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Intro to Google App Engine for Java and CFML Developers

At OpenCF Summit 2011 we were very lucky to have Chris Schalk from Google come present on Google App Engine. If you're not familiar with Google App Engine (GAE) you should be! It's an absolutely fantastic application platform as a service offering from Google with great functionality, very slick features, and incredibly generous quotas for free application hosting. And if you need to go beyond these quotas, you simply configure billing and pay nominal fees for what you use over the free quotas.

GAE lets you deploy Python and Java applications, but one of the most interesting things going on with Java these days is the numerous different languages that run on the JVM. The Java platform being available on GAE opens up some very cool options.

At OpenCF Summit I followed Chris's presentation with one specific to Open BlueDragon on Google App Engine (GAE). OpenBD is a Java-based CFML runtime engine that allows you to deploy CFML applications to any standard servlet container, and also allows you to deploy your CFML applications to GAE. This is a great option for CFML developers since it's a quick and easy--not to mention free for many apps!--way to get your CFML applications online without having to worry about setting up a server yourself or getting a hosting account. Not to mention that if you deploy your CFML apps on GAE you get the benefits of running on Google's infrastructure and have on-demand scalability for your apps.

If you're not familiar with CFML, it's an incredibly powerful dynamic scripting language and framework that runs on the JVM. Think of it as a Java Tag Library on steroids. Even if you choose to build the backend of your applications in Java, CFML is a fantastic view layer language that's a great alternative to JSP, it interacts seamlessly with Java code, and it makes a lot of things that are quite verbose in Java extremely quick and easy. Of course CFML is a full-fledged language as well so you can build entire applications in it quickly.

The tools available for GAE make it very easy to work with. If you use Eclipse, a great option is to grab the GAE plugin for Eclipse. This gives you the entire GAE environment that will run right inside Eclipse and let you develop and test locally. Then when you're ready to deploy to GAE, it's a right-click away.

We also have great tools for OpenBD. In addition to being able to grab the GAE edition of OpenBD and drop that into an Eclipse project, you can use the new OpenBD Desktop. This is a desktop application that runs on GNU/Linux, Mac, and Windows, and lets you set up a local development server in seconds. Once development is complete you can then deploy your CFML application to a standard JEE WAR, or you can deploy straight to GAE from OpenBD Desktop.


In this post I'm going to cover getting up and running with GAE in Eclipse, and in my next post I'll go over the demo application I built for my presentation at OpenCF Summit, and in that post I'll highlight some of the cool features not only of OpenBD for GAE but GAE itself.

I'm going to cover how to set things up in Eclipse in this blog post, but I'll have another how to and screencast covering OpenBD Desktop soon.

Installing the Google App Engine Plugin for Eclipse

I'm going to assume my audience is mostly Java or CFML developers who are already somewhat familiar with Eclipse, but if you need assistance with this piece of things please leave me a comment and I will be happy to help.

The GAE plugin for Eclipse installs in the same way as any other add-on for Eclipse. You simply open Eclipse, go to Help -> Install New Software and paste in the appropriate update site URL for your version of Eclipse. This will download everything you need to work with GAE from within Eclipse, including the GAE for Java SDK.

Once the plugin installs and you restart Eclipse, you'll notice new Google icons in your Eclipse toolbar:


As well as a new Google right-click menu:


To create a new GAE project, you go to File -> New -> Project, and in the Google folder choose Web Application Project.


You can then run your GAE application from within Eclipse by right-clicking the project and choosing Run As -> Web Application. Running in debug mode and all the other Java functionality with which you may be familiar is of course also available.

Note that because GAE is a platform as a service offering, the entirety of the Java world isn't necessarily available to you. If you're curious what is and isn't available check the JRE Class Whitelist in the GAE docs.

Installing Open BlueDragon for GAE

With a new GAE project created in Eclipse, installing OpenBD for GAE is as easy as downloading a zip file, unzipping, and copying files into your GAE project's war directory.

When you download and unzip OpenBD for GAE you'll see these contents:


If you're new to OpenBD for GAE you'll want to read the README files included.

To add OpenBD to your GAE project, go into the war directory in the unzipped OpenBD for GAE directory, and copy all the files in the OpenBD war directory into the war directory in your Eclipse GAE project. Note that you will overwrite any files with the same name in the Eclipse project, which is what you want to do.

What you do not want to do is delete all of the existing files in the war directory in the Eclipse project and have only the OpenBD GAE war files in the Ecliipse project. To put it another way, you are merging the OpenBD for GAE files with the files that are already in the Eclipse project, and any files with the same name will be replaced by the OpenBD for GAE files.

With these files in place, right-click on the project in Eclipse and choose Run As -> Web Application. You should see something similar to this in the Eclipse console:


You may see some warnings as well but these are typically harmless, and if you already have something running on port 8888 you'll want to shut that down before launching the OpenBD GAE application.

If everything started up successfully you can then navigate to http://localhost:8888 in a browser and see this:


You're now all set to build CFML applications for GAE!

Working with CFML Code

Working with CFML code in an OpenBD for GAE project is no different that typical CFML development. The only real thing you need to be aware of is that your CFML code must be placed in the war directory in your Eclipse project. This is the root of your application. (Note that if you haven't worked with CFML or perhaps use a CFML editor other than Eclipse, you'll want to install CFEclipse, which is a great open source CFML plugin for Eclipse.)

Let's add a CFML file to our project so you can get a feel for working with CFML code in the context of an OpenBD for GAE project.

In your Eclipse project right-click the war directory and choose New -> File and name the file test.cfm. In this newly created file, add the following code:

<cfset name = "Matt" /> <cfoutput>Hello #name#! Today is #DateFormat(Now())#.</cfoutput>

Save the file, and then go to http://localhost:8888/test.cfm in your browser. You should see this:


That's all there is to it. You can now build CFML applications as usual using OpenBD for GAE.

Up until recently there have been some differences in supported syntax and functionality between "regular" OpenBD and OpenBD for GAE, but as of the next release of OpenBD the regular Java edition and the GAE edition will have the same exact functionality available, other than where specific functionality is not allowed on the GAE platform. The current nightly builds of OpenBD are based on this new unified codebase between the two editions of OpenBD.

Most CFML code will work fine on OpenBD for GAE. For example, the Mach-II framework as well as ColdSpring both work perfectly, and these frameworks are being used for the open source Enlist application that we started developing during the hackfest at OpenCF Summit.

What's Next?

Probably the major thing developers will run into immediately when building apps for GAE is that a traditional relational database is not available other than through Google App Engine for Business. If you aren't on the GAE for Business platform, you'll be using the Google Datastore, which is a high-performance, highly scalable key-value ("NoSQL") datastore that can be accessed via JDO or JPA, and also in CFML via GAE-specific functionality built into OpenBD for GAE.

I'll cover the Google Datastore as well as some of the amazing features of the GAE platform (including receiving mail and receiving/sending XMPP messages) in my next post.


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