依赖关系管理中的java导入pom

3 月 Questions & Answers 760

从doc开始读

Do not attempt to import a pom that is defined in a submodule of the current pom. Attempting to do that will result in the build failing since it won't be able to locate the pom.

Never declare the pom importing a pom as the parent (or grandparent, etc) of the target pom. There is no way to resolve the circularity and an exception will be thrown.

When referring to artifacts whose poms have transitive dependencies the project will need to specify versions of those artifacts as managed dependencies. Not doing so will result in a build failure since the artifact may not have a version specified. (This should be considered a best practice in any case as it keeps the versions of artifacts from changing from one build to the next).

我有以下疑问：

a）第3点是什么意思

b）在第1点中，为什么maven无法找到子模块pom？子模块不是在父模块之前生成的吗

在第3点中，我需要对...When referring to artifacts whose poms have transitive dependencies the project will need to specify versions of those artifacts as managed dependencies...进行更清楚的说明

因此，让我们假设我们有project A，我们将在project B{}部分导入它。现在，创建项目A的人必须在其<dependencyManagement>部分提到项目A的所有可传递依赖项（而不是直接依赖项）的版本？对于项目A的所有可传递依赖项，谁能知道这些版本

我对第一点还有一个疑问。我创建了一个基本上没有java代码的带有超级模块和子模块的框架项目。因此，我将分享他们的POM。我们将看到构建获得成功，但根据第1点，情况不应如此

项目结构如下：

超级模块的pom如下：

<?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>com.home</groupId>
    <artifactId>my-project</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <name>my-project</name>
    <url>http://www.example.com</url>

    <modules>
        <module>./sub-module1/pom.xml</module>
    </modules>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>com.home</groupId>
                <artifactId>sub-module1</artifactId>
                <version>1.0-SNAPSHOT</version>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>


    <licenses>
        <license>
            <name>The Apache Software License, Version 2.0</name>
            <url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
            <distribution>repo</distribution>
        </license>
    </licenses>


    <build>
        <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
            <plugins>
                <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-jar-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.2</version>
                </plugin>
                <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
                <plugin>
                    <artifactId>maven-site-plugin</artifactId>
                    <version>3.7.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-project-info-reports-plugin</artifactId>
                    <version>3.0.0</version>
                </plugin>

            </plugins>
        </pluginManagement>
    </build>
</project>

子模块的pom如下所示：

<?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>com.home</groupId>
    <artifactId>sub-module1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>


    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>3.8.1</version>
            </dependency>
        </dependencies>
    </dependencyManagement>


    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>
    </dependencies>

</project>

当我执行mvn clean compile时，它构建得很好

另外，我看到即使子模块pom包装类型保持为jar，范围导入也不会抛出错误。它仍然编译得很好

对于未来的读者，我将总结答案。第1点和第2点都成立，但只有当POM1（父模块或超级模块）导入POM2（子模块或子模块），然后POM2需要POM1来解析依赖项时，才会给出错误

在第1点中，无法找到这一点。在第2点中，它将由于继承而被发现，但将创建一个循环

下面我举个例子，以便人们能够验证

超级模块POM

<?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>com.home</groupId>
    <artifactId>my-project</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>

    <name>my-project</name>
    <url>http://www.example.com</url>

    <modules>
        <module>./sub-module1/pom.xml</module>
    </modules>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>com.home</groupId>
                <artifactId>sub-module1</artifactId>
                <version>1.0-SNAPSHOT</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>org.jsoup</groupId>
                <artifactId>jsoup</artifactId>
                <version>1.8.3</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
        </dependency>
    </dependencies>


    <licenses>
        <license>
            <name>The Apache Software License, Version 2.0</name>
            <url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
            <distribution>repo</distribution>
        </license>
    </licenses>


    <build>
        <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
            <plugins>
                <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-jar-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.2</version>
                </plugin>
                <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
                <plugin>
                    <artifactId>maven-site-plugin</artifactId>
                    <version>3.7.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-project-info-reports-plugin</artifactId>
                    <version>3.0.0</version>
                </plugin>

            </plugins>
        </pluginManagement>
    </build>
</project>

子模块POM

<?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>com.home</groupId>
    <artifactId>sub-module1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>


    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>3.8.1</version>
            </dependency>
        </dependencies>
    </dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
        </dependency>
        <dependency>
            <groupId>org.jsoup</groupId>
            <artifactId>jsoup</artifactId>
        </dependency>
    </dependencies>

</project>

共 (1) 个答案

# 1 楼答案

b) In 1st point , why would maven not able to find the sub module pom ? Is not submodule build before the parent ?

子模块未安装/部署在GAV引用（maven缓存或远程Nexus repo）中

这意味着任何引用子模块pom的项目都不会在子模块GAV中找到所述pom，因为构建、安装和部署的是主项目GAV

正如khmarbaise在评论中添加的：

You should never do a <scope>import</scope> inside a project which is already defined as a submodule which means is listed one <module>..</module> entry. Because the resolution of the import scope will be done before the rest which will result in a fail of the build.

以及：

a) What does point 3 mean ?

这意味着<dependencies>部分应该声明一些<dependency>，其中只有<group>和<artifact>，而不是{}
版本将从导入的<dependencyManagement>获取
另见“Tracking managed dependency versions in Maven”
作为illustrated here，托管依赖项用于在父pom处锁定版本

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依赖关系管理中的java导入pom

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