Ivan’s agile thinkings

Here are a few useful vi keystrokes I learned the other day (from colleagues and from the help system):

Searching without case-sensitivity – global switch:

:set ignorecase

Searching without case-sensitivity  – for a single pattern:

prefix the pattern with \c

Searching backwards:

? (rather than /)

Search again in the opposite direction:

N (rather than n)

Nothing too thrilling, but it makes using vi that little easier.

A while back I attempted to create a visualization of the relations that OpenJPA creates between the Java classes that it enhances – the intent was to help better understand a particularly intertwined persistent object graph and see if I couldn’t figure out why we were getting a few strange problems.

The initial approach I took was a hilarious trip into the land of sed, perl and graphviz.  It kinda looked like it worked, but didn’t actually

Time passed……more time passed……I learned more……more time passed…….and then I had the wacky notion of tying directly into the Enhancer that OpenJPA uses to create the persistence enabled classes.  I haven’t done the visualization yet, but this is what I learned about actually tying in an AuxiliaryEnhancer.

1. Create the AuxiliaryEnhancer

The following code is the minimal you will need.  Enter this and then compile – you will need OpenJPA and serp on your classpath.

package com.ij;

import org.apache.openjpa.enhance.PCEnhancer.AuxiliaryEnhancer;
import serp.bytecode.BCClass;
import serp.bytecode.BCMethod;
import org.apache.openjpa.meta.ClassMetaData;

public class Grapher implements AuxiliaryEnhancer {

    public void run(BCClass bc, ClassMetaData meta) {
        System.out.println("Running Enhancement");
    }

    public boolean skipEnhance(BCMethod m) {
         System.out.println("skipEnhance?");
         return false;
    }
}

2. Register the enhancer using jar based services

This is something I was only barely aware off – registering concrete implementations of services through jar file meta-data.

• Create a file in a META-INF/services/ directory called org.apache.openjpa.enhance.PCEnhancer$AuxiliaryEnhancer
  • Note the dollar sign! That one caught me out for a while: I couldn’t decide whether the dot notation or the dollar notation should be used to reference the nested class.
• This file should simply contain the fully qualified name of the Enhancer you wrote: com.ij.Grapher
• Jar this directory and the class file up and you should end up with a jar listing like this

ivan-jensens-computer:jar ivanjensen$ jar tvf ../grapher.jar
     0 Tue Dec 02 21:56:42 PST 2008 META-INF/
    60 Tue Dec 02 21:56:42 PST 2008 META-INF/MANIFEST.MF
     0 Tue Dec 02 21:54:28 PST 2008 META-INF/services/
    16 Tue Dec 02 21:30:44 PST 2008 META-INF/services/org.apache.renamed.openjpa.enhance.PCEnhancer$AuxiliaryEnhancer
     0 Tue Dec 02 21:55:16 PST 2008 com/
     0 Tue Dec 02 21:55:38 PST 2008 com/ij/
   771 Tue Dec 02 21:55:38 PST 2008 com/ij/Grapher.class
   465 Tue Dec 02 21:54:46 PST 2008 com/ij/Grapher.java

3. Add the new jar file to the enhancer classpath

I did this by adding my jar file to the classpath element of my ant script – pretty simple.

4. Re-enhance your classes

Re-enhance your classes and you will see the System.out.println statements all over your console.

 [openjpac] skipEnhance?

 [openjpac] skipEnhance?

 [openjpac] Running Enhancement

 [openjpac] skipEnhance?

 [openjpac] skipEnhance?

 [openjpac] skipEnhance?

 [openjpac] skipEnhance?

 [openjpac] skipEnhance?

 [openjpac] skipEnhance?

 [openjpac] skipEnhance?

One thing I noticed about this: I had to delete my persistent classes and re-enhance, only then would the ‘run’ method be called.  The skipMethod is called whether I delete the classes or not.  I don’t know what that means yet, but I’m sure I am about to find out.

Notes:

I was actually using a patched version of OpenJpa 1.0.1 (for various, non-amusing, reasons), but the patches shouldn’t affect this tutorial.

About two months ago I stumbled on the Software Engineering Radio podcast, and in my opinion it’s one of the best techy podcasts out there (anyone knows any different?).

There are currently 107 podcasts available and the 13 I’ve listened to (and listened to again) have been worth their virtual weight in gold.  There are a lot of interviews about many, many topics and the interviewees really know there stuff.

SE-Radio is an invaluable resource for the professional software developer.

I’ve rarely had to use a commit token.  The teams I’ve worked in generally edit unrelated source items as much as is possible.  Over the years I’ve read about various amusing items being used as commit tokens: rubber ducks, action figures, hats and little flags, to name a few.  The general idea is that you should physically have the token to be allowed to commit – meaning there are no updates made to the source repository so your changes will go in cleanly.

It is possible that this could be side-stepped though – Mr Naughty Committer might pretend to be holding the Pokémon and commit – how can the source repository be expected to know where Pikachu is at any given moment??

However, one of my colleagues had a great idea the other day – ‘The Ultimate Commit Token”.  Simply appropriate one of those single use password setups with a single key fob.  You could try borrowing it from your corporate VPN setup – I’m sure they wouldn’t miss it.

 Wire your pre-commit script into the server-side element and have the fob floating between developers.  Et Voila! One very annoying, yet extremely effective commit token!!!

I know, I know, it’s not very exotic looking, but fear not!  I reckon it would look natty glued to the back of Spud Of Nine.

It does for for programming, it’ll do for blogging – Hello World!