Maven：如何排除或设置提供给由其他依赖项拖动的依赖项

Question

I've problem that in large java project that is using maven to build it.
I've many dependencies that the main app is using like ( 40 ).

The problem is that those dependencies are dragging more dependencies
and some of them I can't and don't want to include in my final build
this is dependencies hell!!

How do I exclude the specific dependencies in maven in my main app pom ?
I don't want it in my app final deployment.

For example if I set this in my main pom, it doesn't put all the dependencies of spring-boot-starter-tomcat that are dragged from other dependencies in provided , only the top level .

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <scope>provided</scope>
</dependency>

Answer 1

Maven brings in all the dependencies that a library requires and builds it for the runtime. Most cases you would want this to happen as you dont want to go through each dependency of your dependencies and then their inner dependencies (its a hellish job to do, please don't do that). But in some cases you might want to avoid bringing in few inner dependencies as you have the same at project level, for those cases maven lets you exclude them by <exclusions> .

The below sample is from maven official documentation:

<project>
  ...
  <dependencies>
    <dependency>
      <groupId>sample.ProjectA</groupId>
      <artifactId>Project-A</artifactId>
      <version>1.0</version>
      <scope>compile</scope>
      <exclusions>
        <exclusion>  <!-- declare the exclusion here -->
          <groupId>sample.ProjectB</groupId>
          <artifactId>Project-B</artifactId>
        </exclusion>
      </exclusions> 
    </dependency>
  </dependencies>
</project>

For deeper knowledge go here

Hope this helps !!

Answer 2

If you set a dependency to scope provided , all the transitive dependencies below also become provided - unless the <dependencyManagement> overwrites the versions/scopes of the dependencies. Have a look at mvn dependency:tree to figure out.

The command mvn dependency:list will list you exactly what Maven considers a dependency of your project. In your final artifact, you can either set all the unwanted dependencies as provided or figure out below which artifact they are included and write exclude statements as @vizsatiz said.