What is GAE ( google app engine )?
1. GAE is a platform provided by google to develop and host your web application.
2. For that you need to develop your application in specific way suggested by GAE i.e. you need to use google datastore to store your data and also there are some limitations while developing the application etc.
3.Now GAE support only two languages JAVA and PYTHON.
4.For Java it provides a plugin for Eclipse IDE which makes development and deployment easier and faster.
5. For development and testing the application there is no restriction but for deployment of the application you need a google account which allow you to deploy maximum 10 application (which is free).
6. Once you deploy your application in GAE it is ready to serve to your users.
7.When you are using GAE in free there are some limitation or daily quota for using the resources of GAE i.e. CPU Time, no. of requests, Outgoing Bandwidth etc.
Why You Need GAE ?
1. If you have an application and you want to deploy it (so that it can serves to your users), basic thing is you need a web server, SQL database and operating systems etc.
2. When the deployment is over your task is not finished, you need to monitor your app, maintain traffic and also there is chance of hard disk failure, machine break etc.
3. As your application grows these things seems more complecated.
4. But with the help of GAE, you don’t have to worry about the above problems, all problems will be handled by GAE.
What GAE does ?
1.GAE does three main things :
a) Runs and serve your codes for you.
b) Apps runs on google infrastructure so your app take advantage of the same scaleable technologies that Google applications are built on.
c) Handle the entire life cycle of your app.
I have deployed a sample chat application (developed using java) as an example reference, use the below link
http://mfchatmfchat.appspot.com (Use FireFox for better view)