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?
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>
