maven - advice on usage of multi-modules (jar, war, …) project

I have the following Maven organization:

- ./pom.xml (top-level project, which defines the 4 modules below)
   - ./a/pom.xml (library jar)
   - ./b/pom.xml (library jar)
   - ./c/pom.xml (war)
   - ./d/pom.xml (executable jar)

For building and deploying the c project, I do:

mvn verify tomcat7:redeploy -pl c -am

For building and executing the d project, I do:

mvn verify exec:java -pl d -am

For d there is a problem. Maven reports:

[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.4.0:java (default-cli)
on project parent: The parameters 'mainClass' for goal
org.codehaus.mojo:exec-maven-plugin:1.4.0:java are missing or invalid -> [Help 1]

This is indeed correct, the parent pom.xml has no configuration for exec. Only the d project has a configuration for exec.

This question is a little variation of question maven - advice on usage of multi-modules (jar, war, ...) project, so I decided to dedicate a separate question for it.

Why does Maven try to exec on the parent project?

update

I abstracted the same problem in following three pom files:

The parent pom:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>test</groupId>
    <artifactId>parent</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>parent</name>

    <modules>
        <module>a</module>
        <module>b</module>
    </modules>

    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>exec-maven-plugin</artifactId>
                    <version>1.4.0</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

The a pom:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>test</groupId>
        <artifactId>parent</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <artifactId>a</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>a</name>
</project>

The b pom:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>test</groupId>
        <artifactId>parent</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <artifactId>b</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>b</name>

    <dependencies>
        <dependency>
            <groupId>test</groupId>
            <artifactId>a</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <configuration>
                    <mainClass>MyMainClass</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

The command I am executing is:

mvn verify exec:java -pl b -am

This can also be found at https://github.com/jeperjaperjieper/issue-33197130.

Solution

I can't cure your problem, but I can give you a recipe. You may have hit a maven issue.

You don't have to use -pl and build from the top every time.

I would expect it to work if you just run 'mvn' (no -pl) at the top; it probably doesn't take very long to build the first pieces.

If you don't want to do that, then you need to run 'mvn install' for the pieces that come first, and then you'll be able to cd into the last piece and build it.

I recommend opening up a JIRA issue for Maven on this; it seems as if you've exposed a problem with -pl, but the best way to find out is to post an issue with a test case and poke the Maven user mailing list.