Maven生命周期

重要概念

生命周期（Lifecycle）

Maven有三种不同的生命周期（Lifecycle），分别是Clean、Default、Site。每个生命周期又包含不同的阶段（Phase）。

阶段（Phase）

当我们在运行一个命令的时候，该命令都会对应某个生命周期的某个阶段，并且该生命周期中的在此阶段之前的命令都会被执行。比如，mvn clean 等同于 mvn pre-clean clean ，如果我们运行 mvn post-clean ，那么 pre-clean，clean 都会被运行。这是Maven很重要的一个规则，可以大大简化命令行的输入。

目标（goal）

具体某个阶段应该做什么工作，怎么做，Maven有默认的行为，当然也可以通过插件进行定制修改。这就引入了Maven中另一个重要概念：goal。一个phase可以绑定很多个goal，至少为一个，没有goal的phase是没有意义的。goal也是按顺序执行的，一个phase被执行时，绑定到phase里的goal会按绑定的时间被顺序执行，不管phase己经绑定了多少个goal，你自己定义的goal都可以继续绑到phase中。

mojo

Lifecycle与Phase与goal都是概念上的东西，mojo才是做具体事情的，可以简单理解mojo为goal的实现类，它继承于AbstractMojo，有一个execute方法，goal等的定义都是通过在mojo里定义一些注释的anotation来实现的，maven会在打包时，自动根据这些anotation生成一些xml文件，放在plugin的jar包里。

lifecycle与phase与goal就是级别的大小问题，引用必须是从高级引用下级（goal绑定到phase，执行时，phase会调用绑定到它那的goal），也不能跨级引用，如lifecycle可以引用任意的phase，不同lifecycle可以同时引用相同的phase，lifecycle不能跨级引用goal。goal会绑定到任意的phase中，也就是说不同的phase可以同时引用相同的goal，所以goal可以在一个lifecycle里被重复执行。

Clean Lifecycle

在进行真正的构建之前进行一些清理工作，Clean声明周期包含如下三个Phase。

pre-clean	execute processes needed prior to the actual project cleaning
clean	remove all files generated by the previous build
post-clean	execute processes needed to finalize the project cleaning

比如，我们在执行mvn clean的时候，其实是让Maven做它的Clean生命周期中的clean阶段应该去做的工作（当然，包含Clean生命周期中clean阶段之前的所有阶段的工作）。

Default Lifecycle

构建的核心部分，编译，测试，打包，部署等等。

validate	validate the project is correct and all necessary information is available.
initialize	initialize build state, e.g. set properties or create directories.
generate-sources	generate any source code for inclusion in compilation.
process-sources	process the source code, for example to filter any values.
generate-resources	generate resources for inclusion in the package.
process-resources	copy and process the resources into the destination directory, ready for packaging.
compile	compile the source code of the project.
process-classes	post-process the generated files from compilation, for example to do bytecode enhancement on Java classes.
generate-test-sources	generate any test source code for inclusion in compilation.
process-test-sources	process the test source code, for example to filter any values.
generate-test-resources	create resources for testing.
process-test-resources	copy and process the resources into the test destination directory.
test-compile	compile the test source code into the test destination directory
process-test-classes	post-process the generated files from test compilation, for example to do bytecode enhancement on Java classes. For Maven 2.0.5 and above.
test	run tests using a suitable unit testing framework. These tests should not require the code be packaged or deployed.
prepare-package	perform any operations necessary to prepare a package before the actual packaging. This often results in an unpacked, processed version of the package. (Maven 2.1 and above)
package	take the compiled code and package it in its distributable format, such as a JAR.
pre-integration-test	perform actions required before integration tests are executed. This may involve things such as setting up the required environment.
integration-test	process and deploy the package if necessary into an environment where integration tests can be run.
post-integration-test	perform actions required after integration tests have been executed. This may including cleaning up the environment.
verify	run any checks to verify the package is valid and meets quality criteria.
install	install the package into the local repository, for use as a dependency in other projects locally.
deploy	done in an integration or release environment, copies the final package to the remote repository for sharing with other developers and projects.

我们最常用的就是mvn package 或者mvn install 或者mvn compile了。

Site Lifecycle

生成项目报告，站点，发布站点。

pre-site	execute processes needed prior to the actual project site generation
site	generate the project's site documentation
post-site	execute processes needed to finalize the site generation, and to prepare for site deployment
site-deploy	deploy the generated site documentation to the specified web server

参考

Maven生命周期详解

Maven plugin中的lifecycle、phase、goal、mojo概念及作用的理解

Introduction to the Build Lifecycle

What are Maven goals and phases and what is their difference?