没有版本的 maven 依赖

最近我在一个项目中做了一些改进，这是我的发现。Pom 文件中的许多依赖项没有指定版本，但是它们已经得到了解决。该项目由1个根模块和2个子模块组成。使用了聚合器模式，这意味着根本没有 DependencyManagement 部分。上层项目只是简单地聚合了2个模块，这就是它所做的全部工作。子项目并不把它当作父项目来引用。他们有不同的父母。我不能理解的是，无论是子项目本身还是它们的父项目(事实上，它也没有 DepencyManagement)都没有为某些依赖项指定版本。例如:

<dependency>
<groupId>javax.mail</groupId>
<artifactId>javax.mail-api</artifactId>
</dependency>
<dependency>
<groupId>com.sun.mail</groupId>
<artifactId>javax.mail</artifactId>
</dependency>
<dependency>
<groupId>com.sun.mail</groupId>
<artifactId>imap</artifactId>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jul-to-slf4j</artifactId>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
</dependency>

有人能帮我解决这个问题吗？Maven 是否使用某种默认策略来处理版本控制？默认策略是什么？

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It is impossible for maven to work without defining versions of the artifacts. They should be defined somewhere in dependencyManagement tag either in the submodule or parent. Please check your pom hierarchy. Use mvn help:effective-pom in the submodule directory of the project. Also you can use mvn dependency:tree in order to find out which artifacts - along with full artifact information including version numbers - are resolved in the result of dependency management.

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最佳答案

Ok, I think I'm gonna answer it myself. Of course I took a look at dependency:tree, but all the dependencies that I mentioned were first-level members of the tree. What I failed to notice right away, is that dependencyManagement is not present in the parent, but it is however present in the submodules, and what is more interesting it contains:

        <dependency>
<groupId>io.spring.platform</groupId>
<artifactId>platform-bom</artifactId>
<version>1.0.2.RELEASE</version>
<type>pom</type>
<scope>import</scope>
</dependency>

I've never used Spring IO Platform before, so this is a totally new concept for me. As it turns out the platform includes quite a few preconfigured dependencies: http://docs.spring.io/platform/docs/current/reference/htmlsingle/#appendix-dependency-versions

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Use 

mvn -P<my_profile_of_interest> help:effective-pom -Dverbose

Verbose mode (Since: 3.2.0) adds XML comments containing precise reference to a place where dependency declaration is coming from.

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Each maven dependency defined in the pom must have a version either directly or indirectly for example, through dependencyManagement or parent. That being said, if the version is not given, then the version provided in the dependencyManagement or the parent pom will be used.

For example: in the pom (only important sections are mentioned) given below, no version is provided for the artifact jstl. However, in the "mvn dependency:tree", it shows that jstl version 1.2 is included. And looking at the spring-boot-starter-parent, for the version 2.3.3.RELEASE pom, it includes jstl version 1.2.

<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.3.3.RELEASE</version>
</parent>


<dependencies>
....
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jstl</artifactId>
</dependency>
....
</dependencies>
小开

In my case if i was using Spring boot starter parent to manage all dependency and lombok version is managed by Spring boot , This problem was coming due to higher java version JAVA 11 . I exported JAVA 8 in to my compile time environment and after using JAVA 8 this problem was gone.


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