Let’s say you have two services named UserService and both are included in your Grails classpath. This can happen, for example if you have a “core” package, and an “application” package that extends services from “core”.

Here’s what that might look like in our case:

Well, if you try to use “UserService” in your Grails application like so, you will get an error saying that UserService cannot be found.

    def userService

That’s because there was a name collision on UserService.

Spring accounts for this, and allows you to define your class for each bean name. In Grails, we can define our beans in the grails-app/conf/resources.groovy file.

Here’s an example of what our resources.groovy file would look like:

beans = {
  // syntax is beanId(implementingClassName) { properties }
  // User Service
  coreUserService(com.company.core.UserService) {
    grailsApplication = ref("grailsApplication")
  }
  userService(com.company.usecase.UserService) {
    coreUserService = ref("coreUserService")
  }
}

Then, in your services, you can inject these services like so:

class UserController {
  def userService

  ...
}

// From your UserService, you can access the core UserService like this.
package com.company.core.UserService
class UserService {
  def coreUserService

  ...
}

Hopefully, that helps.