java - 为什么从 BOM 引用版本的 Maven 子项不起作用？

Question

我创建了这个示例 POM 文件，这样我就不需要在每个子项目中复制依赖版本。我的要求是不需要每个项目都提供第三方版本。每个项目都应从 bom 文件继承库版本。我根据 documentation of Maven dependencies 创建了示例.我的maven版本是Apache Maven 3.2.5

我收到以下错误

[INFO] Scanning for projects...
[ERROR] The build could not read 1 project -> [Help 1]
[ERROR]   
[ERROR]   The project org.test.testapp:test-app:1.0-SNAPSHOT (/Users/skoya/workspace/test-app/pom.xml) has 2 errors
[ERROR]     'dependencies.dependency.version' for junit:junit:jar is missing. @ line 22, column 17
[ERROR]     'dependencies.dependency.version' for commons-cli:commons-cli:jar is missing. @ line 26, column 17

根bom pom文件

<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>org.test</groupId>
        <artifactId>bom</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <packaging>pom</packaging>
        <name>test-dependencies-bom</name>
        <url>http://myorg.org</url>

        <properties>
                <commons-cli.version>1.3</commons-cli.version>
                <junit.version>3.8.1</junit.version>
        </properties>

        <modules>
            <module>test-dependencies</module>
        </modules>
</project>

test-dependencies/pom.xml

<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>org.test</groupId>
        <artifactId>test-parent-pom</artifactId>  
        <version>0.0.1-SNAPSHOT</version>
        <packaging>pom</packaging>

        <name>test-parent-pom</name>
        <url>http://maven.apache.org</url>
        <parent>
                <groupId>org.test</groupId>
                <artifactId>bom</artifactId>
                <version>0.0.1-SNAPSHOT</version>
        </parent>

        <prerequisites>
                <maven>3.0.0</maven>
        </prerequisites>


        <dependencies>
                <dependency>
                        <groupId>commons-cli</groupId>
                        <artifactId>commons-cli</artifactId>
                        <version>${commons-cli.version}</version>
                </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
                        <version>${junit.version}</version>
    </dependency>

        </dependencies> 
</project>

引用 bom 文件的 Maven 项目文件

<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.test.testapp</groupId>
  <artifactId>test-app</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>test-app</name>
  <url>http://maven.apache.org</url>
  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.test</groupId>
        <artifactId>bom</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
    </dependency>
    <dependency>
      <groupId>commons-cli</groupId>
      <artifactId>commons-cli</artifactId>
    </dependency>
  </dependencies>
</project>

Answer 1

有两个问题:

1. 为了导入依赖项，导入的 pom 项目 (test-dependencies/pom.xml) 应该在 <dependencyManagement> 中定义要导入的依赖项部分，而不仅仅是 <dependencies>正如在您的原始样本中所做的那样。
2. 导入该 pom 的项目需要导入声明依赖项的项目 (test-dependencies/pom.xml)，而不是父 pom.xml。

我通过进行以下更改解决了这个问题。

test-dependencies/pom.xml

<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>org.test</groupId>
  <artifactId>test-parent-pom</artifactId>  
  <version>0.0.1-SNAPSHOT</version>
  <packaging>pom</packaging>
  <name>test-parent-pom</name>
  <url>http://maven.apache.org</url>

  <parent>
    <groupId>org.test</groupId>
    <artifactId>bom</artifactId>
    <version>0.0.1-SNAPSHOT</version>
  </parent>

  <prerequisites>
    <maven>3.0.0</maven>
  </prerequisites>

  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>commons-cli</groupId>
        <artifactId>commons-cli</artifactId>
        <version>${commons-cli.version}</version>
      </dependency>
      <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>${junit.version}</version>
      </dependency>
    </dependencies>
  </dependencyManagement>
</project>

引用 bom 文件的 Maven 项目文件

<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/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.test.testapp</groupId>
  <artifactId>test-app</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>test-app</name>
  <url>http://maven.apache.org</url>
  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>org.test</groupId>
        <artifactId>test-parent-pom</artifactId>
        <version>0.0.1-SNAPSHOT</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
    </dependency>
    <dependency>
      <groupId>commons-cli</groupId>
      <artifactId>commons-cli</artifactId>
    </dependency>
  </dependencies>
</project>

在那之后，我能够构建并验证导入 pom 的项目是否引入了预期的依赖项:

mvn dependency:tree
...
[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) @ test-app ---
[INFO] org.test.testapp:test-app:jar:1.0-SNAPSHOT
[INFO] +- junit:junit:jar:3.8.1:compile
[INFO] \- commons-cli:commons-cli:jar:1.3:compile

请注意，它仍然成功地从父 pom.xml 中提取了属性中定义的版本号。这是构建项目的一种完全有效的方式。它只需要我描述的 2 项调整。