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Maven属性替换

一、替换规则

参考：https://maven.apache.org/ref/3.8.4/maven-model-builder/

1）替换时间

属性替换发生在ModelBuilder构建effective pom时，主要流程包括：profile激活、合并重复依赖、profile注入、父pom解析直至super pom、父子pom模型继承合并、模型的属性替换（也称属性翻译，属性解释）。

也就是说属性替换发生在父子pom继承合并之后，含依赖继承合并、配置继承合并等。使用合并后的配置、内置配置、环境配置，进行pom中的变量替换。

2）优先级

pom中的变量${xxx}在替换时可能多个配置Context都含有，此时会依据以下顺序来获取。从下面的图可知，pom.xml中定义属性优先级比内置变量project.*低，无法覆盖它们。也就是说父pom中使用${project.version}声明的版本会依据子pom的版本来替换。

value evaluation result common examples
project.* - 内置属性 POM content (see POM reference) ${project.version} ${project.build.finalName} ${project.artifactId} ${project.build.directory}
project.basedir the directory containing the pom.xml file ${project.basedir}
project.baseUri the directory containing the pom.xml file as URI ${project.baseUri}
build.timestamp maven.build.timestamp the UTC timestamp of build start, in yyyy-MM-dd'T'HH:mm:ss'Z' default format, which can be overridden with maven.build.timestamp.format POM property ${maven.build.timestamp}
* - 命令行中-D属性 user properties, set from CLI with -Dproperty=value ${skipTests}
* - pom.xml中属性 model properties, such as project properties set in the pom ${any.key}
maven.home The path to the current Maven home. ${maven.home}
maven.version The version number of the current Maven execution (since 3.0.4). For example, “3.0.5“. ${maven.version}
maven.build.version The full build version of the current Maven execution (since 3.0.4). For example, “Apache Maven 3.2.2 (r01de14724cdef164cd33c7c8c2fe155faf9602da; 2013-02-19T14:51:28+01:00)“. ${maven.build.version}
maven.repo.local The repository on the local machine Maven shall use to store installed and downloaded artifacts (POMs, JARs, etc). ${user.home}/.m2/repository
* Java system properties (see JDK reference) ${user.home} ${java.home}
env.* * environment variables ${env.PATH}
settings.* Local user settings (see settings reference) ${settings.localRepository}

二、示例

1）父Pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>person</groupId>
    <artifactId>parent</artifactId>
    <packaging>pom</packaging>
    <version>1.0.0-SNAPSHOT</version>
    <properties>
        <prop-1>parent</prop-1>
        <prop-2>parent</prop-2>
    </properties>
    <dependencies>
      <!-- 和子pom.xml保留一个进行测试，效果一样-->
       <dependency>
            <groupId>${prop-1}</groupId>
            <artifactId>${prop-2}</artifactId>
            <version>${project.version}</version>
        </dependency>
    </dependencies>
</project>

2）当前pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <artifactId>person</artifactId>
        <groupId>parent</groupId>
        <version>1.0.0-SNAPSHOT</version>
    </parent>
    <artifactId>son</artifactId>
    <version>1.1.0-SNAPSHOT</version>
    <properties>
        <prop-1>son</prop-1>
        <project.version>1.2.0-SNAPSHOT</project.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>${prop-1}</groupId> <!-- 当前pom覆盖父pom属性，prop-1 -->
            <artifactId>${prop-2}</artifactId> <!-- 当前pom未定义，直接继承父pom属性，prop-2 -->
            <version>${project.version}</version> <!-- 当前pom尝试覆盖内置属性，但是失败 -->
        </dependency>
    </dependencies>
</project>

3）在当前Pom所在工程执行mvn clean compile报错如下：

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Could not find artifact son:parent:jar:1.1.0-SNAPSHOT

由此可看出最终生效的属性如下：

  • prop-1：当前pom属性，当前pom覆盖了父pom
  • prop-2：父pom属性，当前pom未定义该属性，继承自父pom
  • project.version：当前pom尝试覆盖优先级更高的内置属性，但是失败

# 参考

  1. 为什么我不能覆盖DependencyManagement导入的pom的版本

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