The problem you are experiencing is true for any Java/Web
framework. An HTTP request parameter does not understand
what a Java null is but always uses the empty string "". So
somewhere in your application (or framework) you have to
handle the conversion from "" to null.
When it comes to String values, null is not the same as ""
so I would recommend that your backing beans be populated
with "" instead of null when dealing with JSF. Alternatively,
you could create a NullStringConverter which converts from
"" to null.
When it comes to non-String values, then your converter should
return null from the getAsObject method when an "" is the
request parameter.
-Bryan
vlad10 wrote:
I'm fresh with JSF,
just started building some prototypes with facelets 1.1.11, myfaces
1.1.3/tomahawk 1.1.3.
I'm getting this general feeling that the framework is missing some
important feature.
I may create an inputText and populate it with a null value, the framework
conviniently will convert it into an empty string and populate my page.
However, on submit the valueChangeListener will fire with the reason that
null is not the same as an empty string.
I have another example. This the initial value is not null. I may explicitly
add a converter to that field, so the value stored in POJO as jva.util.Date
or as a BigDecimal or anything else will be nicely displayed on the screen,
but I'll face again the unwanted behavior of my valueChangeListener.
For the time being, I'm trying to compensate this deficiency in my app by
adding some filtering in a utility class. At the moment it's in the
beginning, just checking null/empty string case:
/**
* UIInput value is never null when submitted, but the POJO is always
* initialized with nulls. This creates a false alarm by
valueChangeListeners.
* This method tries to compensate this deficiency.
* @param input
* @param rec
* @return
*/
public static boolean isValueChanged(UIInput input, Object pojo) {
String name = input.getId();
Object val = BeanUtil.getBeanValue(pojo,name);
if (val == null)
if(StringUtils.isEmpty(input.getValue().toString()))
return false;
else
return true;
return (input.getValue().toString().compareTo(val.toString()) != 0);
}
My question: am I missing something????
Do I really need to add another layer in my app, I may call it something
like JSF Frendly POJOs. I may perform all necessary conversions right there
when moving data from DB to the screen, and then on submit perform the
opposit conversion when moving data back. I hope I can avoid that.
Is not it possible for a framework to 'remember' not just an oldValue, but
also the conversion performed, so prior to comparing old/new values it would
apply that same converter to the old value???
I think, this part has been missed.
thanks
vlad
