Maven为什么要从远程存储库下载模块

Question

Given the following modules in my pom.xml

<modules>
  <module>core</module>
  <module>middle-layer</module>
  <module>top-layer</module>
<modules>

Where top-layer depends on middle-layer which depends on core.

When I run clean install it will build and install core and middle-layer successfully, but not top-layer. It tries to download middle-layer from a remote repository instead of using the freshly built one in the local repository.

I do have a custom remote repository specified in my pom.xml:

 <repositories>
    <repository>
        <id>custom</id>
        <url>http://someaddress/maven2/</url>
        <snapshots>
            <updatePolicy>never</updatePolicy>
        </snapshots>
        <releases>
            <updatePolicy>never</updatePolicy>
        </releases>
    </repository>
</repositories>

Why does it want to grab middle-layer from the remote repository?

Currently, everything is in SNAPSHOT-mode.

Middle layer dependency:

<dependencies>
    <dependency>
        <groupId>mygroup</groupId>
        <artifactId>core</artifactId>
        <version>2.0.1-SNAPSHOT</version>
    </dependency>
</dependencies>

Top layer dependency:

<dependencies>
    <dependency>
        <groupId>mygroup</groupId>
        <artifactId>middle-layer</artifactId>
        <version>2.0.1-SNAPSHOT</version>
    </dependency>
</dependencies>

They all inherent their versions from the parent (currently at 2.0.1-SNAPSHOT) and I'm calling install from the parent pom.

Answer 1

Maven frequently prints messages about downloading things that it is not, in fact, downloading. It is considering the possibility that there is a newer snapshot available remotely than the last one build locally. This is why uploading snapshots is often a really bad idea.

Answer 2

I found the answer.

It was a typical problem between keyboard and chair.

The middle-layer is actually historically a WAR, not a JAR, that is to say: it includes some classes I needed in my top-layer. (It's not really called middle-layer of course). So top-layer searches for middle-layer.jar and can't find it (because it's a WAR).

So I have to refactor some stuff to get the things I need from middle-layer into a new library JAR and make both middle-layer and top-layer depend on that instead.

Sorry to waste your time. :)