First, thank you for your answer!
Secondly, I have in my
jsp :
Since I use the tag <s:fielderror>,
Struts 2 checks that what you enter in the field is of the same type as the attribute in the action.
In my action, the attribute "duree" is a BigDecimal.
So, if I enter "yyy" for example in my field "duree", the message "invalid field value" appears even if I haven't a field-validator in my xml file.
It's why I say that the validation of the field's type is made automatically.
My problem is when I enter an invalid value, my attribute stays "null" and also, the message "duree is required" appears too, and I wish have only
the message "invalid field value".