1.Maven Enforcer plugin是什么鬼？
在說這個插件是什么前我們先思考這么一個問題：當我們開發人員進入項目組進行開發前，要准備開發環境，而領導總是會強調工具的統一，編譯環境的統一。比如要求所有開發人員使用JDK1.8進行開發。
開發人員接下來就是去下載指定版本的JDK，然后開始開發。但是如果開發人員的機器配置比較多，有好幾個版本的JDK，而他雖然下載了JDK1.8，但是忘記配置環境變量，很有可能他用了JDK1.6進行的編譯。
問題有了，該如何解決？ Maven Enforcer plugin就是來解決這類問題。Enforcer可以在項目validate時，對項目環境進行檢查。
2.Maven Enforcer plugin怎么用？
Enforcer配置后默認會在validate后執行enforcer:enforce,然后對項目環境進行檢查。拿上面對JDK的校驗為例，我們在pom.xml中配置插件。
<?xml version="1.0" encoding="UTF-8"?> <project> ... <build> <plugins> <plugin> <artifactId>maven-enforcer-plugin</artifactId> <version>1.4.1</version> <executions> <execution> <id>default-cli</id> <goals> <goal>enforce</goal> </goals> <phase>validate</phase> <configuration> <rules> <requireJavaVersion> <message> <![CDATA[You are running an older version of Java. This application requires at least JDK ${java.version}.]]> </message> <version>[${java.version}.0,)</version> </requireJavaVersion> </rules> </configuration> </execution> </executions> </plugin> </plugins> </build> <properties> <java.version>1.8</java.version> </properties> </project>
我本地配置沒有JDK1.8，按照我的期望，執行maven命令時應該會失敗。讓我們來執行命令 mvn validate 會打出如下日志告知我們JDK版本過低。
qyfmac$ mvn validate
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Build Order:
[INFO]
[INFO] AppFuse Modular Application
[INFO] AppFuse Modular Application - Core
[INFO] AppFuse Modular Application - Web (Spring MVC)
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building AppFuse Modular Application 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-enforcer-plugin:1.4.1:enforce (enforce-versions) @ stock ---
[WARNING] Rule 1: org.apache.maven.plugins.enforcer.RequireJavaVersion failed with message: You are running an older version of Java. This application requires at least JDK 1.8.
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] AppFuse Modular Application ........................ FAILURE [ 0.987 s]
[INFO] AppFuse Modular Application - Core ................. SKIPPED
[INFO] AppFuse Modular Application - Web (Spring MVC) ..... SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.886 s
[INFO] Finished at: 2015-09-22T15:37:04+08:00
[INFO] Final Memory: 16M/156M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:1.4.1:enforce (enforce-versions) on project stock: Some Enforcer rules have failed. Look above for specific messages explaining why the rule failed. -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
其實執行命令 mvn enforcer:enforce 也可以達到上面的效果。區別就是validate是maven全局命令，enforcer:enforce是只執行這個插件的命令。
這里要注意一點，執行enforcer:enforce時，id必須是default-cli（具體原因請參閱:http://stackoverflow.com/questions/24827194/maven-enforcer-plugin-missing-or-invalid-rules）,否則會報
The parameters 'rules' for goal org.apache.maven.plugins:maven-enforcer-plugin:1.4.1:enforce are missing or invalid
3.Maven Enforcer plugin標簽詳解
現在對這個插件的配置講解一下。
<plugin> <artifactId>maven-enforcer-plugin</artifactId> <version>1.4.1</version> <executions> <execution> <id>default-cli</id> －－一個執行實例的id <goals> <goal>enforce</goal> －－執行的命令 </goals> <phase>validate</phase> －－執行的階段 <configuration> <rules> －－規則 <requireJavaVersion> －－JDK的版本 <message> －－失敗后提示消息 <![CDATA[You are running an older version of Java. This application requires at least JDK ${java.version}.]]> </message> <version>[${java.version}.0,)</version> －－JDK版本規則 </requireJavaVersion> </rules> </configuration> </execution> </executions> </plugin>
Enforcer的rules除了控制JDK版本，還有很多其他規則，甚至可以通過它的接口自定義。
- alwaysFail - Always fail... used to test plugin configuration.
- alwaysPass - Always passes... used to test plugin configuration.
- banDistributionManagement - enforces that project doesn't have distributionManagement.
- bannedDependencies - enforces that excluded dependencies aren't included.
- bannedPlugins - enforces that specific plugins aren't included in the build.
- bannedRepositories - enforces to not include banned repositories.
- banTransitiveDependencies - enforces that project doesn't have transitive dependencies.
- dependencyConvergence - ensure all dependencies converge to the same version.
- evaluateBeanshell - evaluates a beanshell script.
- reactorModuleConvergence - enforces that a multi module build follows best practice.
- requireActiveProfile - enforces one or more active profiles.
- requireEnvironmentVariable - enforces the existence of an environment variable
- requireFilesDontExist - enforces that the list of files does not exist.
- requireFilesExist - enforces that the list of files does exist.
- requireFilesSize - enforces that the list of files exists and is within a certain size range.
- requireJavaVersion - enforces the JDK version.
- requireMavenVersion - enforces the Maven version.
- requireNoRepositories - enforces to not include repositories.
- requireOS - enforces the OS / CPU Architecture.
- requirePluginVersions - enforces that all plugins have a specified version.
- requirePrerequisite - enforces that prerequisites have been specified.
- requireProperty - enforces the existence and values of properties.
- requireReleaseDeps - enforces that no snapshots are included as dependencies.
- requireReleaseVersion - enforces that the artifact is not a snapshot.
- requireSameVersions - enforces that specific dependencies and/or plugins have the same version.
- requireUpperBoundDeps - ensures that every (transitive) dependency is resolved to it's specified version or higher.
You may also create and inject your own custom rules by following the maven-enforcer-rule-api instructions.
我們再寫一個例子。比如除了需要限制JDK外，我們還要限定maven版本，項目不得包含TestNG依賴，操作系統必須是mac os x 64位,項目版本號在執行install時必須是正式版本。
直接上代碼：
<?xml version="1.0" encoding="UTF-8"?> <project> ... <build> <plugins> <plugin> <artifactId>maven-enforcer-plugin</artifactId> <version>1.4.1</version> <executions> <execution> <id>default-cli</id> <goals> <goal>display-info</goal> <goal>enforce</goal> </goals> <phase>validate</phase> <configuration> <rules> <requireMavenVersion> <message> <![CDATA[You are running an older version of Maven. This application requires at least Maven ${maven.version}.]]> </message> <version>[${maven.version},)</version> </requireMavenVersion> <requireJavaVersion> <message> <![CDATA[You are running an older version of Java. This application requires at least JDK ${java.version}.]]> </message> <version>[${java.version}.0,)</version> </requireJavaVersion> <bannedDependencies> <!--是否檢查傳遞性依賴(間接依賴)--> <searchTransitive>true</searchTransitive> <excludes> <!--groupId[:artifactId][:version][:type][:scope][:classifier]-->
<exclude>org.testng:testng</exclude> </excludes> <message>don't use TestNG,must use JUnit</message> </bannedDependencies> <requireOS> <name>mac os x</name> <family>mac</family> <arch>x86_64</arch> <version>10.10.3</version> </requireOS> <requireProperty> <property>project.version</property> <message>"Project version must be specified."</message> <regex>.*(\d|-SNAPSHOT)$</regex> <regexMessage>"Project version must end in a number or -SNAPSHOT."</regexMessage> </requireProperty> </rules> </configuration> </execution> <execution> <id>enforce-install</id> <goals> <goal>enforce</goal> </goals> <phase>install</phase> <configuration> <rules> <requireProperty> <property>project.version</property> <message>"Project version must be specified."</message> <regex>.*(\d)$</regex> <regexMessage>"Project version must end in a number."</regexMessage> </requireProperty> </rules> </configuration> </execution> </executions> </plugin> </plugins> </build> <dependencies> ... <!--測試放開--> <!--<dependency>--> <!--<groupId>org.testng</groupId>--> <!--<artifactId>testng</artifactId>--> <!--<version>6.1.1</version>--> <!--<scope>test</scope>--> <!--</dependency>--> </dependencies> <properties> <java.version>1.7</java.version> <maven.version>3.3.3</maven.version> </properties> </project>
這里要說一下requireOS了，不支持表達式，必須准確的寫一個版本號，個人認為這個不好，不過可以把version注釋掉，不校驗操作系統的版本。
如果某些情況下不檢查環境，可以在maven命令上加一個 -Denforcer.skip=true 來跳過enforcer插件執行。
例如:mvn clean validate -Denforcer.skip=true
更多神奇的配置方式還請參閱官方網站 ：http://maven.apache.org/enforcer/maven-enforcer-plugin/index.html。