shade for parameter resource: Cannot find 'resource' in class org.apache.maven.plugins.shade.resource.ManifestResourceTransformer

Question

I'm working on a maven project. I'm trying to integrate jmh benchmarking into my project. The pom.xml of my maven project...

<parent>
    <groupId>platform</groupId>
    <artifactId>platform-root</artifactId>
    <version>3.0-SNAPSHOT</version>
    <relativePath>../../pom.xml</relativePath>
</parent>

<artifactId>platform-migration</artifactId>
<packaging>jar</packaging>
<name>Platform Migration</name>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compile.source>1.7</maven.compile.source>
    <maven.compile.target>1.7</maven.compile.target>
    <jmh.version>1.1.1</jmh.version>
    <jersey-version>2.22.1</jersey-version>
    <uberjar.name>rest-benchmarks</uberjar.name>
</properties>


<dependencies>
    <dependency>
        <groupId>platform</groupId>
        <artifactId>platform-commons</artifactId>
        <version>${platform.version}</version>
    </dependency>

    <dependency>
        <groupId>platform</groupId>
        <artifactId>platform-persistence</artifactId>
        <version>${platform.version}</version>
    </dependency>

    <dependency>
        <groupId>platform</groupId>
        <artifactId>platform-testing</artifactId>
        <version>${project.version}</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.openjdk.jmh</groupId>
        <artifactId>jmh-core</artifactId>
        <version>${jmh.version}</version>
    </dependency>
    <dependency>
        <groupId>org.openjdk.jmh</groupId>
        <artifactId>jmh-generator-annprocess</artifactId>
        <version>${jmh.version}</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-client</artifactId>
        <version>${jersey-version}</version>
    </dependency>

</dependencies>


<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>3.0.0</version>
            <executions>
                <execution>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <transformers>
                            <transformer
                                implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <mainClass>org.openjdk.jmh.Main</mainClass>
                            </transformer>
                        </transformers>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

When I build my project using "mvn clean install", I got following error

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-shade-plugin:3.0.0:shade (default) on project platform-migration: Unable to parse configuration of mojo org.apache.maven.plugins:maven-shade-plugin:3.0.0:shade for parameter resource: Cannot find 'resource' in class org.apache.maven.plugins.shade.resource.ManifestResourceTransformer -> [Help 1]

I don't understand why this error is happening?

Answer 1

Found a cause of this affecting my own setup and am sharing here in case it helps others.

In my case, the cause is a parent pom containing the maven-shade-plugin configuration as well as my own pom. The way that Maven merges these works out incorrectly. It appears the Maven is matching the transformer tags in the order they appear and merging them.

To figure this out, use mvn help:effective-pom and look for the resulting maven-shade-plugin configuration. In my case, a <resource> tag was added to the ManifestResourceTransformer, and this resource matched the first entry in the parent pom's maven-shade-plugin configuration.

Adding an <id> to the <execution> eliminates the problem:

<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <executions>
      <execution>
        <id>shade-my-jar</id>
...

I suspect both configurations were using the same, default ID. So the key is that each execution of the plugin have a unique id.