Programming with Java on Google App Engine

I wrote a draft post about Google App Engine many moons ago when it was Python only. As I’m not a Python man, the post isn’t very technical. Anyway, things have changed and GAE now supports Java. Albeit a customized subset of Java, which I’ll go into later.

Google App Engine is a cloud computing service: run your programs on their servers and pay by CPU usage. It’s similar to Amazon’s EC2 and Microsoft’s Azure, but unlike them in there is an absolutely free trial. You’re only required to provide a telephone number when signing up.

Step 1: Create the proper account

Sign up for a Google account here and a Google App Engine account here. After the GAE account is created, you should be prompted to create a new Google App Engine ID.

Now, if you’re like me, I won’t want to have to download and install the various SDKs and IDE to make your GAE app. So, I suggest Codenvy. Be sure your logged in to your Google account and click “Connect with Google”. Be sure you’re not using Internet Explorer, Codenvy seems to have issues with it.

Step 2: Create a project

On the welcome screen, choose “Create a New Project From Scratch”

Choose  Java Web Application (WAR) -> Google App Engine

You have to select the sample project, but you can skip using the JRebel plugin.

Use the Google App Engine ID you just created.

Step 3: Clear out the sample code

Click the project tab in the left menu (next to the Package Explorer tab)

Delete the src\main\java\com folder.

Delete the src\main\webapp\display.jsp file.

Open src\main\webapp\WEB-INF\web.xml and empty the “servlet” and “servlet-mapping” items. You can add java code to the src\main\java folder at a later time and add the proper information in these tags to specify it as a servlet.

Add the following in the “web-app” item after the “servlet-mapping” item:

<welcome-file-list>

        <welcome-file>index.jsp</welcome-file>

 </welcome-file-list>

Open src\main\webapp\WEB-INF\appengine-web.xml and make sure the “application” has enclosed your Google App Engine ID

 Customize src\main\webapp\index.jsp as you wish.

Step 4: Run your app on Codenvy servers

Make sure you save! Codenvy does not auto save changes when building.

Run -> Run Application

Step 5: Load your app into Google App Engine:

Make sure you save! Again, Codenvy does not auto save changes when building.

Go to Project -> PaaS -> Google App Engine

Select Application Update

If you get an Oath token error:

PaaS -> Google App Engine -> Logout

PaaS -> Google App Engine -> Login

Also, see this link for setting up cron jobs.