Form Handling in mangoo I/O

To access a submitted form in a controller class, you can pass the mangoo I/O Form class as a parameter. Example:

public Response index(Form form) {
    ...
}

The Form class provides convenient methods to retrieve form values:

public Response index(Form form) {
    File file = form.getFile();
    List<File> files = form.getFiles();
    String firstname = form.get("firstname");
    ...
}

Important Notes

• The Form class is only available for POST or PUT requests; otherwise, it will be null.
• The Form class is automatically accessible in templates without explicitly passing it.

Retaining Form Values After Redirects

By default, form values are not retained after a redirect. To persist form values across redirects, use:

form.keep();

This is useful when handling validation errors while maintaining previously entered values.

Form Validation

Consider the following form in a template:

<form action="/save" method="post">
    <input type="text" name="firstname" />
    <input type="text" name="lastname" />
    <input type="text" name="email" />
</form>

To validate the firstname and lastname fields, use the built-in validation functions:

public Response form(Form form) {
    form.expectEmail("email");
    form.expectValue("firstname");
    form.expectValue("lastname");

    if (form.isValid()) {
        // Handle form
    }
    return Response.ok().render();
}

The Form class allows checks for field existence, email validation, and more. Use hasErrors() to determine if the form is valid.

Built-in Validations

mangoo I/O provides various validation rules:

• Required
• Minimum length
• Maximum length
• Match (case-insensitive)
• Exact match (case-sensitive)
• Email format
• IPv4 format
• IPv6 format
• Range check
• Regular expressions
• Numeric values

Additionally, validations can be bound to a specific field to check values beyond form input:

• validateTrue
• validateFalse
• validateNull
• validateNotNull

These are useful for checking existing usernames or passing custom error messages to form fields.

Handling Form Errors

To display an error in a template, check for errors in a specific field:

<#if form.hasError("myField")>

This is useful for modifying CSS styles or displaying error messages when validation fails.

To retrieve a specific error message:

${form.getError("myField")}

For example, it may display:

Firstname cannot be blank

Customizing Error Messages

Error messages are defined in messages.properties (or language-specific message files). Default messages can be customized as follows:

validation.required={0} is required
validation.min={0} must be at least {1} characters
validation.max={0} can be a maximum of {1} characters
validation.exactMatch={0} must exactly match {1}
validation.match={0} must match {1}
validation.email={0} must be a valid email address
validation.ipv4={0} must be a valid IPv4 address
validation.ipv6={0} must be a valid IPv6 address
validation.range={0} must be between {1} and {2} characters
validation.url={0} must be a valid URL
validation.regex={0} is invalid
validation.numeric={0} must be a numeric value