mercredi 25 mai 2011

Git killer features

After 3 weeks of working with Git (the DCVS written by Linus Torwalds), I definitely can say that it is a great technology.

If you are asking yourself what you need to learn right now? What is the next major revolution in the IT world? Maybe, the answer will be Git.

What are the killer features of Git for me:
  • Distributed – I can develop normally even without Internet and access to the central repository. It’s a great feature to make small and concise commits while developing at home, during the weekend.
  • Rich history revision mechanism – the search within the log-history is wonderful. With
    git log –sSecurityManager
    I can find, for example, all commits that introduce or remove the SecurityManager class. Attention, the search is performed on the source code and not on the commit log. It’s a best tool for making the code live analysis.
  • Git bisect – automatically find a failing commit using the binary search and a set of unit tests. If you don’t use the CI server (shame on you :)), you can nevertheless quickly find a bad commit. Git bisect command will run the tests against the project snapshots. Each snapshot is associated with a particular commit. I did not try to use this command yet. But, the concept is great.
  • CMD – git is a command line based tool. You can script the commands, make aliasing etc. CMD speed up your productivity. Of course, for making the merge it’s not so trivial, but the guys from Eclipse will soon release a completely functional version of the plugin eGit.
  • git cherry-pick - reintegate an existing commit to the current branch. How many times you have forgot to switch to the correct branch before making a commit? I have been confronted with this painfull mistake quite often. Now you don't have to report your commit manually to the correct branch. The magic cherry-pick command will make it four you!

I have worked with git on Windows and Mac. Git for Mac is a stable and I have not noticed any problem. It is not the case for Windows...

Git remote tags problems

For running Git on Windows box, you have to install msysgit (I used 1.7.4.msysgit.0). The one problem I encountered with msysgit, it was that I could not push my tag to the remote repo. The command
git push --tags origin master
did not create a tag remotely. The same command executed on Mac did the job correctly

Git - pdf book about git

I can recommend to download a free PDF book "Git Community Book" about git from

As long as I learning Git, as more I understand its powerfull.

mardi 3 mai 2011

Tools : free screenshot capture

The tool of the day is gadwin printScreen (only for Windows users).

A really powerful and free screenshot capture tool that I used on my Windows box.

You can download it here

Log4j : Customize LoggingEvent for SMTPAppender


Recently I was confronted to the need of customizing the log4j message generation. When an exception occurs, the application should sent the email to the development team in the following format:

The error message should be enclosed by the corporation information represented by the header and footer. The problem is the application URL (marked by the red ellipse). This URL can be different depending on the environment where the application is running and throwing the exception. In the complex, industrial projects where exist many environments, this can be very helpful to determine which environment has a problem.

First of all, how set the footer and header? It’s quite simple, you have to use org.apache.log4j.EnhancedPatternLayout, in the parameter ConversionPattern, you put the header, footer and the message error with some additional information (date, class name which generated the exception, etc). The standard log4j distribution(log4j.jar file) does not contain the class EnhancedPatternLayout, you have to download the additional extras companion (here)

Pay particular attention to do not use org.apache.log4j.PatternLayout which contains some issues with synchronization (see the first paragraphe of the associated JavaDoc). PatternLayout class is still widely used and all exemples on Internet use it, but for make your code robust you don’t have to use it.

And what about the environment dependent URL ? How can I put the or in the log message? I found 2 solutions:
  1. Use ant or maven to replace a specific symbol in your log4j.xml ( when you are building the app. You can use filter resource maven plugin fot that. But is not the most elegant solution, because you will have a strong dependency with the build tool. For production system, it is not a choice.
  2. Use org.apache.log4j.EnhancedPatternLayout and %properties{key} mechanism
So first of all, you have to customize the SMTPAppender in order to put the specific information into the each message that will be sent. For that you have to subclass SMTPAppender and override the method append. Take a look on my test implementation:

The code is self documented. I put the URL to prod environment behind the key named "app".I hardcoded the value in order to make the explanation simpler. But in your production code you may get the correposnding value from properties file, from environment variable or from the database.

Next, the key “app” in the event property becomes available for Log4J runtime. You may see how I use it in my log4j.xml file (the 2nd screenshot).

The setProperty method is an extension point and the excellent example of a good designed API.

Updated : actually, there is a simpler method to inject the environment name into the log4j logging message - simply, change the ConversionPattern for each log4.propeperties file.