PfOrderListConverter

import org.primefaces.component.orderlist.OrderList;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;
import java.util.List;
import java.util.Objects;

/**
 * Generic converter for primefaces component (orderList).
 * Fixes setting of lists with the correct Object values instead of Strings.
 * Without it, the setter of List<Object> sets as List<String> instead.
 *
 * NOTE: The converter is relying on object.hashCode() - mind the implications of a hash collision, 
 * you can override the corresponding object's hashCode() to account for that.
 *
 * @author dahoc
 */
public class PfOrderListConverter implements Converter
{
  @Override
  public String getAsString(FacesContext context, UIComponent component, Object entity)
  {
    if (entity == null)
      return "";
    return String.valueOf(entity.hashCode());
  }

  @Override
  public Object getAsObject(FacesContext context, UIComponent component, String uuid)
  {
    Object ret = null;
    if (uuid == null || uuid.equals(""))
      return null;

    if (component instanceof OrderList)
    {
      final OrderList orderList = (OrderList)component;
      if (orderList.getValue() == null)
        return null;

      final List componentEntries = (List)orderList.getValue();
      ret = retrieveObject(componentEntries, uuid);
    }

    return ret;
  }

  /**
   * Function retrieves the object by its hashCode.
   * Because this has to be generic, typing is raw - and therefore disable IDE warning.
   *
   * @param objects collection of arbitrary objects
   * @param uuid    hashCode of the object to retrieve
   * @return correct object with corresponding hashCode or null, if none found
   */
  @SuppressWarnings("unchecked")
  private Object retrieveObject(final List objects, final String uuid)
  {
    return objects
      .stream()
      .filter(Objects::nonNull)
      .filter(obj -> uuid.equals(String.valueOf(obj.hashCode())))
      .findFirst()
      .orElse(null);
  }
}