If you migrate applications from Grails 2 to Grails 3, one item in your migration checklist is the transformation of Grails 2 Filters into Grails 3 Interceptors. @puneetbhl introduces you to Interceptors and shows you how to migrate methods such as beforeInterceptor from your Grails 2 Controllers.
Great presentation by @jeffscottbrown and @starbuxman. They show first that you can develop Spring Boot applications with Groovy. And Groovy is a first-class citizen. Then, they move to create the similar app but with Grails 3. You will see some of the developer-productivity features which Grails brings to the game. Forward it to any Spring Developer.
GSPs are not just a fabulous view technology to generate HTML pages. They are also an excellent resource to render those pesky HTML emails. You will still use invisible tables :-( to format your emails but at least rendering a model against your HTML email templates will be easy.
@mrhaki shows how to render a GSP view or template form a Grails Service.