Very useful example to set the System Component field in an issue using Groovy in a PostFunction.
import com.atlassian.jira.component.ComponentAccessor import com.atlassian.jira.issue.Issue import com.atlassian.jira.issue.MutableIssue import com.atlassian.jira.project.Project MutableIssue issue2 = issue Project project = issue.getProjectObject() def component = ComponentAccessor.getProjectComponentManager().findByComponentName(project.getId(),"Name of the component to set") issue2.setComponent([component])