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(Quick Reference) # beforeInterceptor ## Purpose Allows the interception of an action before it is executed. A `beforeInterceptor` can optionally halt execution of the action. ## Examples Simple tracing interceptor:
    def beforeInterceptor = {
        println "Tracing action ${actionUri}"
    }
A trivial security interceptor to implement login functionality:

    def beforeInterceptor = [action: this.&auth, except: 'login']// defined with private scope, so it's not considered an action
    private auth() {
        if (!session.user) {
            redirect(action: 'login')
            return false
        }
    }def login() {
        // display login page
    }
## Description The `beforeInterceptor` intercepts processing before the action is executed. If it returns `false` then the action will not be executed. The interceptor can be defined for all actions in a controller as follows:
    def beforeInterceptor = {
        println "Tracing action ${actionUri}"
    }
This declaration must be a class-scope Closure in the controller class. It will execute before all actions and does not interfere with processing since it returns no value. A common use case however is for simple authentication (although a security plugin is preferred):

    def beforeInterceptor = [action: this.&auth, except: 'login']// defined with private scope, so it's not considered an action
    private auth() {
        if (!session.user) {
            redirect(action: 'login')
            return false
        }
    }def login() {
        // display login page
    }
This defines a method called `auth`. It is declared as a private method so it is not exposed as a controller action. The `beforeInterceptor` then defines an interceptor that is used on all actions except the `login` action and is configured using Groovy's method pointer syntax to execute the `auth` method. The `auth` method will redirect to another page if it doesn't find a user in the session, and it signifies that it has handled the response and that the requested action should not be processed by returning `false`. This example limited the intercepted actions using the `except` argument but the `only` argument can also be used to list the actions to be intercepted, rather than those to not intercept. | Quick Reference (hide)