DECIPHER: Dynamic XSLTs in BPEL (SOA 12c)

 While developing integrations in BPEL 12c, XSLT is most commonly used to transform different XML message structures. We generally come across scenarios wherein based on specific input fields, our transformation logic changes. What we generally do is have all conditions within the same XSLT file. This makes our XSLT look a lot bigger and difficult to maintain. A better way would be to have different XSLTs and move deciding factor out of XSLT. Once we create different XSLTs for specific use cases having the same output format, now the question will come how to configure these XSLTs to be picked at runtime? This blog is curated with answers to such and many more questions.

Let's take the example of account creation. There is a source application sending account information in an XML document which we need to update in a backend database. Now source system can send different types of address information like home address, business address, or shipping address. We get this information in the addressType input field. In the backend database, for each type of address, there are different fields in the backend database. There could various ways to handle this.

1. Create one single XSLT to handle all the scenarios using XSLT functions like if, choose-when, etc. One single XSLT file for all the scenarios, BPEL code will be easy to read. But this will lead to a huge XSLT file and will be a bit tricky to maintain. In the future, if we want to add new conditions for only secondary addresses, then regression testing might be required to ensure we don't hamper the other functionality.

2. Another way could be to have separate XSLTs for each scenario. As per the example, we have 3 scenarios. The address can be of type home, business, or shipping address.

We can have 3 XSLTs created for each scenario. Now maintainability of Transformation XSLT code will be a lot easier. These can now be configured using an if-else block within the BPEL process to decide which XSLT to pick. The BPEL process will look now similar to below.

3. Now suppose tomorrow we have a new condition added, then we need to add another block of "elseif" to accommodate this. This will make your BPEL code look bigger.
In SOA 12c we have below two functions that can be used to shorten the BPEL flow and use the XSLT dynamically. 
  • ora:processXSLT
  • ora:doXSLTransformForDoc

Both of the above functions support the location of the XSLT file and input XML. The above functions can be used in conjunction with DVM to fetch the location of XSLT and assign it to the input of the function.
For the same example, let's consider below DVM file as an example.

We can use the above DVM file to extract the location of XSLT that can be used. Suppose we store the conditional value in a variable called $addType(having one of the values in the home, business, or shipping). We can use DVM lookup to fetch the resulting XSLT file location that can be provided as input to the above-mentioned functions in an Assign activity. In case none of the conditions matches the default.xsl file can be used.

dvm:lookupValue("dvms/dynamicXSLT.dvm", "addressType",$addType, "xsltLocation", "transformations/default.xsl")

Let us assume the output value of the above expression is stored in variable $dynamicXSLT and input XML is stored in $input. The expression will be:

ora:processXSLT($dynamicXSLT, $input)
ora:doXSLTransformForDoc($dynamicXSLT, $input)

Both the above functions do a similar task. But there is one major difference. Suppose your XSLT requires extra complex parameters to be passed as input. In such scenarios ora:doXSLTransformForDoc comes real handy. In this function, we can pass key-value pairs of parameters that can be used within the XSLT.

For example, if our XSLT requires a parameter contact(as defined in XSLT) and the value is stored in the $Contact variable in the BPEL process. Now our function will look like.

ora:doXSLTransformForDoc($dynamicXSLT, $input, 'contact', $contact)


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