1. Building the Google Plugin for Eclipse
What We Learned
Presented by:
Rajeev Dayal
Originally Presented by:
Miguel Mendez
(at Eclipse Day 2009)
Google Confidential and Proprietary 1
Monday, April 25, 2011 1

2. Agenda
Background
Plugin Design Principles
Challenges, Solutions, and Lessons
GWT = Google Web Toolkit
GPE = Google Plugin for Eclipse
Google Confidential and Proprietary 2
Monday, April 25, 2011 2

3. Background
GPE, GWT, and App Engine
Google Confidential and Proprietary 3
Monday, April 25, 2011 3

4. What is the Google Plugin for Eclipse?
Collection of Eclipse plugins
Assists in the creation of Web Apps that use:
• Google Web Toolkit
• App Engine for Java
Google Confidential and Proprietary 4
Monday, April 25, 2011 4

5. What is the Google Web Toolkit?
Writing AJAX apps is hard
• JavaScript is a dynamically-typed language
• Each browser has its own quirks
What if you could write AJAX apps in Java?
• great tooling support (Eclipse!)
• autocompletion, refactoring
• first-class debugging
Enter GWT
• Debug your web app code in Eclipse while executing against a real browser
• Cross-compile your application into stand-alone, optimized JavaScript for
each browser
• Developers can still get to raw JavaScript via JavaScript Native Interface
(JSNI)
Google Confidential and Proprietary 5
Monday, April 25, 2011 5

6. What is App Engine?
App Engine is a cloud computing platform
• write a web app in Java (or Python) and deploy it
• lives at <app id>.appspot.com (or a custom domain)
We provide the container and services (Platform-as-a-Service)
• Hardware connectivity
• JVM
• Servlet Container
• Software services
• Automatic scaling
Your app is isolated from other running apps
• Sandboxing - restrict JVM permissions, whitelist JRE classes
• DevAppServer - local development server that emulates the production
environment Google Confidential and Proprietary 6
Monday, April 25, 2011 6

7. Plugin Design Principles
Google Confidential and Proprietary 7
Monday, April 25, 2011 7

8. Design Principles
Stability is paramount
Make it easy to get started
Reward sophisticated developers
Control is happiness
Keep things simple
Blend naturally into Eclipse
Developer’s time is valuable - help them maximize it
Minimize plugin magic
Google Confidential and Proprietary 8
Monday, April 25, 2011 8

9. Challenges, Solutions, and Lessons
Google Confidential and Proprietary 9
Monday, April 25, 2011 9

10. Installation
Challenge
• Don’t make the user download all of the pieces individually
• GPE is ready for use once installation completes
• People behind firewalls
Solution
• Bundle the App Engine and GWT SDKs as plugins
• Produce stand-alone archives for people behind firewalls
Lessons
• P2 garbage collection
 don’t solve this by burning the SDK version number into the plugin id :)
 make ‘SDK plugins’ non-singletons
• GPE has dependencies that are not in the standalone Eclipse distro -
producing archives to be placed in ‘archives’ is a bad idea
• Optional plugins - P2 is GREEDY Google Confidential and Proprietary 10
Monday, April 25, 2011 10

11. New Web Application
Challenge
• Quickly create web apps that use GWT and/or App Engine
• Use an exploded WAR layout
Solution
• Create a wizard that generates web apps that are ready-for-launch
• Allow users to select which versions of GWT/App Engine to use
• Use project natures to indicate what is being used, allow users to add GWT/
App Engine after the fact
• Manage SDK jars in the WEB-INF/lib folder
Lessons
• Not everyone wants sample code generated
• Did not make it easy to import GWT/App Engine samples
Google Confidential and Proprietary 11
Monday, April 25, 2011 11

12. Run/Debug Web Apps
Challenge
• Create a simple, customizable launch configuration
• Handle possible combinations of GWT & App Engine
• App Engine and GWT use different development servers
• Maximize transparency - users should be able to see additional program and
VM args
Solution
• Extend Java launch configurations and add some guiding UI
• Classpath provider to add source paths needed by GWT
• Launch configuration processors - keep program args and VM args in sync
with changes in the launch config settings in the UI
Google Confidential and Proprietary 12
Monday, April 25, 2011 12

13. Run/Debug Web Apps
Lessons
• Classpath modifications and reset are imperative
• Eclipse’s launch configuration infrastructure is not meant to handle the case
of one launch configuration tab affecting another
 there’s no consistent ‘model’ for all of the tabs
• Be careful when using performApply and updateLaunchConfigurationDialog
as a hook point for launch configuration processors
 slow launch configuration processors slow down the launch config UI
 launch configuration processors that rely on class lookups slow down in
proportion to the size of the classpath
• What do you do if the user modifies an argument that a launch configuration
processor is responsible for?
Google Confidential and Proprietary 13
Monday, April 25, 2011 13

14. SDKs
Challenge
• Plugin should support multiple versions of the App Engine and GWT SDKs
• Make it easy to switch versions
• Properly configure complex classpaths
Solution
• Classpath containers, e.g. JRE containers
• Classpath dialog and project properties enable trival SDK switching
Lessons
• Be careful what you do inside of ClasspathContainerInitializers
• Default SDK may not have been a great idea
• People ignore warnings in the problems view
• Classpath containers reduce project portability
• Implicit SDKs (especially Maven)
Google Confidential and Proprietary 14
Monday, April 25, 2011 14

15. GWT JSNI: Embed JavaScript in Java files
Challenge
• Embed JavaScript code in Java files
• GWT overloads native methods and Java block comment for JSNI
• Unfortunately, JSNI delimiters /*-{ }-*/ make JSNI blocks into multi-line
comments, and they get formatted as such
Solution
• Declare a new document partition for JSNI methods
• Color JSNI method bodies as JavaScript
• Fix up “formatting” performed by auto-format
Lessons
• Smokescreen pattern
• Redoing the formatting works, but alters undo stack
• Difference between code path for CTRL-SHIFT-F formatting and auto-format
on save Google Confidential and Proprietary 15
Monday, April 25, 2011 15

16. GWT JSNI: Refactoring, Search, and
Completion
Challenge
• JSNI uses JSNI-like signatures that are subject to typos and can invalidated
by refactoring
• Invisible to Java dependency and Java search
Solution
• Add completion proposals (based on Java completion proposals) to expand
JSNI refs
• Add validation (via a compilation participant) to check the validity of JSNI refs
• Participate in Java refactoring to update JSNI refs
• Participate in Java searches to include refs from JSNI
Lessons
• Indexing for speed
• “This method is not used” for JSNI refs to private methods
 @SuppressWarnings(“jsni”)
Google Confidential and Proprietary 16
Monday, April 25, 2011 16

17. GWT UiBinder - Validation
Challenge
• UiBinder files - .ui.xml - are associated with an “owner type”
• Validations need to be triggered on the owner type when the .ui.xml file is
changed, and vice versa
• The .ui.xml file can have references to other Java types - when those types
change, the .ui.xml file has to be re-validated
Solution
• compilation participant looks for Java file changes and triggers a validation
on associated .ui.xml files
 changes on the owner type
 changes in any type referenced by a .ui.xml file
• Use a IResourceChangeListener to trigger rebuilds on Java types referenced
by a .ui.xml file
Google Confidential and Proprietary 17
Monday, April 25, 2011 17

18. GWT UiBinder - Validation
Lessons
• Be very conservative when triggering rebuilds - workspace can be constantly
rebuilding if this is done incorrectly
• It would be nice if JDT could model dependencies between resources and
Java types
Google Confidential and Proprietary 18
Monday, April 25, 2011 18

19. App Engine JRE Whitelist
Challenge
• Inform developers when they’re using unsupported JRE APIs
Solution
• compilation participant
• Load whitelist out of App Engine SDK
• Provide quick-fixes to flag a class as not being used on the server side (a
GWT class)
Lessons
• Caching whitelist can be tricky because the underlying SDK can be changed
• Having the IDE change behavior based on the project’s classpath can be
confusing
Google Confidential and Proprietary 19
Monday, April 25, 2011 19

20. App Engine ORM
Challenge
• App Engine Datanucleus-based ORM uses bytecode enhancement
• Flag enhancement problems before the user runs the app
Solution
• Drive the Datanucleus enhancer as part of the build
• Provide ability to select which classes should be enhanced
Lessons
• Datanucleus wants to report errors to standard out
• Feedback via the console is less than optimal
• Want feedback as red squiggly in file
• Class file changes are what matter; not source file changes
• Do not let exceptions escape from your builders!
• Do not perform a refresh(...) in your builder - infinite build time :)
Google Confidential and Proprietary 20
Monday, April 25, 2011 20

21. Maven Support
Challenge
• Have GPE recognize a Maven project that uses GWT and/or App Engine as
an actual GWT/App Engine project
• Respect the GWT/App Engine SDK that Maven has configured
Solution
• Integrate with m2Eclipse to apply the App Engine/GWT Nature to a project
on the import of a Maven project (and download any needed artifacts)
• Prevent users from switching SDKs on a Maven project, and “synthesize” a
GWT/App Engine SDK for Maven projects based on the build path
Lessons
• Maven breaks up the canonical SDK and renames its jars
• Build classpath != launch classpath (Maven is VERY specific about this)
• Sometimes the jars that you need for launch have not been downloaded from
Maven central!
Google Confidential and Proprietary 21
Monday, April 25, 2011 21

22. Compilation Participants and ASTs
Challenge
• Need to perform fine-grained validation on Java files
 for UiBinder, RPC, JSNI, App Engine JRE)
Solution
• Use compilation participants to give you access to the Java AST as the user
types (reconcile()), and as a pre-build hook on the Java Builder
• Create ASTs from compilation units in buildStarting()
Lessons
• Compilation participants do not have access to the compile-time AST
• Resolving type bindings in an AST takes a long time and takes up lots of
memory; proportional to your classpath and source size
 use ASTBatchParser to speed things up
• compilation participants must complete before the Java Build can complete
• penalty for full rebuilds (from a type rename, classpath change)
Google Confidential and Proprietary 22
Monday, April 25, 2011 22

23. Other Challenges
GWT RPC support
• paired interfaces that need to be kept in sync
• interfaces do not have a common ancestor type
• refactoring is tricky - we need to perform the rename of the paired type after
JDT’s real refactoring
GWT CSS support
• static “extensions” to CSS
• need to modify WTP’s parser for the XML editor to understand GWT’s CSS
constructs
• generated a new CSS tokenizer from .flex rules
• formatter would corrupt CSS constructs that it was not aware of; had to
replace these with known constructs, allow the formatting to take place, and
then put the originals back
Google Confidential and Proprietary 23
Monday, April 25, 2011 23

24. Other Challenges
The Google Build System
• specific rules about how GWT and App Engine projects are built and pull in
dependencies
• the assumptions that we make about project and SDK structure do not hold
• parallels to the problems with Maven (sdks, build classpath != launch
classpath)
Development Mode View
• shows information about active GWT sessions
• server information is displayed to the console; console fights with
development mode view for focus
• which perspective do you contribute to?
Deploy to Google
• saving credentials - secure storage may prompt you for a password :(
• having GWT participate in the compile
Google Confidential and Proprietary 24
Monday, April 25, 2011 24

25. Questions
? ?
?
?
Google Confidential and Proprietary 25
Monday, April 25, 2011 25

26. Thank You
Documentation
 http://code.google.com/eclipse
Update sites
 Eclipse 3.6 (Helios) - http://dl.google.com/eclipse/plugin/3.6
 Eclipse 3.5 (Galileo) - http://dl.google.com/eclipse/plugin/3.5
 Eclipse 3.4 (Ganymede) - http://dl.google.com/eclipse/plugin/3.4
Google Web Toolkit and general GPE Feedback
 Group - http://groups.google.com/group/Google-Web-Toolkit
 Issue Tracker - http://code.google.com/p/google-web-toolkit/issues
App Engine Feedback
 Group - http://groups.google.com/group/google-appengine-java
 Issue Tracker - http://code.google.com/p/googleappengine/issues
Google Confidential and Proprietary 26
Monday, April 25, 2011 26