render

// renders text to response
render "some text"
// renders text for a specified content-type/encoding
render(text: "<xml>some xml</xml>", contentType: "text/xml", encoding: "UTF-8")
// render a template to the response for the specified model
def theShining = new Book(title: 'The Shining', author: 'Stephen King')
render(template: "book", model: [book: theShining])
// render each item in the collection using the specified template
render(template: "book", collection: [b1, b2, b3])
// render a template to the response for the specified bean
def theShining = new Book(title: 'The Shining', author: 'Stephen King')
render(template: "book", bean: theShining)
// render the view with the specified model
def theShining = new Book(title: 'The Shining', author: 'Stephen King')
render(view: "viewName", model: [book: theShining])
// render the view with the controller as the model
render(view: "viewName")
// render some markup to the response
render {
    div(id: "myDiv", "some text inside the div")
}
// render some XML markup to the response
render(contentType: "text/xml") {
    books {
         for (b in books) {
             book(title: b.title, author: b.author)
         }
    }
}
// render a JSON ( http://www.json.org ) response with the builder attribute:
render(contentType: "text/json") {
    book(title: b.title, author: b.author)
}
// render with status code
render(status: 503, text: 'Failed to update book ${b.id}')
// Automatic marshalling of XML and JSON
import grails.converters.*
…
render Book.list(params) as JSON
render Book.get(params.id) as XML