Here’s a quick example how you can build a RESTfull Grails application and deploy it to Google App Engine. For this example you need Grails 1.1.1 and GAE SDK for Java version 1.2.1.
I’m going to create a small service which will return a wind forecast. The forecast data is hardcoded as this is just some sample data.
First create the grails application, remove the hibernate plugin, and install the app-engine plugin:
grails create-app windapp
cd windapp
grails uninstall-plugin hibernate
grails install-plugin app-engine
Make sure you’ve got your APPENGINE_HOME environment variable configured correctly. It should be something like:
export APPENGINE_HOME=/home/akoelewijn/programs/appengine-java-sdk-1.2.1
Next, I’ll create a controller which will implement a function to return the windforecast in JSON format:
grails create-controller Forecast
Edit the controller, and implement the method. The method just puts some dummy data into an array, which is returned as a JSON datastructure:
import grails.converters.*
class ForecastController {
def show = {
def forecast = []
forecast << [ windspeed: 5, winddirection: 200 ]
render forecast as JSON
}
}
Next, we need to edit the url mappings, calling the path /forecast will execute the method implemented above:
class UrlMappings {
static mappings = {
"/forecast"(controller:"forecast"){
action = [GET:"show"]
}
"/"(view:"/index")
"500"(view:'/error')
}
}
We have now implemented the service, which you can test, for example with curl. Test the application locally as follows:
grails app-engine run
curl http://localhost:8080/forecast
To test it on the google app engine, we first need to create an application. Log into Google app engine and create an application here: http://appengine.google.com/. For convenience, i’ve given it the same name as my grails application: windapp.
Now i can deploy the application:
grails set-version 1
grails app-engine package
$APPENGINE_HOME/bin/appcfg.sh update ./target/war
You should now have a running service. Again, we use curl to test it:
curl http://windapp.appspot.com/forecast
Now, using JQuery, i’ll create a simple html page to test the service. Create the webpage: web-app/index.html. To keep it simple, i’m using a google hosted version of jQuery, and i’m including all the javascript code in the page:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>Forecast service test</title>
<script type="text/javascript" src="http://www.google.com/jsapi"></script>
<script type="text/javascript">
google.load("jquery", "1");
google.setOnLoadCallback(function(){
$("#getForecast").click(getForecast);
});
function getForecast(){
$.ajax({
type:"GET",
url:"/forecast",
success:function(json){
$("#forecastResults").text("Wind speed: " + json[0]["windspeed"] +
", direction: " + json[0]["winddirection"]);
},
dataType: "json",
contentType: "text/json"
});
}
</script>
</head>
<body>
<h1>Forecast tester</h1>
<button id="getForecast">Get Forecast</button>
<div id="forecastResults"></div>
</body>
</html>
Redeploy the application to app engine:
grails app-engine deploy
Here’s the resulting page: windapp. Just push the button to call the REST service.
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