Invoking My First Web Service With ColdFusion (Amazon Web Service)

Posted December 16, 2006 at 11:45 AM

Tags: ColdFusion

Not so long ago, I created my first web service. I figured it was time to see how the other half live (those that invoke web services, not create them). To test it out, I decided to invoke one of Amazon.com's web services. To start out, I had to register to use their eCommerce web service. Then, I had to dig through many many links to actually find some documentation on how to use this stuff. The whole Amazon Web Service (AWS) section is a bit confusing to someone who has never used it before. It is hard to differentiate between examples and pre-built solutions and documentation.

Finally, I figured it out, and worked out this small example to search for a book with the title "Muscle: Confessions of an Unlikely BodyBuilder." This happens to be an amazing book and for anyone who loves to workout, this is a must-read!

But anyway, onto the code:

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This was my first introduction to REST-style web service invocation. I had seen the phrase REST thrown around here and there, but never really understood what it meant. After doing some quick Googling, it looks like REST is basically a no-methodology-methodology???? Basically, it uses standard HTTP to invoke web services. The XML response is just returned as part of the generated file content. Sorry if this is grossly incorrect... like I said, this was my first time trying to even look it up.

So, as you can see, I invoke the web service using ColdFusion's CFHttp tag. Each argument to the web service is passed as a URL CFHttpParameter. You could just as easily put these values as part of the query string in the URL attribute of the CFHttp tag, but this way creates a much nicer structure that will be easier to manipulate programmatically.

The rest of it is just being able to traverse XML documents and perform some simple XPath xml searches. One thing that I do that I would like to touch upon is the removing of all name space attributes from the XML nodes:

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I do this because I am not very good at using XPath and ColdFusion's XmlSearch() method. The name space arguments seem to mess up the XPath search "//Item". However, if I go through and use a regular expression replace to strip out all xml node attributes that define a name space, the XPath works quite nicely. So, admittedly, this is a bit of a hack (I am altering the returned data), but it's the only way I know how to get it working. Plus, I couldn't care less about name spaces. I am not even sure yet what they are used for.

That's all there is to it. Quite easy. In fact, I found it was harder to find the web service definition than it was to eventually invoke it. And a final note: Please do not look at any of this as a BEST practice. This was my first time ever invoking a web service, so it's all trial and error.

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Reader Comments

Thanks, used your code as example to make an amazon cfc to do a couple of REST calls and utilize the amazon webservice. Currently working on http://www.utpabooks.com using amazon as the backbone.

Very cool post. I was curious if you had updated this to account for Amazons new authentication policy that went into place in August?

@Mark,

To be honest, I have not looked at Amazon's web services since this post :)

Please whats the difference between REST and SOAP? Why don't you use the normal <cfinvoke webservice=..........>??

@Leonard,

REST and SOAP are just two different ways to invoke a web service. CFInvoke is no more normal than CFHTTP for web services. It just depends on what kind of technologies you have available. In fact, you can post to a SOAP web service using CFHTTP (which is probably why they have a CFHttpParam of type:xml).

REST uses URL or FORM parametrs. SOAP posts XML packets.

I personally find CFHTTP easier to use and debug.

hi, when I dump xml for example from Amazon's API, how do I access the values of the blue struct nodes?

@BB,

Hi,

i have actually not used amazon's api before but you need to convert the xml to a coldfusion document object using XmlParse() function and use the XmlSearch() function to get values from each node.

Example: <cfset xmlRequest = XmlParse(strXml.Trim()) />

where strXml is the xml var returned

<cfset arrSearchNodes = XmlSearch(xmlRequest,"//node1/node2") />

where node1 is the root level of the xml object, node2 the next level and so on.

To retrieve values within the last node level

<cfoutput>#arrSearchNodes[1].firstName.XmlText#</cfoutput>

where firstName is the tag name of the xml returned

I also had problems removing soap from soap:nodeName but found a solution on one of Ben's articles http://www.bennadel.com/blog/494-Stripping-XML-Name-Spaces-And-Node-Prefixes-From-ColdFusion-XML-Data-To-Simplify-XPath-.htm

the article should provide u with as much information as possible cos i used it

hope it helps

@Leonard Inegbedion,

Hi thanks,

I got it finally with this. It returned "Translator"

tmp.ItemLookupResponse.Items[1].Item.ItemAttributes.Creator[1].XmlAttributes["Role"]

@BB,

Glad you got it working. You can typically thing of XML documents as structures and arrays. It gets a bit complicated with node names with namespaces and embedded dots (as @Leonard eludes to).

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