Spring @RequestParam custom type conversion

November 22, 2022

How do I create a custom type converter for a boolean parameter in a GET request?

For example, I want the allowed values in the GET request to be "oui" and "non" instead of "true" and "false". I followed the Spring documentation on how to do this, and tried the following:

@RestController
public class ExampleController {
    @InitBinder
    protected void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(Boolean.class, new CustomBooleanEditor("oui", "non", true));
    }

    @GetMapping("/e")
    ResponseEntity<String> showRequestParam(@RequestParam boolean flag) {
        return new ResponseEntity<>(String.valueOf(flag), HttpStatus.OK);
    }
}

I also tried this:

@RestController
public class DemoController {
    @InitBinder
    protected void initBinder(WebDataBinder binder) {
        binder.addCustomFormatter(new Formatter<Boolean>() {
            @Override
            public Boolean parse(String text, Locale locale) throws ParseException {
                if ("oui".equalsIgnoreCase(text)) return true;
                if ("non".equalsIgnoreCase(text)) return false;
                throw new ParseException("Invalid boolean parameter value '" + text + "'; please specify oui or non", 0);
            }

            @Override
            public String print(Boolean object, Locale locale) {
                return String.valueOf(object);
            }
        }, Boolean.class);
    }

    @GetMapping("/r")
    ResponseEntity<String> showRequestParam(@RequestParam(value = "param") boolean param) {
        return new ResponseEntity<>(String.valueOf(param), HttpStatus.OK);
    }
}

Neither of these worked. When supplying the value "oui", I got an HTTP 400 response with the following message:

Failed to convert value of type ‘java.lang.String’ to required type
‘boolean’; nested exception is java.lang.IllegalArgumentException:
Invalid boolean value [oui]"

Update:

I’ve also now tried using a Converter:

@Component
public class BooleanConverter implements Converter<String, Boolean> {
    @Override
    public Boolean convert(String text) {
        if ("oui".equalsIgnoreCase(text)) return true;
        if ("non".equalsIgnoreCase(text)) return false;
        throw new IllegalArgumentException("Invalid boolean parameter value '" + text + "'; please specify oui or non");
    }
}

This "kind of" works, in that it now accepts "oui" and "non", but it does so in addition to "true" and "false". How can I get it to accept "oui" and "non" instead of "true" and "false"?

>Solution :

In your first case, your requestParam is a boolean but you bind a Boolean.

I’ve tried with this code

@InitBinder
protected void initBinder(WebDataBinder binder) {
    binder.registerCustomEditor(Boolean.class, new CustomBooleanEditor("oui", "non", true));
}

@GetMapping("/e")
ResponseEntity<String> showRequestParam(@RequestParam(value="flag") Boolean flag) {
    return new ResponseEntity<>(String.valueOf(flag), HttpStatus.OK);
}

And it’s print