Why does the maven-assembly-plugin descriptor say in its example site?

Question

Something that has always made me wonder with maven-assembly-plugin is that the jar-with-dependencies example file on the apache website has a TODO comment about a jarjar format.

Is this just an artifact of code that keeps getting copied through indefinitely or is there some actual reason behind that TODO on the sample file?

Answer 1

The documentation states the following

Use jar-with-dependencies as the descriptorRef of your assembly-plugin configuration in order to create a JAR which contains the binary output of your project, along its the unpacked dependencies.

So jar-with-dependencies creates a single JAR will all the class files of your project and also all the unpacked class files of your dependencies.

I'm guessing, "jarjar" refers to something like the Spring Boot Maven plugin does: it also creates a single JAR file, but the dependencies are included in their original JAR files, not unpacked. In contrast to the assembly plugin approach, this requires a custom class loader.

However, you should probably ask this question on the Maven mailing list. I just did so and will update this answer if I get any new information.

Updates

• In found out that this particular part of the web page (including the TODO) was added over 10 years ago. Apparently the TODO hasn't been changed since.

Answer 2

I suspect this is referring to a jarjar format, which repackages Java libraries and embeds them into your own distribution, to allow for no dependencies.

see: jarjar

In the context of the example file, which contains:

<assembly xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.3" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.3 http://maven.apache.org/xsd/assembly-1.1.3.xsd">
  <!-- TODO: a jarjar format would be better -->
  <id>jar-with-dependencies</id>
  <formats>
    <format>jar</format>
  </formats>
  <includeBaseDirectory>false</includeBaseDirectory>
  <dependencySets>
    <dependencySet>
      <outputDirectory>/</outputDirectory>
      <useProjectArtifact>true</useProjectArtifact>
      <unpack>true</unpack>
      <scope>runtime</scope>
    </dependencySet>
  </dependencySets>
</assembly>

I think the todo is to indicate that this is how this certain method is done, but that a jarjar would be better. That is, "here's how you do it, but you should do it this other way".