Conversion Error setting value for 'null Converter' - Why do I need a Converter in JSF?

Question

I have problems understanding how to use selection in JSF 2 with POJO/entity effectively. For example, I\'m trying to select a Warehouse entity via the below dr

Answer 1

Example of JSF generic converter with ABaseEntity and identifier:

ABaseEntity.java

public abstract class ABaseEntity implements Serializable {

    private static final long serialVersionUID = 1L;

    public abstract Long getIdentifier();
}

SelectItemToEntityConverter.java

@FacesConverter(value = "SelectItemToEntityConverter")
public class SelectItemToEntityConverter implements Converter {

    @Override
    public Object getAsObject(FacesContext ctx, UIComponent comp, String value) {
        Object o = null;
        if (!(value == null || value.isEmpty())) {
            o = this.getSelectedItemAsEntity(comp, value);
        }
        return o;
    }

    @Override
    public String getAsString(FacesContext ctx, UIComponent comp, Object value) {
        String s = "";
        if (value != null) {
            s = ((ABaseEntity) value).getIdentifier().toString();
        }
        return s;
    }

    private ABaseEntity getSelectedItemAsEntity(UIComponent comp, String value) {
        ABaseEntity item = null;

        List selectItems = null;
        for (UIComponent uic : comp.getChildren()) {
            if (uic instanceof UISelectItems) {
                Long itemId = Long.valueOf(value);
                selectItems = (List) ((UISelectItems) uic).getValue();

                if (itemId != null && selectItems != null && !selectItems.isEmpty()) {
                    Predicate predicate = i -> i.getIdentifier().equals(itemId);
                    item = selectItems.stream().filter(predicate).findFirst().orElse(null);
                }
            }
        }

        return item;
    }
}

And usage: