How to resolve "Dependency convergence error" when using maven enforcer plugin? - maven

Question

I am just trying to pickup with maven-enforcer-plugin using a small pom (before I jump in to my project pom which has 100+ dependencies.)
After I have added the enforcer plugin, I am seeing Dependency convergence error.
The pom.xml file is below (sorry its not tidy).
How can i fix the errors with out disabling the enforcer plugin.
Basically I want to understand the concept behind how to use dependencyConvergence rule.
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.demo</groupId>
<artifactId>enforcer</artifactId>
<version>0.0.1-SNAPSHOT</version>
<dependencyManagement>
<dependencies>
<!--
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.2.13.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aop</artifactId>
<version>5.2.13.RELEASE</version>
</dependency>
-->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>5.2.10.RELEASE</version>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.3.5</version>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-web</artifactId>
<version>5.4.5</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-enforcer-plugin</artifactId>
<version>3.0.0-M3</version>
<executions>
<execution>
<id>dependency-convergence</id>
<goals>
<goal>enforce</goal>
</goals>
<configuration>
<rules>
<dependencyConvergence/>
</rules>
</configuration>
</execution>
</executions>
<configuration>
<rules>
<dependencyConvergence />
</rules>
</configuration>
</plugin>
</plugins>
</build>
</project>
Does it mean that, I have to declare each non converging dependency in the dependencyManagement explicitly as in this version of pom.xml(added dependencies to dependencyManagement).
The problem with spring-context still exists as I have added it as direct dependency and then in the dependency management with different version.
Basically - am able to fix the error, but not able to grasp the rules crystal clear yet.
fix one - pom.xml - updated the version in dependency management to the one used explicitly. So now there is no need to give the version explicitly in dependencies. But this would require me to have access to dependencyManagment of parent pom. If my statement is right, this might not be the situation every time.
fix two pom.xml - excluded spring-context from spring-security-web and it worked. But if there are a dozen of exclusion to be done, its going to be a pain.
If this is the way to go about with the convergence rule? In an enterprise project with 100+ dependencies and 100+ of their transitive dependencies, then the Bill of Materials(BOM) is gonna be quite huge and take time to build. hhhmmm. (I agree, there is going to be more control over the versions used and using property like <xyz.version>, upgrades can be done easily).
I will very much appreciate if anyone can list down the rules involving convergence.

Answer 1

A dependency convergence error means that
the dependency is not in dependencyManagement
there are different versions of the dependency in the dependency tree
The typical resolution is to define an entry in dependencyManagement that resolves the issue or to import an appropriate BOM into the dependencyManagement.
This is best done in the main POM of a multi module project, but also possible in modules.
Note that it is better to leave out the <version> tag in the <dependencies> section so that dependencyManagement will be used everywhere.