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?
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.
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.
对不起，我迟到了。
让我尝试使用mvn dependency:tree命令来解释两者的区别
考虑下面的例子
父母POM -我的项目
<modules>
<module>app</module>
<module>data</module>
</modules>
<dependencies>
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>19.0</version>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.9</version>
</dependency>
</dependencies>
</dependencyManagement>
子POM -数据模块
<dependencies>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
</dependency>
</dependencies>
子POM -应用程序模块(没有额外的依赖项，因此将依赖项留空)
<dependencies>
</dependencies>
在运行mvn dependency:tree命令时，我们得到如下结果
Scanning for projects...
------------------------------------------------------------------------
Reactor Build Order:
MyProject
app
data
------------------------------------------------------------------------
Building MyProject 1.0-SNAPSHOT
------------------------------------------------------------------------
--- maven-dependency-plugin:2.8:tree (default-cli) @ MyProject ---
com.iamvickyav:MyProject:pom:1.0-SNAPSHOT
\- com.google.guava:guava:jar:19.0:compile
------------------------------------------------------------------------
Building app 1.0-SNAPSHOT
------------------------------------------------------------------------
--- maven-dependency-plugin:2.8:tree (default-cli) @ app ---
com.iamvickyav:app:jar:1.0-SNAPSHOT
\- com.google.guava:guava:jar:19.0:compile
------------------------------------------------------------------------
Building data 1.0-SNAPSHOT
------------------------------------------------------------------------
--- maven-dependency-plugin:2.8:tree (default-cli) @ data ---
com.iamvickyav:data:jar:1.0-SNAPSHOT
+- org.apache.commons:commons-lang3:jar:3.9:compile
\- com.google.guava:guava:jar:19.0:compile
谷歌guava在每个模块(包括父模块)中都被列为依赖项，而apache commons仅在数据模块中被列为依赖项(甚至不在父模块中)
用我自己的话来说，你的父项目帮助你提供了两种依赖:
implicit dependencies : all the dependencies defined in the <dependencies> section in your parent-project are inherited by all the child-projects
explicit dependencies : allows you to select, the dependencies to apply in your child-projects. Thus, you use the <dependencyManagement> section, to declare all the dependencies you are going to use in your different child-projects. The most important thing is that, in this section, you define a <version> so that you don't have to declare it again in your child-project.
在我看来，<dependencyManagement>(如果我错了请纠正我)只是通过帮助您集中依赖项的版本而有用。它就像一种辅助功能。
作为最佳实践，您的<dependencyManagement>必须在父项目中，其他项目将继承它。一个典型的例子是通过声明Spring父项目来创建Spring项目。
