This presentation was held at the Spring One 2GX 2015 conference in Washington DC. The presentation explains how to migrate an existing Grails 2 application to the new Spring Boot and Gradle based Grails 3. It covers migrating plugins, applications and features gotchas as well as best praciteces. The conference presentation also included an extensive live coding section in which I migrated an existing application to Grails 3.

1. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
SPRINGONE2GX
WASHINGTON, DC
Migrating from Grails 2 to Grails 3
Michael Ploed - innoQ
@bitboss

2. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Grails 3 is the most major and
radical change in the history of Grails
2
+ =

3. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
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HOW
TO
MIGRATE
3

4. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
HOW
TO
MIGRATE
4
A Grails
application usually
consists of the
application and
various plugins

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HOW
TO
MIGRATE
5
An application
usually integrates
with many
standard and
some self written
plugins

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Don’t add
complexity. Wait
until your major
external plugins
have been migrated
6

7. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
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Grails 3 has different file / directory locations
7
Grails 2 Grails 3
grails-app/conf/BuildConfig.groovy build.gradle
grails-app/conf/Config.groovy grails-app/conf/application.groovy
grails-app/conf/UrlMappings.groovy grails-app/controllers/UrlMappings.groovy
grails-app/conf/BootStrap.groovy grails-app/init/BootStrap.groovy
scripts src/main/scripts
src/groovy src/main/groovy
src/java src/main/groovy
test/unit src/test/groovy
test/integration src/integration-test/groovy
web-app src/main/webapp or src/main/resources/
*GrailsPlugin.groovy src/main/groovy

8. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
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Files that are not present in Grails 2.x
8
New File Explanation
build.gradle Gradle build script
gradle.properties Gradle build properties
grails-app/conf/logback.groovy
Logging has been extracted from Config.groovy and
is now being defined via Logback
grails-app/conf/application.yml
You can now also configure your application with
YAML
grails-app/init/PACKAGE_PATH/Application.groovy The Application class that is used by Spring Boot to
start the Grails 3 application

9. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Unneeded files after a successful migration
9
Obsolete File Explanation
application.properties
Moved to build.gradle (for application name and
version)
grails-app/conf/DataSource.groovy Merged to application.yml
lib
Dependency resolution should be used to resolve
JAR files
web-app/WEB-INF/applicationContext.xml
Removed, beans should now be defined in grails-app/
conf/spring/resources.groovy
src/templates/war/web.xml
No longer needed for Grails 3. Do customization via
Spring
web-app/WEB-INF/sitemesh.xml Removed, sitemesh filter is no longer present
web-app/WEB-INF/tld
Removed, can be restored in src/main/webapp or src/
main/resources/WEB-INF

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Before and after
interceptors have been
removed
They need to be
replaced by standalone
interceptors

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General migration steps 1/2
11
Grails 2
Grails 3
create-app
create-plugin
src/java
src/groovy
src/main/groovy
grails-app
grails-app
test/unit
test/integration
test-unit
src/integration-
test/groovy

12. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
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General migration steps 2/2
12
Grails 2
Grails 3
Fix Build
(imports)
Config.groovy to application.groovy
BuildConfig
build.groovy Merge DataSource.groovy
Move log4j config to Logback
C
L
E
A
N
U
P

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Step 1
Migrate Plugins

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Mind the Plugin directory
on the Grails Website.
It focusses on Grails 1.x -
2.x plugins
Grails 3 Plugins are on
Bintray

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Steps to take for plugin migration
There are several steps you have to take for migrating a plugin
• Create a new Grails 3 plugin
• Copy Sources
• Handle the plugin descriptor
• Add dependencies to the build
• Modify package imports
• Migrate configuration
• Register ArtefactHandler definitions
• Migrate code generation scripts
• Delete unnecessary files
15

16. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
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Handle Plugin Descriptor
You must copy the Plugin descriptor from the Grails2 application to
src/main/groovy/grails/plugins/[pluginname]
After that you have to add the correct package declaration to the plugin descriptor
16
package grails.plugins.recaptcha
class RecaptchaGrailsPlugin {
…
}

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Register Artefact Handler Definitions
If you have ArtefactHandler definitions written in Java you have to declare them in
src/main/resources/META-INF/grails.factories
This step can be ignored for Groovy based ArtefactHandlers, Grails detects them.
17
grails.core.ArtefactHandler=grails.plugins.quartz.JobArtefactHandler

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Migrate code generation scripts
Old Gant code generation scripts have to be replaced by Code Generation Scripts
or Gradle tasks.
Simple code generation can easily be migrated to the new code generation API
More complex tasks are better of with a migration to Gradle tasks
18

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Simple code generation example
19
includeTargets << grailsScript("_GrailsCreateArtifacts")
target(createJob: "Creates a new Quartz scheduled job") {
depends(checkVersion, parseArguments)
def type = "Job"
promptForName(type: type)
for (name in argsMap.params) {
name = purgeRedundantArtifactSuffix(name, type)
createArtifact(name: name, suffix: type, type: type, path: "grails-app/jobs")
createUnitTest(name: name, suffix: type)
}
}
setDefaultTarget 'createJob'

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Gradle Tasks for complex generation scripts
20
import …
class RunQueryCommand implements ApplicationCommand {
@Autowired
DataSource dataSource
boolean handle(ExecutionContext ctx) {
def sql = new Sql(dataSource)
println sql.executeQuery("select * from foo")
return true
}
}
> grails create-command run-query

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Command can be added to classpath in build.gradle
21
buildscript {
…
dependencies {
classpath "org.grails.plugins:myplugin:0.1-SNAPSHOT"
}
}
…
dependencies {
runtime "org.grails.plugins:myplugin:0.1-SNAPSHOT"
}
> grails run-query

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Step 2
Migrate Application

23. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
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Steps to take for application migration
There are several steps you have to take for migrating a application
• Create a new Grails 3 application
• Copy Sources
• Add dependencies to the build
• Migrate Configuration
• Migrate web.xml Modifications to Spring
• Migrate static assets not handled by Asset pipeline
• Migrate Tests
• Delete unnecessary files
23

24. Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a
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Step 3
Test intensively

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Let’s migrate an application
25

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Recap - Migration Steps
26
Plugins App Test

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SPRINGONE2GX
WASHINGTON, DC
Thank You!
Michael Ploed - innoQ
Twitter: @bitboss
Slides: http://slideshare.net/mploed