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Chapter: XML and Web Services : Building XML-Based Applications : Web Services Building Blocks: SOAP(Simple Object Access Protocol)

SOAP Implementations

As you have probably gathered by the cautions in this chapter, there are two leading SOAP implementations available today: Microsoft’s SOAP Toolkit (currently at version 2.0 SP2) and Apache SOAP (now at version 2.2), which was originally created by IBM, who donated it to the Apache Foundation.

SOAP Implementations


As you have probably gathered by the cautions in this chapter, there are two leading SOAP implementations available today: Microsoft’s SOAP Toolkit (currently at version 2.0 SP2) and Apache SOAP (now at version 2.2), which was originally created by IBM, who donated it to the Apache Foundation. The Microsoft Toolkit supports all COM-compliant languages—in particular, Visual Basic, and C#. The Apache implementation uses Java.


However, several other SOAP implementations are available, as well. Table 15.3 lists several of the most popular implementations.


TABLE 15.3   Some Popular SOAP Implementations

At this point in time, there are two main issues with the available SOAP implementa-tions: First, how well do they support an overall Web Services implementation? Second, how interoperable they are? The discussion of how well each of the leading SOAP implementations supports Web Services appears in Chapter 16, in the discussion of WSDL and UDDI. The question of interoperability among SOAP implementations is also a critical issue for this nascent technology.


Microsoft SOAP Toolkit


The Microsoft SOAP Toolkit can be found at http://msdn.Microsoft.com/soap. You must have the Visual Basic runtime files and the Windows Installer installed on your sys-tem before you install the toolkit. The toolkit also requires Internet Explorer 5.0, or higher, and will install MSXML 3.0 SP1 (if it isn’t already present). You will also need Visual Basic or another development tool that can compile DLL files, if you will be cre-ating your own.


The SOAP Toolkit contains the following elements:


      A client-side component that enables an application to invoke Web Services opera-tions that are described by a WSDL document.


      A server-side component that maps those operations to COM object method calls. These calls are described by the WSDL and Web Services Meta Language (WSML) files.


      Marshaling and unmarshaling components.


      A WSDL/WSML document-generator tool.


In order to exchange SOAP messages, you must set up the SOAP server and the SOAP client. The server requires a system running Internet Information Services (IIS). To set up the server, you can either choose an Internet Server API (ISAPI) server or an Active Server Pages (ASP) server as the listener. You then create an ActiveX DLL within Microsoft Visual Basic that contains the actual server code (sample code comes with the toolkit). Listing 15.1 shows a sample DLL that calculates a base rate or a replacement cost, which you will need to compile with Visual Basic.

LISTING 15.1  CalcRateBase.vbs—DLL File


Public  Function  CalcBaseRate(ByVal  RawBaseRate  As  Double,


ByVal RelativeFactor As Double, ByVal TerritoryFactor As Double) As Double CalcBaseRate = RawBaseRate * RelativeFactor * TerritoryFactor


End  Function


Public  Function  CalcReplacementCost(ByVal  BaseRate  As  Double,

ByVal  ReplacementCostFactor  As  Double)  As  Double


CalcReplacementCost  =  BaseRate  *  ReplacementCostFactor


End  Function


Public  Function  DisplayVersion()  As  String


DisplayVersion  =  “Version  1.0”


End  Function


Run the SOAP Toolkit Wizard and name your service with the toolkit. Then select the COM DLL file to analyze, as shown in Figure 15.2.

Then select the services you would like to expose, as shown in Figure 15.3.


Next, create a virtual root using IIS and then create the WSDL file and the WSML files that describe the Web Service. (More about WSDL and WSML in Chapter 16.)

LISTING 15.2  RateCalcSvc.wsdl—Generated WSDL File


<?xml  version=’1.0’  encoding=’UTF-16’  ?>


<!— Generated 09/24/01 by Microsoft SOAP Toolkit WSDL File Generator, Version 1.02.813.0 —>


<definitions name =’RateCalcSvc’ targetNamespace = ‘http://tempuri.org/wsdl/’ xmlns:wsdlns=’http://tempuri.org/wsdl/’ xmlns:typens=’http://tempuri.org/type’ xmlns:soap=’http://schemas.xmlsoap.org/wsdl/soap/’ xmlns:xsd=’http://www.w3.org/2001/XMLSchema’ xmlns:stk=’http://schemas.microsoft.com/soap-toolkit/wsdl-extension’ xmlns=’http://schemas.xmlsoap.org/wsdl/’>




<schema targetNamespace=’http://tempuri.org/type’ xmlns=’http://www.w3.org/2001/XMLSchema’ xmlns:SOAP-ENC=’http://schemas.xmlsoap.org/soap/encoding/’ xmlns:wsdl=’http://schemas.xmlsoap.org/wsdl/’ elementFormDefault=’qualified’>






<message  name=’Class1.CalcBaseRate’>


<part name=’RawBaseRate’ type=’xsd:float’/> <part name=’RelativeFactor’ type=’xsd:float’/> <part name=’TerritoryFactor’ type=’xsd:float’/>




<message name=’Class1.CalcBaseRateResponse’> <part name=’Result’ type=’xsd:float’/>




<message name=’Class1.CalcReplacementCost’> <part name=’BaseRate’ type=’xsd:float’/>


<part  name=’ReplacementCostFactor’  type=’xsd:float’/>



<message name=’Class1.CalcReplacementCostResponse’> <part name=’Result’ type=’xsd:float’/>




<message name=’Class1.DisplayVersion’> </message>


<message name=’Class1.DisplayVersionResponse’> <part name=’Result’ type=’xsd:string’/>




<portType name=’Class1SoapPort’> <operation name=’CalcBaseRate’


parameterOrder=’RawBaseRate RelativeFactor TerritoryFactor’> <input message=’wsdlns:Class1.CalcBaseRate’ />


<output message=’wsdlns:Class1.CalcBaseRateResponse’ /> </operation>


<operation name=’CalcReplacementCost’ parameterOrder=’BaseRate ReplacementCostFactor’>


<input  message=’wsdlns:Class1.CalcReplacementCost’  />


<output message=’wsdlns:Class1.CalcReplacementCostResponse’ /> </operation>


<operation name=’DisplayVersion’ parameterOrder=’’> <input message=’wsdlns:Class1.DisplayVersion’ />


<output message=’wsdlns:Class1.DisplayVersionResponse’ /> </operation>




<binding name=’Class1SoapBinding’ type=’wsdlns:Class1SoapPort’ > <stk:binding preferredEncoding=’UTF-16’/>




style=’rpc’ transport=’http://schemas.xmlsoap.org/soap/http’ /> <operation name=’CalcBaseRate’ >


<soap:operation soapAction=’http://tempuri.org/action/Class1.CalcBaseRate’ />




<soap:body use=’encoded’ namespace=’http://tempuri.org/message/’ encodingStyle=’http://schemas.xmlsoap.org/soap/encoding/’ />






<soap:body use=’encoded’ namespace=’http://tempuri.org/message/’ encodingStyle=’http://schemas.xmlsoap.org/soap/encoding/’ />






<operation name=’CalcReplacementCost’ > <soap:operation


soapAction=’http://tempuri.org/action/Class1.CalcReplacementCost’ /> <input>


<soap:body use=’encoded’ namespace=’http://tempuri.org/message/’ encodingStyle=’http://schemas.xmlsoap.org/soap/encoding/’ />






<soap:body use=’encoded’ namespace=’http://tempuri.org/message/’ encodingStyle=’http://schemas.xmlsoap.org/soap/encoding/’ />






<operation name=’DisplayVersion’ > <soap:operation


soapAction=’http://tempuri.org/action/Class1.DisplayVersion’  />




<soap:body use=’encoded’ namespace=’http://tempuri.org/message/’ encodingStyle=’http://schemas.xmlsoap.org/soap/encoding/’ />






<soap:body use=’encoded’ namespace=’http://tempuri.org/message/’ encodingStyle=’http://schemas.xmlsoap.org/soap/encoding/’ />








<service  name=’RateCalcSvc’  >


<port name=’Class1SoapPort’ binding=’wsdlns:Class1SoapBinding’ > <soap: address location=’’ />








And Listing 15.3 shows the corresponding WSML.


LISTING 15.3  RateCalcSvc.wsml—Generated WSML File


<?xml  version=’1.0’  encoding=’UTF-16’  ?>


<!— Generated 09/24/01 by Microsoft SOAP Toolkit WSDL File Generator, Version 1.02.813.0 —>


<servicemapping name=’RateCalcSvc’> <service name=’RateCalcSvc’>


<using PROGID=’Project1.Class1’ cachable=’0’ ID=’Class1Object’ /> <port name=’Class1SoapPort’>


<operation  name=’CalcBaseRate’>


<execute uses=’Class1Object’ method=’CalcBaseRate’ dispID=’1610809344’>


<parameter callIndex=’1’ name=’RawBaseRate’ elementName=’RawBaseRate’ />


<parameter callIndex=’2’ name=’RelativeFactor’ elementName=’RelativeFactor’ />


<parameter callIndex=’3’ name=’TerritoryFactor’ elementName=’TerritoryFactor’ />


<parameter callIndex=’-1’ name=’retval’ elementName=’Result’ /> </execute>




<operation  name=’CalcReplacementCost’>


<execute uses=’Class1Object’ method=’CalcReplacementCost’ dispID=’1610809345’>


<parameter callIndex=’1’ name=’BaseRate’ elementName=’BaseRate’ /> <parameter callIndex=’2’ name=’ReplacementCostFactor’


elementName=’ReplacementCostFactor’  />


<parameter callIndex=’-1’ name=’retval’ elementName=’Result’ /> </execute>




<operation name=’DisplayVersion’> <execute uses=’Class1Object’


method=’DisplayVersion’  dispID=’1610809346’>


<parameter callIndex=’-1’ name=’retval’ elementName=’Result’ /> </execute>










Finally, create an ASP application to handle incoming SOAP requests.


To set up the client, write a Visual Basic Scripting Edition (VBScript) application that calls the operations that your server provides. Listing 15.4 shows our sample client.


LISTING 15.4  SoapClient.vbs—Sample SOAP Client


Option  Explicit


Dim soapClient,BaseRate, RelativityFactor, TerritoryFactor, AdjustedBase, ReplaceCost, ReplaceCostFactor, TotalCost


set soapclient = CreateObject(“MSSOAP.SoapClient”) On Error Resume Next


Call soapclient.mssoapinit(“http://mysite.com/rates/RateCalcSvc.wsdl”, “RateCalcSvc”, “Class1SoapPort”)


if  err  <>  0  then


wscript.echo “Initialization Failed “ + err.description else


wscript.echo “Initialization Successful “ end if


wscript.echo “” wscript.echo “”


BaseRate  =  303


RelativityFactor  =  .97


TerritoryFactor  =  1.2


ReplaceCostFactor  =  .21


AdjustedBase  =  0

Apache SOAP


You can find the open-source Apache SOAP 2.2 at http://xml.apache.org/soap. You will need to have the following tools installed on your system before you install Apache SOAP:


   Java 1.1 or higher.


   Apache Jakarta Tomcat 3.2.1 Web server and servlet engine, available at




   Apache Xerxes XML Parser 1.2.3, found at  http://xml.apache.org/xerces-j/


   JavaMail (mail.jar), found at http://java.sun.com/products/javamail/, and


the JavaBeans Activation Framework (activation.jar), found at




Once all the tools (including Apache SOAP) are installed and your CLASSPATH is cor-rectly updated, you must configure Tomcat so that it can detect Apache SOAP. Edit the file \jakarta-tomcat-3.2\conf\server.xml and put the following entry near the end of the file:


<Context path=”/soap” docBase=”C:/soap-2_0/webapps/soap” reloadable=”true”> </Context>


Next, launch Tomcat. You should see the output:


Starting  tomcat.  Check  logs/tomcat.log  for  error  messages


Now, point your browser to http://localhost/soap (including the port number, if you have chosen a port other than 80) to launch the Apache SOAP system.


Next, we need to write a Web Service in Java. Listing 15.5 shows a sample service that calculates a rate (in this case, returning the same value every time).

LISTING 15.5  Exchange.java—Sample Web Service


public  class  Exchange




public  float  getRate(  String  BaseRate,  String  ReplacementCostFactor  )




System.out.println( “getRate( “ + BaseRate + “, “ + ReplacementCostFactor + “ )” );


return  1234.56F;






Put the directory that contains the Exchange class on your CLASSPATH and compile it. Restart Tomcat and run the admin client from your browser. From the admin client, click Deploy, and you’ll see the screen shown in Figure 15.5.

Enter the necessary information, as shown in Figure 15.5, and click the Deploy button again. If you have successfully deployed your Web Service, you should see the screen shown in Figure 15.6.

Next, we must run our client application. Listing 15.6 shows a simple example of a Java client.


LISTING 15.6  Client.java—Sample SOAP Client


import java.net.*; import java.util.*; import org.apache.soap.*;


import org.apache.soap.rpc.*; public class Client




public  static  void  main(  String[]  args  )  throws  Exception




URL url = new URL( “http://localhost/soap/servlet/rpcrouter” ); String urn = “urn:demo1:exchange”;


Call call = new Call(); // prepare to invoke the Service call.setTargetObjectURI( urn );


call.setMethodName(  “getRate”  );


call.setEncodingStyleURI( Constants.NS_URI_SOAP_ENC ); // the default Vector v = new Vector();


v.addElement( new Parameter( “BaseRate”, String.class, “12.34”, null ) ); v.addElement( new Parameter( “ReplacementCostFactor”, String.class,


”56.78”, null ) ); call.setParams( v ); try




System.out.println( “Service invoked:\n” + “ URL= “ + url + “\n URN= “ + urn );


Response response = call.invoke( url, “” ); // invoke the Service

if( !response.generatedFault() )




Parameter r = response.getReturnValue(); // response was OK

System.out.println( “Result= “ + r.getValue() );






Fault f = response.getFault(); // error

System.err.println( “Fault= “ + f.getFaultCode() + “, “ +


f.getFaultString()  );






catch(  SOAPException  e  )  //  error  sending  call




System.err.println( “SOAPException= “ + e.getFaultCode() + “, “ + e.getMessage() );








Compile and run the client, and you should see the following output:


Service  invoked:

URL=  http://localhost/soap/servlet/rpcrouter


URN=  urn:demo1:exchange


Result=  1234.56


Finally, the output from the Tomcat server should include the following:


Processing  SOAP  request...


GetRate  (12.34,  56.78  )


We have successfully invoked our Web Service!


Interoperability Issues


Interoperability among different SOAP implementations is especially important, because, well, interoperability is what Web Services are all about. What’s the point of having loosely coupled services if they can only talk to systems that use the same implementa-tion? The fact that interoperability is an issue at all is a symptom of the fact that Web Services are still on the bleeding edge. This issue is currently a topic of much discussion, and there is a good chance that the issue will be resolved in 2002.


The fundamental cause of most interoperability problems has to do with a single word: may. When the SOAP specification says that a particular feature may be implemented, it opens up the option that a particular vendor may choose not to implement the feature. Another implementation, however, may use the feature, causing the two implementations to be incompatible with each other.


Interoperability issues with SOAP implementations fall into three general categories:


   Transport problems, namely those involving the HTTP SOAPAction header.


   XML issues, typically involving the Byte Order Mark.


   SOAP problems, involving the mustUnderstand attribute or other unevenly imple-mented features of the specification.


Let’s look at each of these issues in turn.


First, as discussed earlier, the SOAPAction header is mandatory in SOAP messages that go over HTTP. However, the SOAP specification allows for a null SOAPAction, which appears like this:




However, Apache SOAP does not have any way of interpreting a null header value, caus-ing messages that have null values to be incompatible with those SOAP messages that have this header.


Second, there is the issue of the Byte Order Mark (BOM). A BOM is a nonprintable character that indicates the order of the bytes in a two-byte character encoding (like those for Japanese and Chinese). BOMs are required for two-byte encodings such as UTF-16, but they serve little purpose (even though they are not forbidden) for single-byte encod-ings such as UTF-8. Apache SOAP, for example, cannot interpret UTF-8-encoded SOAP messages that have a BOM, even though many text editors (such as Notepad) automati-cally place a BOM at the beginning of UTF-8-encoded text.


Finally, the third category of incompatibility issues has to do with inconsistent imple-mentations of SOAP. Table 15.4 contains a reasonably comprehensive accounting of the current state of SOAP feature support in the three leading SOAP implementations.


TABLE 15.4    SOAP Compatibility Matrix

Whenever a SOAP feature is not fully supported across different implementations, there is always the possibility of a failure to exchange SOAP messages correctly. The fact that relatively few rows in Table 15.4 contain only “Yes” is a clear indication of the immatu-rity of the SOAP protocol.

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