Describes the Google App Engine for Java.

1. Google App Engine
Anil Saldhana

2. Important Stuff To Remember
Use an IDE such as Eclipse and the Google App Engine
Plugin.
Take a look at the JRE White List to see the API that is
supported.
Run the application in local mode first before deploying in
the app engine.
App Engine in local mode : http://localhost:8888/_ah/admin
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3. Google App Engine Project
Install the Google Eclipse Plugin
Click on the "New Web Application Project" icon
Project Name: cjug, Package: cjug
Uncheck "Use Google Web Toolkit"
Retain the check on "Use Google App Engine"
Thats it.
You get a full fledged web application that you can run
on GAE.
HelloWorld Servlet.
web.xml declaring the servlet
index.html
appengine-web.xml
WEB-INF/logging.properties
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4. Configuration for GAE
Deployment Descriptor : web.xml
AppEngine DD: appengine-web.xml
Datastore Indexes : datastore-indexes.xml
Task Queues : queues.xml
Scheduled Jobs : cron.xml
DOS Protection: dos.xml
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5. Configuration : appengine-web.xml
The main configuration file for your web application.
Define your application id (<application>)
Define your application version (<version>)
Define your system properties
Define your static and resource files
(formats/includes/excludes)
Mandate SSL (<ssl-enabled/>)
Enable sessions (GAE uses datastore and memcache)
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6. Configuration : datastore-indexes.xml
The GAE uses indexes on queries made by applications.
You can predefine your queries and indexes.
<?xml version="1.0" encoding="utf-8"?>
<datastore-indexes
autoGenerate="true">
<datastore-index kind="Employee" ancestor="false">
<property name="lastName" direction="asc" />
<property name="hireDate" direction="desc" />
</datastore-index>
<datastore-index kind="Project" ancestor="false">
<property name="dueDate" direction="asc" />
</datastore-index>
</datastore-indexes>
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7. Configuration: Cron based scheduler
cron.xml in WEB-INF directory
<?xml version="1.0" encoding="UTF-8"?>
<cronentries>
<cron>
<url>/recache</url>
<description>Repopulate the cache every 2 minutes</description>
<schedule>every 2 minutes</schedule>
</cron>
<cron>
<url>/weeklyreport</url>
<description>Mail out a weekly report</description>
<schedule>every monday 08:30</schedule>
<timezone>America/New_York</timezone>
</cron>
</cronentries>
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8. Configuration: Task Queues
You can use QueueFactory.getDefaultQueue() or
Have a queue.xml in your WEB-INF directory
Without uploading entire app, you can update config
./appengine-java-sdk/bin/appcfg.sh update_queues
myapp/war
<queue-entries>
<queue>
<name>default</name>
<rate>1/s</rate>
</queue>
<queue>
<name>mail-queue</name>
<rate>2000/d</rate>
<bucket-size>10</bucket-size>
</queue>
<queue>
<name>background-processing</name>
<rate>5/s</rate>
</queue>
</queue-entries>
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9. Configuration : DOS Protection
dos.xml in WEB-INF directory
<?xml version="1.0" encoding="UTF-8"?>
<blacklistentries>
<blacklist>
<subnet>1.2.3.4</subnet> <description>a single IP address</description> </blacklist>
<blacklist>
<subnet>1.2.3.4/24</subnet> <description>an IPv4 subnet</description>
</blacklist>
<blacklist>
<subnet>abcd::123:4567</subnet> <description>an IPv6 address</description>
</blacklist>
<blacklist>
<subnet>abcd::123:4567/48</subnet> <description>an IPv6 subnet</description>
</blacklist>
</blacklistentries>
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10. Other Services
Google Users Service
Integrate with Google user accounts.
Memcache
Distributed in-memory cache
Can either use JCache (JSR107) API or Low Level API.
URL Fetch API
Applications interact with other hosts on the internet
using http or https with this API.
java.net.URLConnection is supported
No persistent HTTP Connections
No explicit connection time outs.
Mail Services
Java Mail or Low Level API
Send and receive emails.
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11. Other Services
XMPP Services
Application can get XMPP messages from GTalk/Jabber
BlobStore API
Service large data objects (50MB limit)
Billing required to be enabled
Experimental
Eg: Application users want to upload a file. An opaque
blobstore key is returned.
Images Java API
API to deal with images - resize, crop etc
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12. For More Information
Online Documentation
Google Discussion Group
http://code.google.com/appengine/community.html
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