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Posted to users@maven.apache.org by Utku Gültopu <ug...@gmail.com> on 2016/06/07 20:04:11 UTC

Why does archetype plugin use -D before parameters?

Normally, -D is used to specify a system property to the JVM. However, when I check out the following invocation of the archetype plugin:

mvn archetype:generate -DgroupId=com.mycompany -DartifactId=SampleApp -DarchetypeArtifactId=maven-archetype-webapp -DinteractiveMode=false

The invocation is like:

java
	-classpath /usr/local/apache-maven-3.3.9/boot/plexus-classworlds-2.5.2.jar
	-Dclassworlds.conf=/usr/local/apache-maven-3.3.9/bin/m2.conf
	-Dmaven.home=/usr/local/apache-maven-3.3.9
	-Dmaven.multiModuleProjectDirectory=/Users/username/Documents/Maven_Archetype_Test
	org.codehaus.plexus.classworlds.launcher.Launcher archetype:generate
	-DgroupId=com.mycompany
	-DartifactId=SampleApp
	-DarchetypeArtifactId=maven-archetype-webapp
	-DinteractiveMode=false

Options coming after the class name (i.e, after "org.codehaus.plexus.classworlds.launcher.Launcher”) are passed to the main method of the application. Hence, the options

	-DgroupId=com.mycompany
	-DartifactId=SampleApp
	-DarchetypeArtifactId=maven-archetype-webapp
	-DinteractiveMode=false

are not sent to the JVM but to org.codehaus.plexus.classworlds.launcher.Launcher. Yet, these options “masquerade” as JVM options (unless these options are not set to be System Properties in Launcher class or somewhere else).

I wonder the reason for this. Why not simply specify the arguments as

	-groupId=com.mycompany
	-artifactId=SampleApp
	-archetypeArtifactId=maven-archetype-webapp
	-interactiveMode=false

but as

	-DgroupId=com.mycompany
	-DartifactId=SampleApp
	-DarchetypeArtifactId=maven-archetype-webapp
	-DinteractiveMode=false

?

Regards
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Re: Why does archetype plugin use -D before parameters?

Posted by ec...@zusammenkunft.net.
Maven uses the -D syntax for user properties (too). I guess this is just because it is familiar and "user options" for direct invocations was an afterthought. Properties works for all plugins but most of them are not used interactively/direct like the archetype plugin. I dont think it is particular good but its just the way it is. Commonly used properties in builds are things like -DskipTests=true

BTW you might not have noticed but there is a indirection at work. You set maven properties and the plugin has goals (aka mojos) which by default observe (those) properties. If you look at the goal documentation for an plugin you can see which of its settings have user properties or default expressions which expand properties with the ${name} syntax. This indirection is good if you run the goals in a pom, a bit more confusing for the interactive goals:

http://maven.apache.org/archetype/maven-archetype-plugin/generate-mojo.html

Gruss
Bernd

-- 
http://bernd.eckenfels.net

-----Original Message-----
From: "Utku Gültopu" <ug...@gmail.com>
To: users@maven.apache.org
Sent: Mi., 08 Juni 2016 0:28
Subject: Why does archetype plugin use -D before parameters?

Normally, -D is used to specify a system property to the JVM. However, when I check out the following invocation of the archetype plugin:

mvn archetype:generate -DgroupId=com.mycompany -DartifactId=SampleApp -DarchetypeArtifactId=maven-archetype-webapp -DinteractiveMode=false

The invocation is like:

java
	-classpath /usr/local/apache-maven-3.3.9/boot/plexus-classworlds-2.5.2.jar
	-Dclassworlds.conf=/usr/local/apache-maven-3.3.9/bin/m2.conf
	-Dmaven.home=/usr/local/apache-maven-3.3.9
	-Dmaven.multiModuleProjectDirectory=/Users/username/Documents/Maven_Archetype_Test
	org.codehaus.plexus.classworlds.launcher.Launcher archetype:generate
	-DgroupId=com.mycompany
	-DartifactId=SampleApp
	-DarchetypeArtifactId=maven-archetype-webapp
	-DinteractiveMode=false

Options coming after the class name (i.e, after "org.codehaus.plexus.classworlds.launcher.Launcher”) are passed to the main method of the application. Hence, the options

	-DgroupId=com.mycompany
	-DartifactId=SampleApp
	-DarchetypeArtifactId=maven-archetype-webapp
	-DinteractiveMode=false

are not sent to the JVM but to org.codehaus.plexus.classworlds.launcher.Launcher. Yet, these options “masquerade” as JVM options (unless these options are not set to be System Properties in Launcher class or somewhere else).

I wonder the reason for this. Why not simply specify the arguments as

	-groupId=com.mycompany
	-artifactId=SampleApp
	-archetypeArtifactId=maven-archetype-webapp
	-interactiveMode=false

but as

	-DgroupId=com.mycompany
	-DartifactId=SampleApp
	-DarchetypeArtifactId=maven-archetype-webapp
	-DinteractiveMode=false

?

Regards
---------------------------------------------------------------------
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For additional commands, e-mail: users-help@maven.apache.org


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