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last updated: 10-Jan-2007
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<p>This isn't so much a design as a list of why we made the decisions we did. If you
disagree with anything then feel free to let us know...</p>
<hr>
<h4>Logging</h4>
<p>Goals: 1) not replicate the work that has gone into other logging projects, 2)
make it fast, 3) make it pluggable so you're not tied to a particular solution.</p>
<p>Solution: use Jakarta Common's ultra thin
<a href="http://jakarta.apache.org/commons/logging.html">logger</a>. This will
automatically log to Log4J or JDK 1.4's logger. If you want it to log
somwehere else then you just need to write a simple wrapper.</p>
<p>Good: it's already written, it's robust, it works.</p>
<p>Bad: nothing really :)</p>
<hr>
<h4>Proxy</h4>
<p>To get transparent control when people close a connection we need to proxy the Connection
object itself. This is easy enough to do: create an object called ProxyConnection which
contains a real Connection and delegate everthing (except the close method) to the
Connection. The trouble with this solution is that the API to the Connection object changes
with each release of the JDK. This means you have to constantly update the proxy and deploy
different versions for different JDKs. Not nice.</p>
<p>JDK 1.3 introduces the Proxy class that does a lot of this delegation for you using
reflection. This makes it really easy and means that when the API changes everything still
works. Unfortunately, it won't work with JDK 1.2. So we have patched up some hand written
proxies that work with JDK 1.2 only. They are contained within a different source tree to the
main code. When you use Ant to build your jar (and you specify that you are targetting
JDK 1.2) then it copies over these patched classes before compilation. This is not
an ideal solution, but at least it should go away over time when we eventually drop support
for JDK 1.2 (which we're not in a rush to do, by the way).</p>
<p>Using reflection is slower. No doubt about it. Quick tests have shown that it might add
1 or 2 milliseconds to each database call. I suggest that this isn't really significant
and that the ease of use and maintainability outweigh this slight delay.</p>
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