How to create additional jar file with contents of all modules during maven build? - maven

Question

I have a multi-module maven project (say project-xxx). Lets say it consists of 5 modules:
project-xxx (war)
--> module-1 (jar)
--> module-2 (jar)
--> module-3 (jar)
--> module-4 (jar)
--> module-5 (jar)
When the maven project is built, the war file is generated and it includes the jar files of the 5 modules as well.
Now, for a different purpose (i.e., deploy to a distributed cache, so we can run queries from command-line), I want to generate a single `jar' file as well which includes the java classes from all modules. I'm aware that it is against maven's philosophy to generate more than one artifact and I read this blog post and a few other questions on SO.
But creating this single jar file would greatly simplify a few other things in my project. What would be the best approach to go about generating this single jar file?

Answer 1

I am very much in favor of the one artifact per Maven project convention. That being said, if you need a single artifact that contains all of the classes for all of the modules, then make a dedicated single project to do so:
<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 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>your-group-id</groupId>
<artifactId>one-jar-to-rule-them-all</artifactId>
<version>your-version</version>
<dependencies>
<dependency>
<groupId>your-group-id</groupId>
<artifactId>module-1</artifactId>
<version>your-version</version>
</dependency>
.
.
.
<dependency>
<groupId>your-group-id</groupId>
<artifactId>module-5</artifactId>
<version>your-version</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>2.4.2</version>
<configuration>
<!--
This restricts the jar to classes from your group;
you may or may not want to do this.
-->
<artifactSet>
<includes>
<include>your-group-id</include>
</includes>
</artifactSet>
<createDependencyReducedPom>true</createDependencyReducedPom>
</configuration>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
This example project depends on each module and then uses the maven-shade-plugin to combine all of those modules together into a single jar artifact. You could also make this a child module of your parent project-xxx so it gets built by the reactor. This way, you can have both a war and an uber jar, but still keep the modularity of a standard Maven build.

Answer 2

I think you should consider introducing first separate profiles, so that profile1 would contain the configuration to result a proper war packaging. Profile2 could contain configuration using the maven-shade-plugin, in order to create an UBER jar out of your existing modules. Profiles are a very clean and maven-ish way to split different concerns.
For maven profiles see here. For the maven-shade-plugin see here.
Hope that helps.