Today, I stumbled upon a classpath related problem – once again. As I doubt that I am the only one to ever face this problem, I want to share a short shell script that came to the rescue.

But first, what was the problem? After adding some additional dependencies to our POM – quite carelessly I have to admit – our application started sending mails without subject, sender address and messed up special characters. Interestingly enough, I didn’t touch the mail part at all. I added Apache CXF dependencies, i.e. web service stuff. So what was wrong?

CXF comes with quite a lot of transitive dependencies (that should be declared optional, I’d say), including some Geronimo Spec jars. One of them was org.apache.geronimo.specs:geronimo-javamail_1.4_spec that superseded classes from javax.mail:mail. A simple exclusion fixed the problem.

However, I wanted to be prepared for the next time as this tends to happen quite regularly with a growing number of transitive dependencies. There are packages with same content and different id, (e.g. org.mortbay.jetty:servlet-api and javax.servlet:servlet-api), artifacts that contain subsets of other artifacts (e.g. org.springframework:spring contains everything from org.springframework:spring-web), and artifacts that should be replaced in favor of others (e.g. slf4j instead of commons-logging.

That’s why I wrote this little bash script:

#!/bin/bash
for lib in `find . -name '*.jar'`; do
for class in `unzip -l $lib | egrep -o '[^ ]*.class$'`; do
class=`echo $class | sed s/\\.class// | sed s/[-.\/$]/_/g`
existing=$( eval "echo $CLS_${class}" )
if [ -n "$existing" ]; then echo "$lib $existing"; fi
eval CLS_${class}="("${lib} ${existing}")"
done
done | sort | uniq -c | sort -nr

These few lines of code print packages and the number of their common classes. Sample output is:

stf@crabman:/path/to/my/webapp$ duplicates.sh
127 ./WEB-INF/lib/aspectjweaver-1.5.3.jar ./WEB-INF/lib/aspectjrt-1.5.3.jar
117 ./WEB-INF/lib/spring-2.0.8.jar ./WEB-INF/lib/spring-web-2.0.8.jar
83 ./WEB-INF/lib/commons-beanutils-1.7.0.jar ./WEB-INF/lib/commons-beanutils-core-1.7.0.jar
38 ./WEB-INF/lib/servlet-api-2.3.jar ./WEB-INF/lib/servlet-api-2.5-6.1.11.jar
10 ./WEB-INF/lib/commons-beanutils-core-1.7.0.jar ./WEB-INF/lib/commons-collections-3.2.jar
10 ./WEB-INF/lib/commons-beanutils-1.7.0.jar ./WEB-INF/lib/commons-beanutils-core-1.7.0.jar ./WEB-INF/lib/commons-collections-3.2.jar
9 ./WEB-INF/lib/spring-2.0.8.jar ./WEB-INF/lib/aopalliance-1.0.jar
6 ./WEB-INF/lib/commons-logging-1.1.jar ./WEB-INF/lib/jcl104-over-slf4j-1.5.0.jar

The code isn’t very fast, but makes solving a common classpath problem a lot less painful. (Note that I am using plain unzip instead of jar as didn’t have a JDK installed on this server/)