Maven Modules Building a Single Specific Module

Question

I have a multi-module Maven project with a parent project P and three sub-modules A  B  and C   Both B and C are war projects and both depend on A     I can type mvn compile in P and have all of the sub-modules properly compiled  The problem comes when I want to do operations for specific modules   I d like to be able to package a war for project B  but when I run the package command from B s directory  it complains that it can t find the dependencies for A     I understand from this question  Maven and dependent modules that perhaps Maven isn t really designed for this type of dependency resolution  but that begs the question of how do I package B      Do I have to run mvn package for the entire project hierarchy when I really just want B    Do I have to install snapshots of A into my local repository every time I want to package B      This second scenario isn t much fun when A is still under active development   Any best practices here

User · Answer

Take a look at my answer Maven and dependent modules     The Maven Reactor plugin is designed to deal with building part of a project   The particular goal you ll want to use it reactor make

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You say you  really just want B   but this is false   You want B  but you also want an updated A if there have been any changes to it   active development     So  sometimes you want to work with A  B  and C   For this case you have aggregator project P   For the case where you want to work with A and B  but do not want C   you should create aggregator project Q   Edit 2016  The above information was perhaps relevant in 2009  As of 2016  I highly recommend ignoring this in most cases  and simply using the -am or -pl command-line flags as described in the accepted answer  If you re using a version of maven from before v2 1  change that first

User · Answer

Any best practices here    Use the Maven advanced reactor options  more specifically   -pl  --projects         Build specified reactor projects instead of all projects -am  --also-make         If project list is specified  also build projects required by the list   So just cd into the parent P directory and run   mvn install -pl B -am   And this will build B and the modules required by B    Note that you need to use a colon if you are referencing an artifactId which differs from the directory name   mvn install -pl  B -am   As described here  https   stackoverflow com a 26439938 480894

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Maven absolutely was designed for this type of dependency   mvn package won t install anything in your local repository it just packages the project and leaves it in the target folder   Do mvn install in parent project  A   with this all the sub-modules will be installed in your computer s Maven repository  if there are no changes you just need to compile package the sub-module  B  and Maven will take the already packaged and installed dependencies just right   You just need to a mvn install in the parent project if you updated some portion of the code

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Say Parent pom xml contains 6 modules and you want to run A  B and F    lt modules gt           lt module gt A lt  module gt           lt module gt B lt  module gt           lt module gt C lt  module gt           lt module gt D lt  module gt           lt module gt E lt  module gt           lt module gt F lt  module gt     lt  modules gt    1- cd into parent project   mvn --projects A B F --also-make clean install   OR  mvn -pl A B F -am clean install   OR  mvn -pl A B F -amd clean install   Note  When you specify a project with the -am option  Maven will build all of the projects that the specified project depends upon  either directly or indirectly   Maven will examine the list of projects and walk down the dependency tree  finding all of the projects that it needs to build   While the -am command makes all of the projects required by a particular project in a multi-module build  the -amd or --also-make-dependents option configures Maven to build a project and any project that depends on that project  When using --also-make-dependents  Maven will examine all of the projects in our reactor to find projects that depend on a particular project  It will automatically build those projects and nothing else

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If you have previously run mvn install on project B it will have been installed to your local repository  so when you build package A Maven can resolve the dependency  So as long as you install project B each time you change it your builds for project A will be up to date   You can define a multi-module project with an aggregator pom to build a set of projects    It s also worthwhile mentioning m2eclipse  it integrates Maven into Eclipse and allows you to  optionally  resolve dependencies from the workspace  So if you are hacking away on multiple projects  the workspace content will be used for compilation  Once you are happy with your changes  run mvn install  on each project in turn  or using an aggregator  to put them in your local repository

[java] Maven Modules + Building a Single Specific Module

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