code: public File resolveArtifactToFile( Artifact artifact ) throws MojoExecutionException
      {
          final Artifact resolvedArtifact = resolveArtifact( artifact );
          final File jar = resolvedArtifact.getFile();
          if ( jar == null )
          {
              throw new MojoExecutionException( "Could not resolve artifact " + artifact.getId()
                      + ". Please install it with \"mvn install:install-file ...\" or deploy it to a repository "
                      + "with \"mvn deploy:deploy-file ...\"" );
          }
          return jar;
      }
docs: Attempts to resolve an {@link org.apache.maven.artifact.Artifact} to a {@link java.io.File}.
  
  @param artifact to resolve
  @return a {@link java.io.File} to the resolved artifact, never <code>null</code>.
  @throws org.apache.maven.plugin.MojoExecutionException if the artifact could not be resolved.