Monday, 16 February 2009

Analytic Workspace Manager Plugin Best Practices

The Analytic Workspace Manager (or AWM for short) is the tool to use when wanting to quickly create OLAP structures in the Oracle OLAP engine embedded within the Oracle relational database. Clearly you can use OWB etc. but AWM provides a lightweight easy to use interface for creating quick demos, restructuring content or processing etc. However, what the AWM provides may well not be everything to everyone and thus it is possible to create your own plugins, using Java, to get it to do what you want.

The documentation around doing this, I found, is a little light on the ground so to speak. So I have tried to document my findings here to help those that may wish to follow suit. However, before I start I should probably point out that in no way is the following post endorsed by Oracle. These are merely my observations after coding my own plugin for the Analytic Workspace Manager.

So here goes...
Step one is to find the Developing_AWM_Plugins_11g.pdf document. When I started coding my plugin for the 11g version of AWM, I could only find the 10g document which is not quite accurate for 11g. The OLAP API has changed somewhat in 11g and this is reflected in the OLAP API interface between the AWM and user plugin code. Looking at the document, I guess the pertinent points are that the 11g version of AWM requires the plugin to be compiled with Java 5 SE. (Or version 1.5 in "old school", just why did Sun confuse matters?) We'll come back to this but suffice to say that you'll need to remember that Java 5 brings with it support for generics.

Also in the document, if you have coded for 10g plugins, you may notice that the interface method signatures have changed a little. The AW object passed into the handle method is now an oracle.AWXML.AW object. The params parameter to the handle method provides a map, where the DATAPROVIDER key provides the ability to get a connection to the underlying Oracle database without requiring username/password information.

Step two, and arguably the most important step, is the understanding that on startup the Analytic Workspace Manager loads all Java code in the plugin directory and looks for any class files that implement the AWMPlugin interface. This is also documented in the above mentioned document, however, what is not made clear is that there will naturally be a performance impact on the startup time of AWM, the more classes and JAR files that you add to the plugin directory. Also, if you use 3rd-party JAR files you are at the mercy of those maintainers.

For example, placing the "jfreechart" JAR files in the plugin directory causes exceptions to be thrown in the AWM command window regarding missing Eclipse files. (I'm guessing that "jfreechart" is coded using Eclipse and some code dependencies are left behind.) Allowing this to happen with a user-defined plugin is pretty inelegant at best but most likely just down-right rude. We should avoid that, and we can.

The best practice I have come up with is as follows:
  • The interface between the AWM and your plugin should reside in its own JAR file and only contain the minimum number of class files etc. in order to start the actual plugin. This keeps the startup time for the AWM to the minimum.
  • The actual plugin code should be packaged into its own JAR file and placed elsewhere in the file system. (I use a subdirectory of the plugin directory so that it can be found using relative paths from the plugin interface.)
  • Associated plugin dependencies should also be placed into a subdirectory (I use the same one as my own code as mentioned above) of the plugin directory.
Now, Oracle kindly provide a directory from which plugins can be found and executed but this clearly isn't scalable from a startup point of view if you require the use of large dependencies or lots of plugins. Oracle unfortunately don't provide the equivalent of an "Ext" directory into which dependencies could be placed. So here's the dilemma... Do we customise the Windows batch file (or *nix shell script) to include our dependencies in the classpath, or do we place our dependencies in one of the directories that is already referenced by the Oracle prescribed classpath?

My answer... neither! Customising the startup script is prone to failure if Oracle ever decide to update it. It also means deploying the plugin is a pain, in that everyone's installation may be different so deploying the script needs to take that into consideration. Hijacking the Oracle directories is also pretty "rude" and prone to cause issues down the line, not to mention taking into consideration once again the uniqueness of each installation. No, best practice would be to customise a URLClassLoader in order to dynamically load the dependencies at runtime and start the plugin. This unfortunately requires the use of reflection and is a bit more long winded but it will be far more robust and stand you in good stead during further developments.

My plugin used both "log4j" and "jfreechart", both of which had to be loaded onto the classpath with "log4j" needing to be instantiated in order to log progress. I may blog more on this in detail in the future, as doing this can be tricky and I couldn't find a definitive guide on this on the web.

Finally, coming back to generics, note that the AWMPlugin interface needs to be backwards compatible and as such does not make use of generics. This tends to generates compiler warnings. The way I would recommend handling this is to annotate the interface methods with "@SuppressWarnings("unchecked")" to suppress those warnings but only on the methods provided by Oracle. If you need to assign one of the variables found in the interface parameter list to to your own variable, you can use the generic wildcard, such as declaring "Map<?>", indicating the supertype.

And that's all there is to it.

No comments:

Post a Comment