If we run our Grails 3 application in development mode our classes and GSP's are automatically recompiled if we change the source file. We change our source code, refresh the web browser and see the results of our new code. If we run our application with another environment, like production or a custom environment, then the reloading of classes is disabled. But sometimes we have a different environment, but still want to have hot reloading of our classes and GSP's. To enable this we must use the Java system property grails.reload.enabled and reconfigure the Gradle bootRun task to pass this system property.

Let's change our Gradle build file and pass the Java system property grails.reload.enabled to the bootRun task if it is set. We use the constant Environment.RELOAD_ENABLED to reference the Java system property.

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Ratpack is a lean library to build HTTP applications. Ratpack for example doesn't include functionality to validate forms that are submitted from a web page. To add form validation to our Ratpack application we must write our own implementation.

Let's write a simple application with a HTML form. We will use Hibernate Validator as a JSR 303 Bean Validation API implementation to validate the form fields. IN our application we also use the MarkupTemplateModule so we can use Groovy templates to generate HTML. We have a simple form with two fields: username and email. The username field is required and the email field needs to have a valid e-mail address. The following class uses annotations from Hibernate Validator to specify the constraints for these two fields:

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