Before installing Grails 4.0.3 you will need as a minimum a Java Development Kit (JDK) installed version 1.8 or above. Download the appropriate JDK for your operating system, run the installer, and then set up an environment variable called JAVA_HOME pointing to the location of this installation.

To automate the installation of Grails we recommend SDKMAN which greatly simplifies installing and managing multiple Grails versions.

On some platforms (for example OS X) the Java installation is automatically detected. However in many cases you will want to manually configure the location of Java. For example, if you’re using bash or another variant of the Bourne Shell:

To create a Grails application you first need to familiarize yourself with the usage of the grails command which is used in the following manner:

Run create-app to create an application:

This will create a new directory inside the current one that contains the project. Navigate to this directory in your console:

Let’s now take the new project and turn it into the classic "Hello world!" example. First, change into the "helloworld" directory you just created and start the Grails interactive console:

You should see a prompt that looks like this:

What we want is a simple page that just prints the message "Hello World!" to the browser. In Grails, whenever you want a new page you just create a new controller action for it. Since we don’t yet have a controller, let’s create one now with the create-controller command:

Don’t forget that in the interactive console, we have auto-completion on command names. So you can type "cre" and then press <tab> to get a list of all create-* commands. Type a few more letters of the command name and then <tab> again to finish.

The above command will create a new controller in the grails-app/controllers/helloworld directory called HelloController.groovy. Why the extra helloworld directory? Because in Java land, it’s strongly recommended that all classes are placed into packages, so Grails defaults to the application name if you don’t provide one. The reference page for create-controller provides more detail on this.

We now have a controller so let’s add an action to generate the "Hello World!" page. In any text editor, edit the new controller — the HelloController.groovy file — by adding a render line. The edited file’s code should look like this:

The action is simply a method. In this particular case, it calls a special method provided by Grails to render the page.

Job done. To see your application in action, you just need to start up a server with another command called run-app:

This will start an embedded server on port 8080 that hosts your application. You should now be able to access your application at the URL http://localhost:8080/ - try it!

To set a context path for your application, you can add a configuration property in grails-app/conf/application.yml:

With the above configuration in place the server will instead startup at the URL http://localhost:8080/helloworld/.

Alternatively, you can also set the context path via the command line:

The result will look something like this:

This is the Grails intro page which is rendered by the grails-app/view/index.gsp file. It detects the presence of your controllers and provides links to them. You can click on the "HelloController" link to see our custom page containing the text "Hello World!". Voila! You have your first working Grails application.

One final thing: a controller can contain many actions, each of which corresponds to a different page (ignoring AJAX at this point). Each page is accessible via a unique URL that is composed from the controller name and the action name: /<appname>/<controller>/<action>. This means you can access the Hello World page via /helloworld/hello/index, where 'hello' is the controller name (remove the 'Controller' suffix from the class name and lower-case the first letter) and 'index' is the action name. But you can also access the page via the same URL without the action name: this is because 'index' is the default action. See the end of the controllers and actions section of the user guide to find out more on default actions.

Since 3.0, Grails has an interactive mode which makes command execution faster since the JVM doesn’t have to be restarted for each command. To use interactive mode simple type 'grails' from the root of any projects and use TAB completion to get a list of available commands. See the screenshot below for an example:

For more information on the capabilities of interactive mode refer to the section on Interactive Mode in the user guide.

Grails uses "convention over configuration" to configure itself. This typically means that the name and location of files is used instead of explicit configuration, hence you need to familiarize yourself with the directory structure provided by Grails.

Here is a breakdown and links to the relevant sections:

Grails applications can be run with the built in Tomcat server using the run-app command which will load a server on port 8080 by default:

You can specify a different port by using the -port argument:

Note that it is better to start up the application in interactive mode since a container restart is much quicker:

You can debug a grails app by simply right-clicking on the Application.groovy class in your IDE and choosing the appropriate action (since Grails 3).

Alternatively, you can run your app with the following command and then attach a remote debugger to it.

More information on the run-app command can be found in the reference guide.

The create-* commands in Grails automatically create unit or integration tests for you within the src/test/groovy directory. It is of course up to you to populate these tests with valid test logic, information on which can be found in the section on Unit and integration tests.

To execute tests you run the test-app command as follows:

Grails applications can be deployed in a number of different ways.

If you are deploying to a traditional container (Tomcat, Jetty etc.) you can create a Web Application Archive (WAR file), and Grails includes the war command for performing this task:

This will produce a WAR file under the build/libs directory which can then be deployed as per your container’s instructions.

Note that by default Grails will include an embeddable version of Tomcat inside the WAR file, this can cause problems if you deploy to a different version of Tomcat. If you don’t intend to use the embedded container then you should change the scope of the Tomcat dependencies to provided prior to deploying to your production container in build.gradle:

If you are building a WAR file to deploy on Tomcat 7 then in addition you will need to change the target Tomcat version in the build. Grails is built against Tomcat 8 APIs by default. To target a Tomcat 7 container, insert a line to build.gradle above the dependencies { } section:

Unlike most scripts which default to the development environment unless overridden, the war command runs in the production environment by default. You can override this like any script by specifying the environment name, for example:

If you prefer not to operate a separate Servlet container then you can simply run the Grails WAR file as a regular Java application. Example:

When deploying Grails you should always run your containers JVM with the -server option and with sufficient memory allocation. A good set of VM flags would be:

Grails runs on any container that supports Servlet 3.0 and above and is known to work on the following specific container products:

Some containers have bugs however, which in most cases can be worked around. A list of known deployment issues can be found on the Grails wiki.

In addition, reference the Grails Guides for tips on how to deploy Grails to various popular Cloud services.

Grails ships with a few convenience targets such as create-controller, create-domain-class and so on that will create controllers and different artefact types for you. NOTE: These are just for your convenience and you can just as easily use an IDE or your favourite text editor. For example to create the basis of an application you typically need a domain model:

This will result in the creation of a domain class at grails-app/domain/helloworld/Book.groovy such as:

There are many such create-* commands that can be explored in the command line reference guide.

To get started quickly with Grails it is often useful to use a feature called scaffolding to generate the skeleton of an application. To do this use one of the generate-* commands such as generate-all, which will generate a controller (and its unit test) and the associated views: