Error extracting plugin descriptor: 'Goal: * already exists in the plugin descriptor for prefix: *

 Error extracting plugin descriptor: 'Goal: validate already exists in the plugin descriptor for prefix: test

I was getting the below error while installing the Maven plugin - mvn clean install

org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-plugin-plugin:3.2:descriptor (default-descriptor) on project test: Error extracting plugin descriptor: 'Goal: validate already exists in the plugin descriptor for prefix: test
Existing implementation is: test.MyMojo
Conflicting implementation is: test.MyMojo'
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:213)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:51)

The configurations are below

MyMojo.java

import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugins.annotations.LifecyclePhase;
import org.apache.maven.plugins.annotations.Mojo;
import org.apache.maven.plugins.annotations.Parameter;

/**
 * Goal which validate the content.
 * @goal validate
 * @phase VERIFY
 */

@Mojo (name="validate", defaultPhase=LifecyclePhase.VERIFY, requiresProject=false )
public class MyMojo extends AbstractMojo
{
    @Parameter (property="message", defaultValue="Default Message")
    private String message;

    public void execute() throws MojoExecutionException
    {
        System.console().writer().println(message);
    }
}

Pom.xml

<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>test</artifactId>

  <packaging>maven-plugin</packaging>

  <version>1.0-SNAPSHOT</version>

  <name>test Maven Mojo</name>

  <url>http://maven.apache.org</url>

  

    <properties>

    <maven.compiler.source>1.8</maven.compiler.source>

    <maven.compiler.target>1.8</maven.compiler.target>

  </properties>

  

  <dependencies>

    <dependency>

      <groupId>org.apache.maven</groupId>

      <artifactId>maven-plugin-api</artifactId>

      <version>3.0</version>

    </dependency>

    <dependency>

      <groupId>junit</groupId>

      <artifactId>junit</artifactId>

      <version>3.8.1</version>

      <scope>test</scope>

    </dependency>

  <dependency>

      <groupId>org.apache.maven.plugin-tools</groupId>

      <artifactId>maven-plugin-annotations</artifactId>

      <version>3.4</version>

      <scope>provided</scope>

    </dependency>

    <dependency>

      <groupId>org.apache.maven</groupId>

      <artifactId>maven-core</artifactId>

      <version>3.2.5</version>

      <scope>provided</scope>

    </dependency>

  </dependencies>

</project>

After analysis, the root cause is @goal validate in the Java annotation and the @Mojo setting (name="validate") generating the same goal - validate and failing with the duplicate exception.

/**
 * Goal which validate the content.
 * @goal validate
 * @phase VERIFY
 */

@Mojo (name="validate", defaultPhase=LifecyclePhase.VERIFY, requiresProject=false )

The deployment is success after removing the @goal validate from the java annotation.

import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugins.annotations.LifecyclePhase;
import org.apache.maven.plugins.annotations.Mojo;
import org.apache.maven.plugins.annotations.Parameter;

/**
 * Goal which validate the content.
 * @phase VERIFY
 */

@Mojo (name="validate", defaultPhase=LifecyclePhase.VERIFY, requiresProject=false )
public class MyMojo extends AbstractMojo
{
    @Parameter (property="message", defaultValue="Default Message")
    private String message;

    public void execute() throws MojoExecutionException
    {
        System.console().writer().println(message);
    }
}