Spring binding - dealing with numeric inputs? - forms

Question

I'm dealing with a Webflow application where I may have to submit the current form in order to delete a child record (complex workflow, sorry).
The problem is that if the user enters junk data into the form and then presses the "delete" button, the binding and/or validation will fail and the form will never be submitted.
Hence, if they enter junk data, they cannot delete the record.
What is the preferred way of dealing with users entering "junk" data in web forms, particularly entering non-numeric data in numeric fields? I have a Spring form backing object that looks like this:
public class MyFormInfo implements Serializable {
private String myName;
private Integer myNumber;
}
If the user enters junk in the myName field I can ignore that during validation. However if they enter junk in the myNumber field and the binding fails, I have no good way to trap that and I can't submit the form.
Anybody have a good way to deal with this?

Answer 1

Have a look at this answer as well, but in summary there is no good way to add an error message in the case of type mismatch at conversion time.
The mechanisms available (property editors, converters, bean validation) are not meant to deal with a type mismatch.
The best solution is probably to do the validation on the client side via Javascript via some field mask that only accepts numerics. Then on the server a type mismatch would only occur in case of a bug, so the unhandled error could be acceptable.
For doing this on the server, it's possible to add a String property to the DTO, and apply a bean validation:
#Pattern(regexp = "{A-Za-z0-9}*")
String numericField;
Then via bean validation is possible to add error messages to the page, see this example.

Answer 2

If you want to avoid decimal number input in Integer fields, you can do it like this:
In the HTML-form you can do:
<div class="form-outline">
<input type="number" min=1 max=100 required/>
</div>
In the Java-Form you can do:
#NotNull
#Max(value = 100)
#Min(value = 1)
#NumberFormat
private Integer countOfRooms = null;