I do a lot of work with both ratpack and dropwizard for SmartThings. Dropwizard has a lot more opinions than Ratpack does out of the box, but they’re opinions I’ve grown used to and that I mostly agree with. I wanted validation in Ratpack to work as similarly as it does in Dropwizard.

Requirements

Use JSR-303
Be (mostly) automatic. I didn’t want to add much code to each handler to validate and send the error response
Not use exceptions for flow control.

Solution

The solution is pretty simple and it uses the Promise.route method to short circuit the promise chain and call clientError(int statusCode) immediately. Here’s a complete example.

import org.apache.http.HttpStatus
import org.hibernate.validator.constraints.NotEmpty
import ratpack.exec.Promise
import ratpack.handling.Context
import ratpack.jackson.Jackson

import javax.validation.Validation
import javax.validation.Validator
import javax.validation.constraints.NotNull

import static ratpack.groovy.Groovy.ratpack

class Widget {
	@NotNull
	@NotEmpty
	String name
}

ratpack {
	bindings {
		bindInstance(Validator, Validation.buildDefaultValidatorFactory().validator)
	}

	handlers {
		post("widget") {
			parseAndValidate(context, Widget)
					.map(Jackson.&json)
					.then(context.&render)
		}
	}
}

private <T> Promise<T> parseAndValidate(Context ctx, Class<T> type) {
	return ctx.parse(Jackson.fromJson(type)).route({ T obj ->
		return (ctx.get(Validator).validate(obj).size() > 0)
	}, {
		ctx.clientError(HttpStatus.SC_UNPROCESSABLE_ENTITY)
	})
}

plugins {
    id 'io.ratpack.ratpack-groovy' version '1.3.3'
    id 'com.github.johnrengelman.shadow' version '1.2.3'
}
 
repositories {
    jcenter()
}
 
dependencies {
    compile 'org.hibernate:hibernate-validator:5.2.2.Final'
}

The parseAndValidate function parses the json just like you would normally o, then it calls the route method on promise and validates the the POGO using the Hibernate Validator. If there are any validation errors, route will short-circuit the promise chain and call clientError with a 422 status code.

This is solution is similar to the Mr. Haki article Ratpacked: Validating Forms: Validating Forms