How to programatically invoke a maven dependency plugin

Question

I am trying to invoke maven-dependency-plugin programatically. i am using maven 3 version. the problem is that when i invoke it through pluginManager.executeMojo(session, execut

Answer 1

Here is an updated version of Mojo Executor designed for Maven 3:

package com.googlecode.boostmavenproject;

import java.util.Collections;
import org.apache.maven.execution.MavenSession;
import org.apache.maven.model.Plugin;
import org.apache.maven.plugin.MojoExecution;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugin.descriptor.PluginDescriptor;
import org.apache.maven.project.MavenProject;
import org.codehaus.plexus.util.xml.Xpp3Dom;
import org.apache.maven.plugin.BuildPluginManager;
import org.apache.maven.plugin.descriptor.MojoDescriptor;
import org.codehaus.plexus.configuration.PlexusConfiguration;
import org.codehaus.plexus.util.xml.Xpp3DomUtils;
import org.sonatype.aether.repository.RemoteRepository;

/**
 * Executes an arbitrary mojo using a fluent interface.  This is meant to be executed within the context of a Maven 2
 * mojo.
 *
 * Here is an execution that invokes the dependency plugin:
 * <pre>
 * executeMojo(
 *              plugin(
 *                      groupId("org.apache.maven.plugins"),
 *                      artifactId("maven-dependency-plugin"),
 *                      version("2.0")
 *              ),
 *              goal("copy-dependencies"),
 *              configuration(
 *                      element(name("outputDirectory"), "${project.build.directory}/foo")
 *              ),
 *              executionEnvironment(
 *                      project,
 *                      session,
 *                      pluginManager
 *              )
 *          );
 * </pre>
 * @see http://code.google.com/p/mojo-executor/
 */
public class MojoExecutor
{
    /**
     * Entry point for executing a mojo
     *
     * @param plugin The plugin to execute
     * @param goal The goal to execute
     * @param configuration The execution configuration
     * @param env The execution environment
     * @throws MojoExecutionException If there are any exceptions locating or executing the mojo
     */
    public static void executeMojo(Plugin plugin, String goal, Xpp3Dom configuration,
                                                                 ExecutionEnvironment env) throws MojoExecutionException
    {
        if (configuration == null)
            throw new NullPointerException("configuration may not be null");
        try
        {
            MavenSession session = env.getMavenSession();

            PluginDescriptor pluginDescriptor = env.getPluginManager().loadPlugin(plugin,
                Collections.<RemoteRepository>emptyList(), session.getRepositorySession());
            MojoDescriptor mojo = pluginDescriptor.getMojo(goal);
            if (mojo == null)
            {
                throw new MojoExecutionException("Could not find goal '" + goal + "' in plugin "
                                                                                 + plugin.getGroupId() + ":"
                                                                                 + plugin.getArtifactId() + ":"
                                                                                 + plugin.getVersion());
            }
            configuration = Xpp3DomUtils.mergeXpp3Dom(configuration,
                toXpp3Dom(mojo.getMojoConfiguration()));
            MojoExecution exec = new MojoExecution(mojo, configuration);
            env.getPluginManager().executeMojo(session, exec);
        }
        catch (Exception e)
        {
            throw new MojoExecutionException("Unable to execute mojo", e);
        }
    }

    /**
     * Converts PlexusConfiguration to a Xpp3Dom.
     *
     * @param config the PlexusConfiguration
     * @return the Xpp3Dom representation of the PlexusConfiguration
     */
    private static Xpp3Dom toXpp3Dom(PlexusConfiguration config)
    {
        Xpp3Dom result = new Xpp3Dom(config.getName());
        result.setValue(config.getValue(null));
        for (String name: config.getAttributeNames())
            result.setAttribute(name, config.getAttribute(name));
        for (PlexusConfiguration child: config.getChildren())
            result.addChild(toXpp3Dom(child));
        return result;
    }

    /**
     * Constructs the {@link ExecutionEnvironment} instance fluently
     * @param mavenProject The current Maven project
     * @param mavenSession The current Maven session
     * @param pluginManager The Build plugin manager
     * @return The execution environment
     * @throws NullPointerException if mavenProject, mavenSession or pluginManager
     *   are null
     */
    public static ExecutionEnvironment executionEnvironment(MavenProject mavenProject,
                                                                                                                    MavenSession mavenSession,
                                                                                                                    BuildPluginManager pluginManager)
    {
        return new ExecutionEnvironment(mavenProject, mavenSession, pluginManager);
    }

    /**
     * Builds the configuration for the goal using Elements
     * @param elements A list of elements for the configuration section
     * @return The elements transformed into the Maven-native XML format
     */
    public static Xpp3Dom configuration(Element... elements)
    {
        Xpp3Dom dom = new Xpp3Dom("configuration");
        for (Element e: elements)
            dom.addChild(e.toDom());
        return dom;
    }

    /**
     * Defines the plugin without its version
     * @param groupId The group id
     * @param artifactId The artifact id
     * @return The plugin instance
     */
    public static Plugin plugin(String groupId, String artifactId)
    {
        return plugin(groupId, artifactId, null);
    }

    /**
     * Defines a plugin
     * @param groupId The group id
     * @param artifactId The artifact id
     * @param version The plugin version
     * @return The plugin instance
     */
    public static Plugin plugin(String groupId, String artifactId, String version)
    {
        Plugin plugin = new Plugin();
        plugin.setArtifactId(artifactId);
        plugin.setGroupId(groupId);
        plugin.setVersion(version);
        return plugin;
    }

    /**
     * Wraps the group id string in a more readable format
     * @param groupId The value
     * @return The value
     */
    public static String groupId(String groupId)
    {
        return groupId;
    }

    /**
     * Wraps the artifact id string in a more readable format
     * @param artifactId The value
     * @return The value
     */
    public static String artifactId(String artifactId)
    {
        return artifactId;
    }

    /**
     * Wraps the version string in a more readable format
     * @param version The value
     * @return The value
     */
    public static String version(String version)
    {
        return version;
    }

    /**
     * Wraps the goal string in a more readable format
     * @param goal The value
     * @return The value
     */
    public static String goal(String goal)
    {
        return goal;
    }

    /**
     * Wraps the element name string in a more readable format
     * @param name The value
     * @return The value
     */
    public static String name(String name)
    {
        return name;
    }

    /**
     * Constructs the element with a textual body
     * @param name The element name
     * @param value The element text value
     * @return The element object
     */
    public static Element element(String name, String value)
    {
        return new Element(name, value);
    }

    /**
     * Constructs the element containg child elements
     * @param name The element name
     * @param elements The child elements
     * @return The Element object
     */
    public static Element element(String name, Element... elements)
    {
        return new Element(name, elements);
    }

    /**
     * Element wrapper class for configuration elements
     */
    public static class Element
    {
        private final Element[] children;
        private final String name;
        private final String text;

        public Element(String name, Element... children)
        {
            this(name, null, children);
        }

        public Element(String name, String text, Element... children)
        {
            this.name = name;
            this.text = text;
            this.children = children;
        }

        public Xpp3Dom toDom()
        {
            Xpp3Dom dom = new Xpp3Dom(name);
            if (text != null)
            {
                dom.setValue(text);
            }
            for (Element e: children)
            {
                dom.addChild(e.toDom());
            }
            return dom;
        }
    }

    /**
     * Collects Maven execution information
     */
    public static class ExecutionEnvironment
    {
        private final MavenProject mavenProject;
        private final MavenSession mavenSession;
        private final BuildPluginManager pluginManager;

        public ExecutionEnvironment(MavenProject mavenProject, MavenSession mavenSession,
                                                                BuildPluginManager pluginManager)
        {
            if (mavenProject == null)
                throw new NullPointerException("mavenProject may not be null");
            if (mavenSession == null)
                throw new NullPointerException("mavenSession may not be null");
            if (pluginManager == null)
                throw new NullPointerException("pluginManager may not be null");
            this.mavenProject = mavenProject;
            this.mavenSession = mavenSession;
            this.pluginManager = pluginManager;
        }

        public MavenProject getMavenProject()
        {
            return mavenProject;
        }

        public MavenSession getMavenSession()
        {
            return mavenSession;
        }

        public BuildPluginManager getPluginManager()
        {
            return pluginManager;
        }
    }
}

I will attempt to contribute my changes back into the official Mojo Executor plugin.

Answer 2

Folks, I think I get it. The problem is not in the version of Maven that I am using. It is in the configuration that I am using for invoking maven-dependency-plugin. The unpack goal of maven-dependency-plugin requires the following parameters: artifactItems, local, project, reactorProjects and remoteRepos. Here is the correct version of the configuration used for invoking the plugin:

<configuration>
    <artifactItems>
    <artifactItem>
      <groupId>com.sap.ldi.demo.calc</groupId>
      <artifactId>com.sap.ldi.demo.calc.cmd</artifactId>
      <version>0.1.3-SNAPSHOT</version>
      <type>jar</type>
      <overWrite>true</overWrite>
      <outputDirectory>target/demo-calc-stuff</outputDirectory>
      <includes>**/*.*</includes>
    </artifactItem>
  </artifactItems>
  <local>${localRepository}</local>
  <project>${project}</project>
  <reactorProjects>${reactorProjects}</reactorProjects>
  <remoteRepos>${project.remoteArtifactRepositories}</remoteRepos>
</configuration>`

Answer 3

Maven Plugins are not meant to be invoked programmatically.

They rely on values that are injected by the underlying plexus container.

So either you will have to find out how to inject those values or you will have to rely on the default mechanism.

One thing you can use is the Maven Invoker. With that, you can programmatically launch maven lifecycles, but they will execute in a separate VM. So if you need to change the model dynamically beforehand, you will need to serialize the model out to a temporary pom.xml and use that with maven invoker. This is heavy stuff, but I have done it successfully some two years ago.