URL Mappings

URL Mappings Configuration

URL mappings in Grails define how URLs map to controller actions. They are configured in grails-app/controllers/.../UrlMappings.groovy and provide a powerful way to customize routing.

Basic Mappings

class UrlMappings {
    static mappings = {
        "/"(controller: "home", action: "index")
        "/book/$id"(controller: "book", action: "show")
        "/books"(controller: "book", action: "list")
    }
}

Dynamic Path Variables

You can capture URL segments as parameters using the dollar sign syntax:

"/book/$id"(controller: "book", action: "show")

// Multiple segments
"/author/$authorId/book/$bookId"(controller: "book", action: "showByAuthor")

Constraints and Filters

URL mappings support constraints to restrict which URLs are matched:

"/book/$id"(controller: "book", action: "show") {
    constraints {
        id matches: /[0-9]+/
    }
}

RESTful Mappings

Grails provides shorthand methods for RESTful routes:

resources "book"

This single line creates mappings for index, show, create, update, and delete actions following REST conventions.

Error Handling

The 404 and 500 mappings handle pages not found and server errors respectively:

"404"(controller: "errors", action: "notFound")
"500"(controller: "errors", action: "serverError")

Key Points

• URL mappings are defined in UrlMappings.groovy.
• Use dollar sign syntax for dynamic path variables.
• Constraints restrict URL matching patterns.
• resources creates RESTful route shorthands.
• Custom error pages handle 404 and 500 responses.