-ogy that you could use for such an action

For instance, you could have used ASP.NET Web services (as just seen), Web Service Enhancements

3.0 (WSE), MSMQ, Enterprise Services, NET Remoting, and even theSystem.Messagingnamespace

Each technology has its own pros and cons ASP.NET Web Services (also known as ASMX Web Services)

provided the capability to easily build interoperable Web services The WSE enabled you to easily build

services that took advantage of some of the WS-* message protocols MSMQ enabled the queuing of

messages, making it easy to work with solutions that were only intermittently connected Enterprise

Services, provided as a successor to COM+, offered an easy means to build distributed applications

.NET Remoting was a fast way to move messages from one NET application to another Moreover, these

are Microsoft options only This does not include all the options available in other environments, such as

the Java world

With so many options available to a Microsoft developer, it can be tough to decide which path to

take with the applications you are trying to build With this in mind, Microsoft has created the Windows

Communication Foundation (WCF)

WCF is a new framework for building service-oriented applications Microsoft wanted to provide its

developers with a framework to quickly get a proper service-oriented architecture up and running Using

the WCF, you will be able to take advantage of all the items that make distribution technologies powerful

WCF is the answer and the successor to all these other message distribution

technologies

The Larger Move to SOA

Upon examining WCF, you will find that it is part of a larger movement that organizations are making

toward the much talked about service-oriented architecture, or SOA An SOA is a message-based service

architecture that is vendor agnostic As a result, you have the capability to distribute messages across

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a system, and the messages are interoperable with other systems that would otherwise be considered

incompatible with the provider system

Looking back, you can see the gradual progression to the service-oriented architecture model In the

1980s, the revolution arrived with the concept of everything being an object When object-oriented pro-gramming came on the scene, it was enthusiastically accepted as the proper means to represent entities within a programming model The 1990s took that one step further, and the component-oriented model was born This enabled objects to be encapsulated in a tightly coupled manner It was only recently that the industry turned to a service-oriented architecture because developers and architects needed to take components and have them distributed to other points in an organization, to their partners, or to their

customers This distribution system needed to have the means to transfer messages between machines

that were generally incompatible with one another In addition, the messages had to include the ability

to express the metadata about how a system should handle a message

If you ask 10 people what an SOA is, you’ll probably get 11 different answers, but there are some common principles that are considered to be foundations of a service-oriented architecture:

❑ Boundaries are explicit:Any datastore, logic, or entity uses an interface to expose its data or

capabilities The interface provides the means to hide the behaviors within the service, and the

interface front-end enables you to change this behavior as required without affecting

down-stream consumers

❑ Services are autonomous:All the services are updated or versioned independently of one

another Thus, you do not upgrade a system in its entirety; instead, each component of these

systems is an individual entity within itself and can move forward without waiting for other

components to progress forward Note that with this type of model, once you publish an

inter-face, that interface must remain unchanged Interface changes require new interfaces (versioned,

of course)

❑ Services are based upon contracts, schemas, and policies:All services developed require a con-tract regarding what is required to consume items from the interface (usually done through a

WSDL document) Along with a contract, schemas are required to define the items passed in

as parameters or delivered through the service (using XSD schemas) Finally, policies define any capabilities or requirements of the service

❑ Service compatibility that is based upon policy:The final principle enables services to define

policies (decided at runtime) that are required to consume the service These policies are usually expressed through WS-Policy

If your own organization is considering establishing an SOA, the WCF is a framework that works on

these principles and makes it relatively simple to implement The next section looks at what the WCF

offers Then you can dive into building your first WCF service

WCF Overview

As stated, the Windows Communication Foundation is a means to build distributed applications in a

Microsoft environment Although the distributed application is built upon that environment, this does

not mean that consumers are required to be Microsoft clients or to take any Microsoft component or

technology to accomplish the task of consumption On the other hand, building WCF services means you are also building services that abide by the principles set forth in the aforementioned SOA discussion

and that these services are vendor agnostic — thus, they are able to be consumed by almost anyone

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You can build WCF services using Visual Studio 2008 Note that because this is a NET Framework

3.0 component, you are actually limited to the operating systems in which you can run a WCF service

Whereas the other Microsoft distribution technologies mentioned in this chapter do not have too many

limitations on running on Microsoft operating systems, an application built with WCF can only run on

Windows XP SP2, Windows Vista, or Windows Server 2008

Building a WCF Service

Building a WCF service is not hard to accomplish If you are working from a NET Framework 2.0

envi-ronment, you need to install the NET Framework 3.0 If you have installed the NET Framework 3.5,

then you will find that both the NET Framework 2.0 and 3.0 have been installed also

From there, it is easy to build WCF services directly in Visual Studio 2008 because it is already geared

to work with this application type If you are working with Visual Studio 2005, you need to install the

Visual Studio 2005 extensions for NET Framework 3.0 (WCF and WPF) Download these Visual Studio

extensions, if you are using Visual Studio 2005 Installing the extensions into Visual Studio 2005 adds a

WCF project to your IDE If you are using Visual Studio 2008, the view of the project from the New Web

Site dialog box is presented in Figure 29-18

Figure 29-18

When you build a WCF project in this manner, the idea is that you build a traditional class library that is

compiled down to a DLL that can then be added to another project The separation of code and project

is a powerful division on larger projects That said, you can, however, just as easily build a WCF service

directly in your NET project, whether that is a console application or a Windows Forms application The

approach taken for the examples in this chapter show you how to build a WCF service that is hosted

in a console application Keep in mind that for the services you actually build and deploy, it is usually

better to build them directly as a WCF Service Library project and use the created DLL in your projects or

in IIS itself

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