Those of us writing Java/J2EE applications are commonly asked to interface with other applications we don't control. Sometimes, these are other custom applications written and managed by other teams. Sometimes, these are vended applications. Often, these applications are on a different platform (e.g. .Net) and sometimes not even designed to be integrated easily with custom applications. I refer to these types of interfaces as external [application] interfaces. External interfaces like these are usually an unpleasant source of support issues. There are ways Java architects can design external interfaces so that they minimize these support headaches and the resources needed to support them.
The key to a minimizing support for external interfaces is insulating your Java applications from them. That is, limit and contain the number of direct dependencies between your Java applications and 3rd party applications. The insulation strategy I usually use is depicted in the graphic below. As an example 3rd party application, let's use a document management system (DMS). This type of product is frequently purchased (or provided open source) and not custom built. Furthermore, there are several DMS vendors and the possibility that an organization may want to upgrade the DMS product or change DMS vendors is always a possibility.
Establish a generic operational data store for needed external application data. This data store will be the source of external application data for all your custom Java applications. This means that your Java applications do not need to understand internals of the external application. Your Java applications will not be affected if the external application is upgraded or enhanced. Consider a DMS as an example. DMS product upgrades happen no matter which vendor you choose. Using this strategy, your Java applications will not be affected by product upgrades; only the extracts populating the data store might be.
The operational data store must be vendor neutral. That is, your operational data store should not contain vendor-specific tables or fields. You should be able to populate the operational data store from a different product without changing it. You should be able to upgrade the external product without changing this data store. In the case of a DMS, you might have Document and Document_Type tables. However, no fields or tables should be specific to the DMS you are using.
Only populate data needed by your custom applications. The only purpose of the operational data store is to insulate your custom applications from external product changes and upgrades. To copy data not needed by your applications is just making work for no benefit. You can always enhance the data store if new requirements arrive.
Establish a generic Java API to process actions and information updates. The classes and methods in this API must be vendor neutral so that your Java applications are not affected by product upgrades and changes. Of course, the code supporting the API will need to adapt to changes in the underlying external application. Using a DMS as an example, you might have a generic Document interface with methods like “addDocument()” and the like. This API should be product-neutral.
Record all actions and information updates for the interface API. For example, if the DMS product exposes functionality via web services, I'll record the SOAP request and response texts for each API call. Should a defect be reported, support developers will have information they need to contact the vendor right away.
I hope you find this strategy useful. As always, your input is welcome.
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