学习Maven之Maven Enforcer Plugin

1.Maven Enforcer plugin是什么鬼？

在说这个插件是什么前我们先思考这么一个问题：当我们开发人员进入项目组进行开发前，要准备开发环境，而领导总是会强调工具的统一，编译环境的统一。比如要求所有开发人员使用JDK1.8进行开发。

开发人员接下来就是去下载指定版本的JDK，然后开始开发。但是如果开发人员的机器配置比较多，有好几个版本的JDK，而他虽然下载了JDK1.8，但是忘记配置环境变量，很有可能他用了JDK1.6进行的编译。

问题有了，该如何解决？ Maven Enforcer plugin就是来解决这类问题。Enforcer可以在项目validate时，对项目环境进行检查。

2.Maven Enforcer plugin怎么用？

Enforcer配置后默认会在validate后执行enforcer:enforce,然后对项目环境进行检查。拿上面对JDK的校验为例，我们在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>

我本地配置没有JDK1.8，按照我的期望，执行maven命令时应该会失败。让我们来执行命令 mvn validate 会打出如下日志告知我们JDK版本过低。

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

其实执行命令 mvn enforcer:enforce 也可以达到上面的效果。区别就是validate是maven全局命令，enforcer:enforce是只执行这个插件的命令。

这里要注意一点，执行enforcer:enforce时，id必须是default-cli（具体原因请参阅:http://stackoverflow.com/questions/24827194/maven-enforcer-plugin-missing-or-invalid-rules）,否则会报

The parameters 'rules' for goal org.apache.maven.plugins:maven-enforcer-plugin:1.4.1:enforce are missing or invalid

3.Maven Enforcer plugin标签详解

现在对这个插件的配置讲解一下。

<plugin>
<artifactId>maven-enforcer-plugin</artifactId>
<version>1.4.1</version>
<executions>
  <execution>
    <id>default-cli</id>         －－一个执行实例的id
      <goals>
        <goal>enforce</goal>     －－执行的命令
      </goals>
      <phase>validate</phase>    －－执行的阶段
      <configuration>
        <rules>                  －－规则
          <requireJavaVersion>   －－JDK的版本
            <message>            －－失败后提示消息
              <![CDATA[You are running an older version of Java. This application requires at least JDK ${java.version}.]]>
             </message>
             <version>[${java.version}.0,)</version>   －－JDK版本规则
           </requireJavaVersion>
         </rules>
       </configuration>
    </execution>
  </executions>
</plugin>        

Enforcer的rules除了控制JDK版本，还有很多其他规则，甚至可以通过它的接口自定义。

• 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.

我们再写一个例子。比如除了需要限制JDK外，我们还要限定maven版本，项目不得包含TestNG依赖，操作系统必须是mac os x 64位,项目版本号在执行install时必须是正式版本。

直接上代码：

<?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>
                                    <!--是否检查传递性依赖(间接依赖)-->
                                    <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>
        ...
        <!--测试放开-->
        <!--<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>

这里要说一下requireOS了，不支持表达式，必须准确的写一个版本号，个人认为这个不好，不过可以把version注释掉，不校验操作系统的版本。

如果某些情况下不检查环境，可以在maven命令上加一个 -Denforcer.skip=true 来跳过enforcer插件执行。
例如:mvn clean validate -Denforcer.skip=true

更多神奇的配置方式还请参阅官方网站 ：http://maven.apache.org/enforcer/maven-enforcer-plugin/index.html。

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