Maven用户都应该知道的一些事：构建生命周期和插件
Maven的所有实际操作都是由插件完成的，如果没有插件，Maven什么都不会干。
（即时你没有在POM中配置<plugin>元素，Super POM中也已经帮你引入了若干核心插件）
那么问题来了，项目构建过程中，Maven是怎么知道应该在什么时候调用哪个插件的呢？
插件的调用时机，跟’生命周期’和’插件目标’有很大关系。
插件目标(Plugin Goal)是个什么鬼
首先需要知道的是，Maven的所有具体任务都是交由插件实现的，而一个插件往往能实现若干个任务或功能。又或者可以说一个插件能实现若干个目标，比如编译源码、执行测试用例、打包项目等等。
简单来说，在Maven中Plugin Goal可以看做是插件的一个功能。
Plugin Goal通常用‘插件前缀:插件目标‘的格式描述，常见的有：compiler:compile,surefire:test,dependency:tree等。
所谓插件前缀就是插件的名称的一个简写，比如compiler指的就是maven-complier-plugin这个插件。compiler:compile的意思既是maven-complier-plugin插件的compile目标。
构建生命周期(Build Lifecycle)又是什么
构建生命周期是对构建过程的抽象和统一，包括了几乎所有的构建步骤，如清理、初始化、编译、测试、打包等等。
Maven为不用的目的定义了3套相互独立的生命周期：
- clean 用于清理项目
- default 用于构建项目
- site 用于构建项目站点
每种生命周期都是由若干阶段(phase)组成，如clean生命周期由pre-clean,clean,post-clean三个阶段组成。
阶段之间是有序的，而且后面的阶段依赖前面的阶段。
用户执行mvn clean时，实际上maven会先执行pre-clean阶段，然后再执行clean阶段；执行mvn post-clean时，则会依次执行pre-clean,clean,post-clean三个阶段。
3个生命周期各自的阶段如下：
Clean Lifecycle
| Phase | Description |
|---|---|
| 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 |
Default Lifecycle
| Phase | Description |
|---|---|
| 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. |
Site Lifecycle
| Phase | Description |
|---|---|
| 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 |
插件目标与生命周期的绑定
插件目标是与生命周期的某个阶段绑定的，比如maven-clean-plugin的clean目标与clean阶段绑定，也就意味着当maven执行clean生命周期时，到达clean阶段的时候，会调用maven-clean-plugin的clean目标(删除项目输出目录)。
也就是说，插件目标的执行顺序是由其绑定到的生命周期阶段的顺序决定的，如果多个插件目标绑定到同一个阶段，那么先声明的插件会在后声明的插件之前执行。
对于一些核心插件，Maven已经内置默认将一些插件目标绑定到了生命周期阶段，特别是default生命周期，对于不同的打包类型（jar,war,pom等），Maven提供了不同的默认绑定。如下所示：
Clean Lifecycle Bindings
| Phase | plugin:goal |
|---|---|
| clean | clean:clean |
Default Lifecycle Bindings - Packaging ejb / ejb3 / jar / par / rar / war
| Phase | plugin:goal |
|---|---|
| process-resources | resources:resources |
| compile | compiler:compile |
| process-test-resources | resources:testResources |
| test-compile | compiler:testCompile |
| test | surefire:test |
| package | ejb:ejb or ejb3:ejb3 or jar:jar or par:par or rar:rar or war:war |
| install | install:install |
| deploy | deploy:deploy |
Default Lifecycle Bindings - Packaging ear
| Phase | plugin:goal |
|---|---|
| generate-resources | ear:generate-application-xml |
| process-resources | resources:resources |
| package | ear:ear |
| install | install:install |
| deploy | deploy:deploy |
Default Lifecycle Bindings - Packaging maven-plugin
| Phase | plugin:goal |
|---|---|
| generate-resources | plugin:descriptor |
| process-resources | resources:resources |
| compile | compiler:compile |
| process-test-resources | resources:testResources |
| test-compile | compiler:testCompile |
| test | surefire:test |
| package | jar:jar and plugin:addPluginArtifactMetadata |
| install | install:install |
| deploy | deploy:deploy |
Default Lifecycle Bindings - Packaging pom
| Phase | plugin:goal |
|---|---|
| package | |
| install | install:install |
| deploy | deploy:deploy |
Site Lifecycle Bindings
| Phase | plugin:goal |
|---|---|
| site | site:site |
| site-deploy | site:deploy |
参考文献
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