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TECHNIQUESWRITTEN BYDOUG PORTERWorking with Web Servicesin PowerBuilderAn introductionAUTHOR BIODoug Porter is a softwaredeveloper withDailyAccess Corporation.He is a Sun CertifiedJava Programmerand Certified Power-Builder Professional andwas a speaker at Tech-Wave 2004. He holds aBA in Spanish and anMS in CIS from the Universityof South Alabamawhere he has alsoworked as an adjunctinstructor. Doug worksextensively withEAServer, PowerBuilder,and Java developingclient/server and Webapplications for thefinancial industry.Unless you have been hiding ina cave for the past couple ofyears, you are probably wellaware of the buzz surroundingservice-oriented architecture(SOA). This concept of interactionamong loosely coupled collections ofcomponents is often implementedthrough a series of services accessibleover HTTP that processes requests andresponses (Web services). As a Power-Builder developer you may be wonderinghow you can join the SOA partywhile still leveraging your existingskills. This article will walk youthrough three techniques available tothe PowerBuilder developer (even ifyou may not be on a currently supportedversion).Accessing a Web service is very similarto visiting a Web page containingparameters in the URL or submitting aform on a Web page. An HTTP requestgets sent to a URL via an HTTP GET orPOST along with a set of arguments inthe form of name/value pairs. In Power-Builder there are three options availablefor performing this type of operation:the GetURL/PostURL functions, usingMicrosoft’s XmlHttp object via OLE, andusing the Web Service Proxy object.FIGURE 1 | FIGURE 2 |Demonstration Application toCall Amazon.com Web ServicesIn this article we will create a demonstrationapplication that interacts withthe Amazon.com E-Commerce WebService (http://aws.amazon.com). Ourapplication will use this service tosearch through one of their productindexes for items matching our searchcriteria. To use the Amazon.com Webservice you will need to sign up for anaccess key through their site. The codesamples will show where your keyshould be placed with the indicator“[YourAccessKey]”.By looking at the documentation forthe Amazon E-commerce Web service,we can see that to perform an itemsearch operation a minimal set of argumentsis required. There are many additionalarguments that may be used whenperforming searches, but we will beusing the subset listed below. (Browsethe Amazon.com Web service documentationto see the full range of searcharguments and operations available.)• Web Service URL: http://webservices.amazon.com/onca/xml• Service: Name of the service beingused; should be AWSECommerceService• AWSAccessKeyID: [YourAccessKey]• Operation: Operation to be performed(ItemSearch in our case)• Keywords: Word or phrase to searchfor• SearchIndex: One of Amazon.com’ssearch indexes (Music, Books, etc.)Responses from this Amazon Webservice will be returned as structuredXML that can then be parsed and displayed.A demonstration of the variousmethods available for parsing XML inPowerBuilder will be covered in a laterarticle.Before we can send requests, wemust decide what to search for. I’m ahuge music fan, so for this example wewill use the “Music” SearchIndex andfor our Keywords argument we willsearch for information on one of myfavorite musicians, the great “ButchWalker” (an Atlanta musician formerlywith the Marvelous 3).GetURL/PostURLThe oldest methods for pulling dataover HTTP in PowerBuilder (since version6.5) are the GetURL and PostURLfunctions. These functions allow you tosend an HTTP GET or POST request30 PBDJ volume12 issue11pbdj.sys-con.com
from within PowerScript and capturethe resulting response.When passing arguments to a URLvia an HTTP GET, the URL is generatedin the format:BaseURL?=&=&...The full URL for an HTTP GET to ourAmazon Web services with our selectedparameters would be as follows:http://webservices.amazon.com/onca/xml?Service=AWSECommerceService&AWSAccessKeyID=[YourAccessKey]&Operation=ItemSearch&SearchIndex=Music&Keywords=Butch WalkerThe resulting response would beXML containing a list of items matchingour search (see Figure 1).Now that we know what our requestshould look like, we can begin to writecode to call the Web service. Both theGetURL and PostURL functionsrequire that you first create a standardclass of the type InternetResult to captureand process the Web serviceresponse via the InternetData(blob)function. Once we have created thisclass, we will override the InternetData(blob)function with code to processthe response. For demonstration purposes,a simple MessageBox will do fornow, but we could write the data out toa file or parse it for display in aSOAP vs RESTSOAP: A well-defined protocol forexchanging XML-based messages over anetwork usually via HTTP. Oftentimes it’sused in an RPC (Remote Procedure Call)messaging pattern.REST: In the context of Web services,describes loosely structured requests overHTTP with no set standard defining thestructure of requests or responses fromthe service.DifferencesAccessing a REST-style Web serviceinvolves passing multiple arguments inthe form of name/value pairs via a GETor POST request. These arguments provideall of the incoming parameters theWeb service may need to create aresponse (which may or may not beXML). In contrast, a SOAP-style Web serviceaccepts a single incoming argumentthat consists of well-formed XML. ThisXML argument holds all of the necessaryparameters the Web services requires tocreate a response (which is then returnedas well-formed XML).pbdj.sys-con.comGetURL/PostURL MS XmlHttp Web Service ProxyMinimum PB Version 6.5 6.5 9Supports HTTPS No Yes YesREST Requests Yes Yes NoSOAP Requests Yes Yes YesXML Parsing Standard String MS XmlDom PBDom orParsing object DataWindowManually Create Request Yes Yes NoTABLE 1 |DataWindow. The following code snippetshould be added to the functionInternetData(blob) in the InternetResultobject:MessageBox(“Response”, &String(data))Return 1The code in Listing 1 demonstrates acall to the service with GetURL (seeListing 1). Note that to call theGetURL/PostURL functions, you mustuse GetContextService to get a servicereference to the Internet service.Executing the snippet should generatea MessageBox filled with our XMLresponse from the Amazon Web service.Performing the same operation with aPostURL is almost identical; we just haveto set a couple of extra parameters (contentheaders and port) (see Listing 2).While this approach works well forstandard HTTP requests, theGetURL/PostURL functions do notallow communication over HTTPS. Toachieve secure communication with theWeb service, we must move on to one ofour other two methods.Microsoft XmlHttp ObjectUsing OLEUsing PowerBuilder’s OLE capabilities,we can take advantage ofMicrosoft’s XmlHttp object to sendrequests to a Web service. The code touse this object is very similar to whatwe have seen for GetURL/PostURL. TheXmlHttp object can send requests viaHTTP GET and POST but adds the benefitof being able to also send requestsover HTTPS. Before you may use thisobject, you must download and installthe MSXML package from Microsoft’sWeb site (this example uses version 4.0of the package). One nice added bonusincluded with this package is an XMLparser (handy if you don’t happen to beon a version of PowerBuilder that canparse XML) (see Listing 3).Web Service Proxy ObjectLast but not least is the Web ServiceProxy Object. This object is available tothose who are using PowerBuilder version9 and above. This object examinesa Web service’s WSDL (Web ServiceDescription Language) file to determineall of the services available that may berequested. We will step through the WebService Proxy Wizard to create a proxyobject for our Amazon Web Service. Wecan then deploy this object, which willgenerate a set of objects, methods, andstructures we can use to call our Webservice and capture the response(because of recent changes in the AmazonWSDL file, PowerBuilder 9.0.3 Build8565 or above is required to generate aproxy using the wizard). The Web ServiceProxy uses SOAP-style requests tointeract with our Web service. The othertwo methods shown used REST-stylerequests (for more information see thesidebar SOAP vs REST).To create a Web Service Proxy Object,proceed through the following steps:1. Click New object and select the WebService Proxy Wizard from the Projecttab (see Figure 2).2. Click Next and select a WSDL File.Enter the URL to the Amazon WSDLfile: http://webservices.amazon.com/AWSECommerceService/2005-10-05/AWSECommerceService.wsdl.3. Click Next and select the available servicesexposed through the WSDL file.4. Click Next and select an availableport for the Web service.5. Click Next and, if you like, enter aprefix for the proxy name.FIGURE 3 |PBDJ volume12 issue1131
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