How can I set a default value if a user doesn't send an input in Thymeleaf

Question

Right now - I have a input field on my html that Thymeleaf sticks a '0' in when the page loads. If for some reason that '0' is erased and the form is submitted - I get a NumberFormatException.

Is there a way I can automatically make it '0' if the form is submitted without anything in the input form?

Here's my html form (my th:object is ${npf})

<div class="col-md-2 form-outline">
     <input class="form-control" type="text" id="addConcealed" th:field="${npf.numConcealed}" placeholder="C" />
     <label class="form-label text-muted" for="addConcealed">Concealed</label>
</div>

Here's the error I get:

[Failed to convert property value of type 'java.lang.String' to required type 'long' for property 'numConcealed'; nested exception is java.lang.NumberFormatException: For input string: ""]

Anyway I can have it default to 0 if there's nothing in the input field rather than erroring out and making the user enter a number?

Answer 1

There are a couple ways to handle this:

1. Turn your variable numConcealed into an Long instead of a long. Deal with a null value when they erase the field.

2. Use JavaScript, capture the submit just change the field value back to 0 if they submit a blank text field.

3. Create your own String to int Converter and register it for that field. Should work the same way as the normal converter (whatever that is) except it would return 0 for nulls.