Migrate from resources plugin to asset-pipeline

12 Sep 2016

Tags: Grails, Plugins


Since Grails 2.4.0 asset-pipeline has been the default plugin recommended to manage the static resources in a Grails application. In earlier versions of Grails the resources plugin was an option but with Grails 3 the only viable option is using asset-pipeline because resources is not available in Grails 3. If you want to know how to migrate from resources to asset-pipeline, this post is for you.

Let’s migrate!

I recommend you start the migration analyzing your layouts because probably those files contain most of your static resources (javascripts and css files). Imagine that the content of your main.gsp layout is the following:

<link rel="stylesheet" href="${resource(dir: 'assets/css', file:'bootstrap.min.css') }" />
<link rel="stylesheet" href="${resource(dir: 'assets/css', file:'jquery-ui-1.10.3.full.min.css') }" />
<link rel="stylesheet" href="${resource(dir: 'assets/css', file:'jquery-ui-1.10.3.custom.min.css') }" />
<link rel="stylesheet" href="${resource(dir: 'assets/css', file:'jquery.gritter.css') }" />
<link rel="stylesheet" href="${resource(dir: 'assets/css', file:'ui.jqgrid.css') }" />

<script src="${resource(dir:'assets/js', file:'bootstrap.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery-2.0.3.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery-ui-1.10.3.custom.min.js') }"></script>
<script src="${resource(dir:'assets/js', file:'jquery-ui-1.10.3.full.min.js') }"></script>
<script src="${resource(dir:'assets/js', file:'jquery.mobile.custom.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery.slimscroll.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery.gritter.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery.hotkeys.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery.easy-pie-chart.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery.maskedinput.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery.dataTables.min.js')}"></script>
<script src="${resource(dir:'assets/js', file:'jquery.dataTables.bootstrap.js')}"></script>
<script src="${resource(dir:'assets/js/jqGrid', file:'jquery.jqGrid.min.js')}"></script>
<script src="${resource(dir:'assets/js/jqGrid/i18n', file:'grid.locale-en.js')}"></script>

As you can see there are a bunch of css and javascript files that are mostly related to jQuery but all of those files are on the same directory. When doing the migration we’re also going to reorganize the files in a better way.

By default asset-pipeline creates the directories images, javascripts and stylesheets under grails-app/assets directory. Any file you copy into those directories can be served by the plugin. The easy way would be to copy all of the css and javascript files to those directories and change the way we import the resources. For example, with the following directory structure:

├── javascripts
│   └── bootstrap.min.js
└── stylesheets
    └── bootstrap.min.css

You could replace the following code:

<!-- Using resources -->
<link rel="stylesheet" href="${resource(dir: 'assets/css', file:'bootstrap.min.css') }" />
<script src="${resource(dir:'assets/js', file:'bootstrap.min.js')}"></script>

With this one:

<!-- Using asset-pipeline -->
<asset:stylesheet src="bootstrap.min" />
<asset:javascript src="bootstrap.min" />

Please notice that you don’t need to include the .js or .css extension because asset-pipeline will add it when looking for the files in those directories.

As I said you could just copy all those files and create a lot of entries in your layout using asset:stylesheet and asset:javascript, but we can do it better.

Defining bundles

If you take a look at the content of the grails-app/assets directory created by default you can find the files application.js and aplication.css. Let’s take a look at the content of the application.css file:

* This is a manifest file that'll be compiled into application.css, which will include all the files
* listed below.
* Any CSS file within this directory can be referenced here using a relative path.
* You're free to add application-wide styles to this file and they'll appear at the top of the
* compiled file, but it's generally better to create a new file per style scope.
*= require bootstrap
*= require grails
*= require main
*= require mobile
*= require_self

We’re defining a bundle called application (the name of the file) that will contain bootstrap, grails, main and mobile stylesheet files. Starting with that we’re going to add the rest of the original files we were using with resources plugin:

*= require bootstrap.min
*= require jquery/css/jquery-ui-1.10.3.full.min
*= require jquery/css/jquery-ui-1.10.3.custom.min
*= require jquery/css/jquery.gritter
*= require jqGrid/ui.jqgrid

You can create arbitrary bundles of your js and css files defining files in the root of those directories and declaring the files you want to add to that bundle. Now we’re going the create a bundle for the javascript files:

// require bootstrap.min
//= require jquery/js/jquery-2.0.3.min
//= require jquery/js/jquery-ui-1.10.3.custom.min
//= require jquery/js/jquery-ui-1.10.3.full.min
//= require jquery/js/jquery.mobile.custom.min
//= require jquery/js/jquery.slimscroll.min
//= require jquery/js/jquery.gritter.min
//= require jquery/js/jquery.hotkeys.min
//= require jquery/js/jquery.easy-pie-chart.min
//= require jquery/js/jquery.maskedinput.min
//= require jquery/js/jquery.dataTables.min
//= require jquery/js/jquery.dataTables.bootstrap

//= require jqGrid/jquery.jqGrid.min
//= require jqGrid/i18n/grid.locale-en

With these two bundles defined the only thing you need to do is replace all those javascript and stylesheet imports in your layout with the following lines:

<asset:stylesheet src="application" />
<asset:javascript src="application" />

Now we can run the application, open the inspector and see what happens:

All the javascript and css files are loaded in debug mode. This means that the resources won’t be optimized and you’ll have hot-reloading of the changes. This is the default behavior during development. For production all files will be minified and included in one file per bundle:

Organizing bundles

One last thing about organizing the bundles is that if we want to create our custom directories we need to create a top level directory in grails-app/assets and inside that directory we can create our arbitrary structure. I’ve named this directory libs but you can use the name you want:

├── javascripts
│   ├── application.js
│   └── bootstrap.min.js
├── libs
│   ├── jqGrid
│   │   ├── i18n
│   │   │   └── grid.locale-en.js
│   │   ├── jquery.jqGrid.min.js
│   │   └── ui.jqgrid.css
│   └── jquery
│       ├── css
│       │   ├── jquery.gritter.css
│       │   ├── jquery-ui-1.10.3.custom.min.css
│       │   └── jquery-ui-1.10.3.full.min.css
│       └── js
│           ├── jquery-2.0.3.min.js
│           ├── jquery.dataTables.bootstrap.js
│           ├── jquery.dataTables.min.js
│           ├── jquery.easy-pie-chart.min.js
│           ├── jquery.gritter.min.js
│           ├── jquery.hotkeys.min.js
│           ├── jquery.maskedinput.min.js
│           ├── jquery.mobile.custom.min.js
│           ├── jquery.slimscroll.min.js
│           ├── jquery-ui-1.10.3.custom.min.js
│           └── jquery-ui-1.10.3.full.min.js
└── stylesheets
    ├── application.css
    └── bootstrap.min.css

Effectively Asset Pipeline treats each of the subdirectories of grails-app/assets as another root for locating assets.


As you have seen in this post it’s pretty simple to organize the static resources using asset-pipeline plugin and migrate from resources.

If you want to take a closer look to the code, this example application is available here.

Published on 12 Sep 2016