How to find if I need to exclude dependencies in a maven java project?

Question

I use both Intellij IDEA (2018.3.5) & Eclipse IDEs, but I prefer Intellij. I have a maven based Java project with multiple poms. I added some dependencies to one of the pom files. I need to find out if there are any dependency conflicts which could prevent the build from running when its deployed, and then exclude them. I tried the steps given below to find conflicts which could cause problems. Are they enough or do I need to do more ?

• Check if there are any compile time dependency conflicts with mvn clean install -DskipTests. Build was successful with no errors.

• Check if Intellij shows no problems under File > Project Structure > Problems. There are no problems.

I also saw the dependency tree with mvn dependency:tree -Dverbose. It has a lot of "omitted for duplicate" and "omitted for conflict with" items, but the build was successful. I don't see any errors though. Does this mean that everything is okay or do I have to do something more about these conflicts ?

Answer 1

The best way to tell if everything is fine with your application is to have good tests.

However normally one doesn't exclude transitive dependencies from project's <dependency> libraries. Doing it can potentially break the dependency in a subtle and hard to notice way. It's usually safer to remove the whole <dependency>.

There are few scenario when one should use <exclude>:

1. Dealing with incompatible transitive dependencies between different libraries e.g. A requires library C-1.0 but library B requires library C-2.0 while C-1.0 and C-2.0 can't coexist on the classpath.

2. Having transitive dependencies already provided by system e.g. deploying to Tomcat with additional JARs in the TOMCAT_HOME/lib directory.

If you decide to exclude a dependency it's important that you check the final artifact because sometimes plugins do weird things e.g. there were versions of maven-assembly-plugin affected by a bug that resulted in different dependencies being resolved during shaded JAR creation than maven-dependency-plugin used for compilation.