Grails Goodness: Accessing Resources with Resource and ResourceLocator

Grails uses Spring and we can piggyback on the Spring support for resource loading to find for examples files in the classpath of our application. We can use the Spring org.springframework.core.io.Resource or org.springframework.core.io.ResourceLoader interface to find resources in our application.

And since Grails 2.0 we can also use the org.codehaus.groovy.grails.core.io.ResourceLocator interface. In our code we can use the grailsResourceLocator service which implements the ResourceLocator interface. We must inject the grailsResourceLocator service into our code and we use the method findResourceForURI(String) to find a resource. The advantage of the grailsResourceLocator service is that it knows about a Grails application. For example resources in plugins can also be accessed.

First we look at a sample Grails service with a Resource property with the name template. In our code we get the actual resource using the getURL() method. The value of the Resource property we set in grails-app/conf/Config.groovy. We rely on the automatic conversion of properties of Spring so we can use a value like classpath:filename.txt and it will be converted to a Resource implementation.

package com.mrhaki.templates

import groovy.text.SimpleTemplateEngine
import org.springframework.core.io.Resource

class MessageService {

    Resource template

    String followUpMessage(final String user, final String subject) {
        final Map binding = [user: user, subject: subject]
        final SimpleTemplateEngine templateEngine = new SimpleTemplateEngine()
        templateEngine.createTemplate(template.URL).make(binding)
    }
}

In grails-app/conf/Config.groovy we define:

...
beans {
    messageService {
        template = 'classpath:/com/mrhaki/templates/mail.template'
    }
}
...

If we use the grailsResourceLocator we get the following service implementation:

package com.mrhaki.templates

import groovy.text.SimpleTemplateEngine

class MessageService {

    def grailsResourceLocator

    String template

    String followUpMessage(final String user, final String subject) {
        final Resource template = grailsResourceLocator.findResourceForURI(template)
        final Map binding = [user: user, subject: subject]
        final SimpleTemplateEngine templateEngine = new SimpleTemplateEngine()
        templateEngine.createTemplate(template.URL).make(binding)
    }
}

Code written with Grails 2.2.4