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Does anyone have code to detect duplicate JARs in the classpath?
Background: When there are two versions of the same JAR in the classpath, really strange things can happen. This can even happen when using tools like Maven: Change a dependency and build the WAR without cleaning first. Since target/webapp/WEB-INF/lib wasn't cleaned, the dependency will be in there twice.
Is there a safety-net for this?
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To check our CLASSPATH on Windows we can open a command prompt and type echo %CLASSPATH%. To check it on a Mac you need to open a terminal and type echo $CLASSPATH.
The, the idea is to use find on the root of your classpath to locate all jars, then runs findclass.sh on all found jars to look for a match. It doesn't handle multi-directories, but if you carefully choose the root you can get it to work.
Another way of viewing the classpath is to run this Java code: String classpath = System. getProperty("java. class.
JBoss Tattletale might help you with this.
It's a free tool which scans the JAR files used by your project and gives you a report about them.
Amongst its feature are:
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There is a Maven plugin to do just that: maven-duplicate-finder-plugin
[EDIT] If you want to do it in unit tests yourself, use
getClass().getClassLoader().getResources( "com/pany/package/Java.class" ) If this returns more than one URL, you have duplicates on the classpath.
The drawback is that this only works for cases where you had conflicts in the past. On the positive side, it's just a few lines of code (or one line when you write a helper method) and it works on your build server.
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