Introduction to App Engine - Beginning Java Google App Engine - page 22

The Memcache service is covered in Chapter 8, but here are a few more details on
how the measurements are calculated.

• Memcache API Calls : Total number of times the application

accessed the Memcache service to get, set, or expire values.

• Data Sent to / Received from API : The total amount of data sent to

and from the Memcache service.

Components of an App Engine Application
Building scalable applications with Google App Engine for Java (GAE/J) is similar to
building Java applications in your typical on-premise environment with one large
exception: there's no need for the network, hardware, operating system, database, or
application-server layers of the stack! With Google App Engine for Java, and Platform as a
Service offerings in general, you can start to innovate and develop on your application
right away and forget about the laborious tasks like setting up the OS and configuring the
database. Google App Engine for Java provides a Java 6 JVM and a Java Servlet interface,
and supports standard Java technologies like JDO, JPA, JavaMail, and JCache. Google App
Engine for Java applications can be developed using the Eclipse IDE, and the Google
Plugin for Eclipse even provides a local development server and deployment tools when
you're ready to go live with your App Engine application.
There are a few standard components to any Google App Engine for Java application.
Some of these are optional if you're using other technologies in their place. For example,
the Users service is a great way to provide a trusted authentication mechanism to your
user base. But, if you're developing a Facebook application on the App Engine platform,
you might be using Facebook Connect from Facebook's native authentication services,
in which case the Users service might not be relevant. Table 2-10 gives you a quick look at
the basic core components of a standard Google App Engine application.

Table 2-10. Standard App Engine Technology Stack

GAE / J service Description

JRE Google App Engine for Java provides a standard Java 6 JVM and

supports Java 5 and later. It also uses the Java Servlet standard, which
allows you to serve JSP pages and standard files.

Datastore Google App Engine for Java provides a persistent, scalable, fast

datastore built on the DataNucleus Access Platform. You can use JDO
and JPA to interact with the datastore and leverage the Memcache API
for transient distributed storage for queries results and calculations.