public class IndexForm extends ActionForm {
  private int[] selectedPersons={5,6,7};
  
  private Person[] persons = null;

  public IndexForm() {
    Person p1 = new Person();
    p1.setId(5);
    
    Person p2 = new Person();
    p2.setId(7);
    persons = new Person[] { p1, p2 };
  }
...
}

jsp:
<html:form action="/index.do">
<logic:iterate id="person" property="persons">
<html:multibox property="selectedPersons">
<bean:write name="person" property="id"/>
</html:multibox>
</logic:iterate>
</html:form>