dependencyManagement和dependencies之间的区别是什么? 我在Apache Maven网站上看过文档。 在dependencyManagement下定义的依赖项似乎可以在其子模块中使用,而无需指定版本。

例如:

父项目(Pro-par)在dependencyManagement下定义了一个依赖项:

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8</version>
    </dependency>
 </dependencies>
</dependencyManagement>

然后在Pro-par的子函数中,我可以使用junit:

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

但是,我想知道是否有必要在父pom中定义junit ?为什么不在需要的模块中直接定义它呢?


当前回答

为了便于理解,这里作了解释。 dependencyManagement和dependencies之间的最终区别是声明和添加

其他回答

如果依赖项是在顶级pom的dependencyManagement元素中定义的,子项目就不必显式地列出依赖项的版本。如果子项目确实定义了一个版本,它将覆盖顶层中列出的版本 POM的依赖管理部分。也就是说,dependencyManagement版本仅为 当子进程没有直接声明版本时使用。

The documentation on the Maven site is horrible. What dependencyManagement does is simply move your dependency definitions (version, exclusions, etc) up to the parent pom, then in the child poms you just have to put the groupId and artifactId. That's it (except for parent pom chaining and the like, but that's not really complicated either - dependencyManagement wins out over dependencies at the parent level - but if have a question about that or imports, the Maven documentation is a little better).

After reading all of the 'a', 'b', 'c' garbage on the Maven site and getting confused, I re-wrote their example. So if you had 2 projects (proj1 and proj2) which share a common dependency (betaShared) you could move that dependency up to the parent pom. While you are at it, you can also move up any other dependencies (alpha and charlie) but only if it makes sense for your project. So for the situation outlined in the prior sentences, here is the solution with dependencyManagement in the parent pom:

<!-- ParentProj pom -->
<project>
  <dependencyManagement>
    <dependencies>
      <dependency> <!-- not much benefit defining alpha here, as we only use in 1 child, so optional -->
        <groupId>alpha</groupId>
        <artifactId>alpha</artifactId>
        <version>1.0</version>
        <exclusions>
          <exclusion>
            <groupId>zebra</groupId>
            <artifactId>zebra</artifactId>
          </exclusion>
        </exclusions>
      </dependency>
      <dependency>
        <groupId>charlie</groupId> <!-- not much benefit defining charlie here, so optional -->
        <artifactId>charlie</artifactId>
        <version>1.0</version>
        <type>war</type>
        <scope>runtime</scope>
      </dependency>
      <dependency> <!-- defining betaShared here makes a lot of sense -->
        <groupId>betaShared</groupId>
        <artifactId>betaShared</artifactId>
        <version>1.0</version>
        <type>bar</type>
        <scope>runtime</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>
</project>

<!-- Child Proj1 pom -->
<project>
  <dependencies>
    <dependency>
      <groupId>alpha</groupId>
      <artifactId>alpha</artifactId>  <!-- jar type IS DEFAULT, so no need to specify in child projects -->
    </dependency>
    <dependency>
      <groupId>betaShared</groupId>
      <artifactId>betaShared</artifactId>
      <type>bar</type> <!-- This is not a jar dependency, so we must specify type. -->
    </dependency>
  </dependencies>
</project>

<!-- Child Proj2 -->
<project>
  <dependencies>
    <dependency>
      <groupId>charlie</groupId>
      <artifactId>charlie</artifactId>
      <type>war</type> <!-- This is not a jar dependency, so we must specify type. -->
    </dependency>
    <dependency>
      <groupId>betaShared</groupId> 
      <artifactId>betaShared</artifactId> 
      <type>bar</type> <!-- This is not a jar dependency, so we must specify type. -->
    </dependency>
  </dependencies>
</project>

我在这个问题上迟到了,但我认为它值得一个比公认的回答更清晰的回答(公认的回答是正确的,但没有强调实际重要的部分,这需要您自己推断)。

在父POM中,<dependencies>和<dependencyManagement>之间的主要区别是:

Artifacts specified in the <dependencies> section will ALWAYS be included as a dependency of the child module(s). Artifacts specified in the <dependencyManagement> section, will only be included in the child module if they were also specified in the <dependencies> section of the child module itself. Why is it good you ask? Because you specify the version and/or scope in the parent, and you can leave them out when specifying the dependencies in the child POM. This can help you use unified versions for dependencies for child modules, without specifying the version in each child module.

我不建议使用dependencyManagement。

使用它的唯一好处是您可以在父pom中定义版本,而不需要在子pom中再次定义它。但是如果你有一组项目(特别是微服务项目)。使用dependencyManagement没有任何好处。

不同的项目可能需要不同的依赖关系。为什么要从同一个父pom继承它。尽可能保持简单。如果一个项目需要A依赖项,则将其添加到pom文件中。不要让开发人员感到困惑。

有几个答案概述了maven的< dependencies >和<dependencyManagement>标记之间的区别。

但是,下面简要阐述了几点:

<dependencyManagement> allows to consolidate all dependencies (used at child pom level) used across different modules -- clarity, central dependency version management <dependencyManagement> allows to easily upgrade/downgrade dependencies based on need, in other scenario this needs to be exercised at every child pom level -- consistency dependencies provided in <dependencies> tag is always imported, while dependencies provided at <dependencyManagement> in parent pom will be imported only if child pom has respective entry in its <dependencies> tag.