In the case of a multi-valued enumeration attribute like otherAvailableLanguages or publicationForms, the Retrieve/List All view must show a value in the form of a comma-separated list, like "English, German, Spanish", as shown in the following table:

For this purpose, we define a method that creates the desired serialization of a multi-valued attribute and use it in the code of the facelet file retrieveAndListAll.xhtml from WebContent/views/books/. For the publicationForms attribute, the method code is as follows:

public String getPublicationFormsValues() {
  String result = "";
  if (this.publicationForms != null) {
    int i=0, n = this.publicationForms.size();
    for (PublicationFormEL pf : this.publicationForms) {
      result += pf.name().toLowerCase();
      if (i < n-1) result += ", ";
      i++;
    }
  }
  return result;
}

Notice that in the case of the publicationForms attribute, the underlying enumeration PublicationFormEL does not have a label property. Instead, we use the enumeration literal name in lowercase as the label.