------
 Introduction
 ------
 Dan Fabulich
 ------
 2008-08-15
 ------

~~ Licensed to the Apache Software Foundation (ASF) under one
~~ or more contributor license agreements.  See the NOTICE file
~~ distributed with this work for additional information
~~ regarding copyright ownership.  The ASF licenses this file
~~ to you under the Apache License, Version 2.0 (the
~~ "License"); you may not use this file except in compliance
~~ with the License.  You may obtain a copy of the License at
~~
~~   http://www.apache.org/licenses/LICENSE-2.0
~~
~~ Unless required by applicable law or agreed to in writing,
~~ software distributed under the License is distributed on an
~~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
~~ KIND, either express or implied.  See the License for the
~~ specific language governing permissions and limitations
~~ under the License.

Maven 2 Reactor Plugin

 This plugin can build a subset of interdependent projects in a
 reactor.  It should be useful in large reactor builds that include
 irrelevant stuff you're not working on.

* Goals Overview

  The Reactor plugin has several goals:

  * {{{./resume-mojo.html}reactor:resume}} resumes a reactor at a certain point (e.g. when it fails
    in the middle)

    Example: <<<mvn reactor:resume -Dfrom=bar>>>

  * {{{./make-mojo.html}reactor:make}} builds a project X and all of the reactor projects on which X depends

    Example: <<<mvn reactor:make -Dmake.folders=foo,bar>>>

  * {{{./make-dependents-mojo.html}reactor:make-dependents}}  builds a project X and all of the reactor projects that depend on X (the reverse of reactor:make)

    Example: <<<mvn reactor:make-dependents -Dmake.folders=foo,bar>>>

  * {{{./make-scm-changes-mojo.html}reactor:make-scm-changes}}  build all reactor projects that you personally
     have changed (according to SCM) and all reactor projects that depend
     on your changes

     Example: <<<mvn reactor:make-scm-changes>>>

* make vs. make-dependents

  The goals <<<reactor:make>>> and <<<reactor:make-dependents>>> are very similar.  They differ in the <direction> of dependency analysis.

  For example, suppose project "fooUI" depends on project "barBusinessLogic", which depends on project "bazDataAccess".

+---+
fooUI --> barBusinessLogic --> bazDataAccess
+---+

  Ordinarily, when building, you'll first build bazDataAccess, then barBusinessLogic, then fooUI.

  * <<make>>: In order to "make" barBusinessLogic, you first have to build bazDataAccess.  So if you run reactor:make on barBusinessLogic, it will build bazDataAccess, and then build barBusinessLogic; it won't build fooUI.  (This should remind you of the traditional "make" tool.)

+---+
barBusinessLogic --> bazDataAccess
+---+

  * <<make-dependents>>: Because fooUI depends on barBusinessLogic, fooUI is a "dependent" project of barBusinessLogic.  Anything that depends on barBusinessLogic is one of barBusinessLogic's "dependents."  Hence, reactor:make-dependents will build barBusinessLogic, and then build fooUI.

+---+
fooUI --> barBusinessLogic
+---+

  []

  <<In other words, reactor:make walks *down* the dependency tree, whereas reactor:make-dependents walks *up* the dependency tree.>>

* Examples

  To provide you with better understanding on some usages of the Reactor
  Plugin, you can take a look at the {{{./examples.html}examples}} page.