Why build-helper-maven-plugin throws the exception: 'Cannot find default setter in class org.apache.maven.model.Resource'?

Question

This is my build-helper-maven-plugin configuration in pom.xml:

 <plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <version>1.12</version>
    <executions>

      <execution>
        <id>add-extra-resources</id>
        <phase>generate-resources</phase>
        <goals>
          <goal>add-resource</goal>
        </goals>
        <configuration>
          <resources>
            <directory>src/main/python</directory>
            <!--<resource>src/main/python</resource>-->
          </resources>
        </configuration>
      </execution>
    </executions>

  </plugin>

when I run mvn install I got the following error:

[ERROR] Failed to execute goal org.codehaus.mojo:build-helper-maven-plugin:1.12:add-resource (add-extra-resources) on project spookystuff: Unable to parse configuration of mojo org.codehaus.mojo:build-helper-maven-plugin:1.12:add-resource for parameter directory: Cannot find default setter in class org.apache.maven.model.Resource -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.codehaus.mojo:build-helper-maven-plugin:1.12:add-resource (add-extra-resources) on project spookystuff: Unable to parse configuration of mojo org.codehaus.mojo:build-helper-maven-plugin:1.12:add-resource for parameter directory: Cannot find default setter in class org.apache.maven.model.Resource
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:212)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:863)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:199)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
    at org.codehaus.classworlds.Launcher.main(Launcher.java:47)
Caused by: org.apache.maven.plugin.PluginConfigurationException: Unable to parse configuration of mojo org.codehaus.mojo:build-helper-maven-plugin:1.12:add-resource for parameter directory: Cannot find default setter in class org.apache.maven.model.Resource
    at org.apache.maven.plugin.internal.DefaultMavenPluginManager.populatePluginFields(DefaultMavenPluginManager.java:662)
    at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getConfiguredMojo(DefaultMavenPluginManager.java:594)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:121)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:207)
    ... 21 more
Caused by: org.codehaus.plexus.component.configurator.ComponentConfigurationException: Cannot find default setter in class org.apache.maven.model.Resource
    at org.eclipse.sisu.plexus.CompositeBeanHelper.setDefault(CompositeBeanHelper.java:95)
    at org.codehaus.plexus.component.configurator.converters.composite.ObjectWithFieldsConverter.fromConfiguration(ObjectWithFieldsConverter.java:61)
    at org.codehaus.plexus.component.configurator.converters.composite.AbstractCollectionConverter.fromChildren(AbstractCollectionConverter.java:54)
    at org.codehaus.plexus.component.configurator.converters.composite.ArrayConverter.fromConfiguration(ArrayConverter.java:52)
    at org.eclipse.sisu.plexus.CompositeBeanHelper.convertProperty(CompositeBeanHelper.java:273)
    at org.eclipse.sisu.plexus.CompositeBeanHelper.setProperty(CompositeBeanHelper.java:210)
    at org.codehaus.plexus.component.configurator.converters.composite.ObjectWithFieldsConverter.processConfiguration(ObjectWithFieldsConverter.java:101)
    at org.codehaus.plexus.component.configurator.BasicComponentConfigurator.configureComponent(BasicComponentConfigurator.java:34)
    at org.apache.maven.plugin.internal.DefaultMavenPluginManager.populatePluginFields(DefaultMavenPluginManager.java:632)
    ... 24 more

What does this mean and how can I fix it?

Answer 1

Have a look at the documentation.

The right structure is:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <version>1.12</version>
    <executions>
        <execution>
            <id>add-extra-resources</id>
            <phase>generate-resources</phase>
            <goals>
                <goal>add-resource</goal>
            </goals>
            <configuration>
                <resources>
                    <resource>
                        <directory>src/main/python</directory>
                    </resource>
                </resources>
            </configuration>
        </execution>
    </executions>
</plugin>

You cannot set the the resource directly. So thats what Cannot find default setter in class org.apache.maven.model.Resource means.