Bind empty String as null in Spring Boot

When a form is submitted with an input field without any data, the browser submits it as an empty string "". That's why Spring Boot writes this to the data object exactly this way - with a StringTrimmerEditor configuration in place, we can bind the value as null instead.

@ControllerAdvice
public class ControllerConfig {

    @InitBinder
    void initBinder(final WebDataBinder binder) {
        binder.registerCustomEditor(String.class, new StringTrimmerEditor(true));
    }

}

▴ Configuration to convert empty Strings to null

The above ControllerAdvice adds a new editor to our WebDataBinder. StringTrimmerEditor first removes all spaces at the beginning and end of the submitted form data (trim) - this is usually just an incorrect input from the user. With the parameter true empty Strings will also be converted to null.

This saves us from handling different cases separately and allows us to persist the data directly into the database, where we prefer to store a null value when no information was provided.

Bootify is a tool to intialize Spring Boot applications with its own database schema, an optional Thymeleaf frontend with CRUD functionalities and many more features on top - online in the browser without registration. When a frontend is selected, the StringTrimmerEditor is also provided exactly as described above.

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