Maven 生命周期

1. Maven 构建生命周期

Maven 构建生命周期就是 Maven 将一个整体任务划分为一个个的阶段，类似于流程图，按顺序依次执行。也可以指定该任务执行到中间的某个阶段结束。
Maven 的内部有三个构建生命周期，分别是 clean, default, site。其中 default 生命周期的核心阶段如下所示：

2. 如何使用构建生命周期来完成构建工作

可以指定某个生命周期的阶段

执行 mvn install 命令，将完成 validate, compile, test, package, verify, install 阶段，并将 package 生成的包发布到本地仓库中。其中某些带有连字符的阶段不能通过 shell 命令单独指定。例如：(pre-, post-, or process-*)

mvn install

可以指定多个不同构建生命周期的阶段

执行 mvn clean deploy 命令，首先完成的 clean lifecycle，将以前构建的文件清理，然后再执行 default lifecycle 的 validate, compile, test, package, verify, insstall, deploy 阶段，将 package 阶段创建的包发布到远程仓库中。

mvn clean deploy

3. 阶段与插件的关系

如上所述，Maven 将构建过程定义为 default lifecycle，并将 default lifecycle 划分为一个个的阶段 phase，这一系列 phase 仅仅是规定执行顺序，至于每个阶段做什么工作？由谁来做？答案就在插件（plugins）中。
Maven 对工程的所有操作实实在在的都是由插件来完成的。一个插件可以支持多种功能，称之为目标（goal），例如：compiler 插件有两个目标：compile 和 testCompile，分别实现编译源代码和编译测试代码。
如何将插件与 Maven 的构建生命周期绑定在一起呢？通过将插件的目标（goal）与 build lifecycle 中 phase 绑定到一起，这样，当要执行某个 phase 时，就调用插件来完成绑定的目标。
如下图所示：从图中可以看出，每一个阶段可以绑定0 个或多个目标，每个插件可以提供 1 个或多个目标。

4. 如何为自己的工程创建构建生命周期

设置不同的 packaging 类型

在 pom.xml 文件中，packaging 类型支持 jar, war, ear, pom 等多种类型，不同的 packaging 类型会使得不同的 phase 绑定不同的 plugin goal。下面是 packaging 类型为 jar 时，phase 与 plugin goal 的映射关系。

阶段	目标
process-resources	resources:resources
compile	compiler:compile
process-test-resources	resources:testResources
test-compile	compiler:testCompile
test	surefire:test
package	jar:jar
install	install:install
deploy	deploy:deploy

配置 plugin

在 pom.xml 文件中， <build> <plugins> 元素下可以添加 <plugin>，通过指定 goal 和 phase 来进行绑定。
例如：将插件 modello-maven-plugin 的 java 目标绑定到 generate-sources 阶段。

<plugin><groupId>org.codehaus.modello</groupId><artifactId>modello-maven-plugin</artifactId><version>1.8.1</version><executions><execution><configuration><models><model>src/main/mdo/maven.mdo</model></models><version>4.0.0</version></configuration><phase>generate-sources</phase><goals><goal>java</goal></goals></execution></executions>
</plugin>

5. 我没有在 pom.xml 指定任何 plugin，但是也能正常构建工程

你可以能会疑问，默认的 pom.xml 文件并没有配置各种 plugin，但是也能正常构建工程？答案是 Maven 自己默认指定了 plugin。
下面是一个没有配置任何 plugin 的 pom.xml，执行 mvn install 的输出日志，从日志中可以看到一系列的插件(plugin):版本号:目标(phase)，例如 maven-resources-plugin:2.6:resources (default-resources)，maven-compiler-plugin:3.1:compile (default-compile) ，maven-resources-plugin:2.6:testResources (default-testResources)，maven-compiler-plugin:3.1:testCompile (default-testCompile)，maven-surefire-plugin:2.12.4:test (default-test)，maven-jar-plugin:2.4:jar (default-jar) ，maven-install-plugin:2.4:install (default-install)，

[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building my-app 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ my-app ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ my-app ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /Users/zhangguanghui/git/my-app/target/classes
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ my-app ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/zhangguanghui/git/my-app/src/test/resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ my-app ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /Users/zhangguanghui/git/my-app/target/test-classes
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ my-app ---
[INFO] Surefire report directory: /Users/zhangguanghui/git/my-app/target/surefire-reports-------------------------------------------------------T E S T S
-------------------------------------------------------
Running com.mycompany.app.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.004 secResults :Tests run: 1, Failures: 0, Errors: 0, Skipped: 0[INFO]
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ my-app ---
[INFO] Building jar: /Users/zhangguanghui/git/my-app/target/my-app-1.0-SNAPSHOT.jar
[INFO]
[INFO] --- maven-install-plugin:2.4:install (default-install) @ my-app ---
[INFO] Installing /Users/zhangguanghui/git/my-app/target/my-app-1.0-SNAPSHOT.jar to /Users/zhangguanghui/.m2/repository/com/mycompany/app/my-app/1.0-SNAPSHOT/my-app-1.0-SNAPSHOT.jar
[INFO] Installing /Users/zhangguanghui/git/my-app/pom.xml to /Users/zhangguanghui/.m2/repository/com/mycompany/app/my-app/1.0-SNAPSHOT/my-app-1.0-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.726 s
[INFO] Finished at: 2016-11-20T00:41:11+08:00
[INFO] Final Memory: 15M/310M
[INFO] ------------------------------------------------------------------------

5. 完整的 clean, default, site build lifecycle

clean lifecycle

phase	function
pre-clean execute	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	function
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	function
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