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6.1.13 Asynchronous Request Processing - Reference Documentation

Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith

Version: 2.0.4

6.1.13 Asynchronous Request Processing

Grails support asynchronous request processing as provided by the Servlet 3.0 specification. To enable the async features you need to set your servlet target version to 3.0 in BuildConfig.groovy:

grails.servlet.version = "3.0"

With that done ensure you do a clean re-compile as some async features are enabled at compile time.

With a Servlet target version of 3.0 you can only deploy on Servlet 3.0 containers such as Tomcat 7 and above.

Asynchronous Rendering

You can render content (templates, binary data etc.) in an asynchronous manner by calling the startAsync method which returns an instance of the Servlet 3.0 AsyncContext. Once you have a reference to the AsyncContext you can use Grails' regular render method to render content:

def index() {
    def ctx = startAsync()
    ctx.start {
        new Book(title:"The Stand").save()
        render template:"books", model:[books:Book.list()]
        ctx.complete()
    }
}

Note that you must call the complete() method to terminate the connection.

Resuming an Async Request

You resume processing of an async request (for example to delegate to view rendering) by using the dispatch method of the AsyncContext class:

def index() {
    def ctx = startAsync()
    ctx.start {
        // do working
        …
        // render view
        ctx.dispatch()
    }
}