Grails 2 to 3 upgrade

gistfile1.txt

Intro
Application was converted from a Grails 2 to a Grails 3 app in July 2016.
This was no small undertaking, a number of differences are documented here (http://docs.grails.org/3.0.x/guide/upgrading.html) but this doc barely scratches the surface.
The reason for the change was, 1 to stay current, Grails 2 was no longer supported and 2 to take advantage of the new architecture, Grails 3 is built on Spring boot so we get Actuator out of the box, and Grails 3 uses the Gradle build system so we can take advantage of being able to use e.g. jacoco for analysis.

IDE
Intellij IDEA is the only fully featured IDE to support Grails 3 at present.
Once your version of Grails 3 has been downloaded, install IDEA then create a Grails application.
You then need to copy the existing sources from the version 2 app to version 3
 
cd D:\WS\GRAILS\3.1.8
grails create-app myAppG3
robocopy /e D:\WS\GRAILS\2.4.4\myApp\src\groovy D:\WS\GRAILS\3.1.8\myAppG3\src\main\groovy
robocopy /e D:\WS\GRAILS\2.4.4\myApp\src\java D:\WS\GRAILS\3.1.8\myAppG3\src\main\groovy
robocopy /e D:\WS\GRAILS\2.4.4\myApp\grails-app D:\WS\GRAILS\3.1.8\myAppG3\grails-app
robocopy /e D:\WS\GRAILS\2.4.4\myApp\test\unit D:\WS\GRAILS\3.1.8\myAppG3\src\test\groovy
robocopy /e D:\WS\GRAILS\2.4.4\myApp\test\integration D:\WS\GRAILS\3.1.8\myAppG3\src\integration-test\groovy
The following sections describe the changes made to various parts of the application

Changes

All
References to org.codehaus.* have been replaced, this differed depending on the import, lots of differences in test packages, a handful in main codebase

Spring security
There's largely no change here apart from some naming convention changes to some of the parameters which affect e.g. custom login pages.
myApp uses a custom login page named \views\login\auth.gsp
The name of the username and password parameters had to be changed from j_username to username and j_password to password

Controllers
Seem to HAVE to return something now from controller methods, whereas in 2.4.4 I could e.g. just set something in the flash if there were no database results,
in 3.1.8 the screen is totally blank.
Any random statement seems to work e.g. return, println 'hello' new ModelAndView(), [:]

MyService
Dependency to GroovyMBean was broken when code 1st imported, turns out the version of groovy pulled in by IDEA wasn't the *-all version so was missing JMX
related stuff, fixed issue by adding compile "org.codehaus.groovy:groovy-jmx:2.4.7" to build.gradle

AsyncService
Asynchronous plugin not available for Grails 3, replaced the following:
runAsync {
try {
    params.taskId = task.id
    log.warn "Started task ${task.id} for service $serviceName method $serviceMethod params $params"
    Holders.getApplicationContext().getBean( serviceName )."${serviceMethod}"( params )
}
catch ( any ) {
    taskService.addMessage( task.id, any.message, MessageType.ERROR )
}
finally {
    log.warn "Task ${task.id} completed"
    taskService.endTask( task.id )
}
}
with:
Promise p = task {
    params.taskId = shTask.id
    log.warn "Started task ${shTask.id} for service $serviceName method $serviceMethod params $params"
    Holders.getApplicationContext().getBean( serviceName )."${serviceMethod}"( params )
}
p.onError { Throwable err ->
    err.printStackTrace()
    taskService.addMessage( shTask.id, err.message, MessageType.ERROR )
}
p.onComplete {
    log.warn "Task ${shTask.id} completed"
    taskService.endTask( shTask.id )
}
Now making use of grails.async.* code.

Data binding in async code
Quite a few strange issues around data binding of Grails domain objects using map constructors in asynchronous code.
A number of the async tasks involve parsing a csv file then creating a domain object from it, this was done using the domain objects map constructor.
For some (still unknown) reason this would fail after a random number of object creations, generally the fields would all end up assigned null values and the domain validation would fail on the call to save( failOnError: true ).
Also tried making relevant classes implement the Trait grails.web.databinding.DataBinder then call method bindData( object, map ) but this didn't work either.
Had to change to direct setting of each value on the object which is clearly not as efficient from a coding POV, needs more investigation.

resources.groovy

2.4.4 version contained following
multipartResolver( org.springframework.web.multipart.commons.CommonsMultipartResolver ) {
    maxInMemorySize=1000000000
    maxUploadSize=10000000000
}
This prevented file uploads from working, the file object was not present in the request at all.
Turns out CommonsMultipartResolver has been replaced by another implementation and the following replaces functionality in application.yml
grails:
    upload:
        maxRequestSize: 1000000000
        maxFileSize: 1000000000

======================================================
There's another method of accessing the grails application object in resources.groovy:
"${grailsApplication.config.grails.plugin.springsecurity.ldap.search.base}"
although the previous method still works:
application.config.grails.plugin.springsecurity.ldap.search.base
application.groovy
static rules for spring security controller annotations syntax needed changing from:
grails.plugin.springsecurity.controllerAnnotations.staticRules = [
    '/': ['permitAll'],
    '/index': ['permitAll'],
]
To:
grails.plugin.springsecurity.controllerAnnotations.staticRules = [
    [pattern: '/myApp', access: ['permitAll']],
    [pattern: '/', access: ['permitAll']]
]

Twitter bootstrap
Changed method of pulling in bootstrap, in 2.4.4. a plugin was used, in 3.1.8 it's pulled in using webjars e.g. from build.gradle
compile "org.webjars:bootstrap:3.3.5"

Missing dependency
Grails code wouldn't compile due to missing dependency on org.apache.commons.fileupload.FileItemFactory, resolved by adding the following to build.gradle
compile "commons-fileupload:commons-fileupload:1.3.2"
This was odd as dependency appears in build.gradle for the project

Database update migration
To prevent Grails from trying to create/update... the database you no longer specify the dbCreate option at all, if it's there and empty Grails still tries to do something, just don't specify anything at all.
To allow Grails to see the database migration files add the following to build.gradle
sourceSets {
    main {
        resources {
            srcDir 'grails-app/migrations'
            }
        }
    }

External libraries
No lib directory is created in the root of the project anymore, created a directory named extLibs in root and added following to build.gradle:
dependencies {
...
compile fileTree( dir: 'extlibs', include: '*.jar' )
...
}

Integration tests
IntegrationSpec class no longer exists, now make integration tests extend Specification as per unit tests and add @Integration annotation to class from grails.test.mixin.integration package
Can no longer add to the database in setup method due to transaction not being available, see http://docs.grails.org/latest/guide/testing.html#integrationTesting, you'll get a No Hibernate Session found error if you try
database migration plugin
In 2.4.4 config you'd specify a list of filenames to use for startup under the key updateOnStartFileNames, this has changed to a single property named updateOnStartFileName
static resources
Resources e.g. javascript that are only required for individual areas are now accessed through the asset pipeline syntax {{<asset:javascript src="customer.js" />}}, the resource itself goes in grails-app/assets/javascripts

Information messages
Information messages are fetched from a mongoDB and placed at top of screen, this stopped working, no errors, had to change the following in InfoMessageController
render ( view: 'messages', model:[infoMessageList: msgs] )
To
render ( template: 'messages', model:[infoMessageList: msgs] )
And rename messages.gsp to _messages.gsp

Deploy
Eventually decided to upgrade to Tomcat 8 after various issues when building the war file.
Initially tried to deploy to Tomcat 7 as previous but the was was bundled with a bunch of embedded Tomcat 8 jars which caused a problem when starting Tomcat 7.
You can stop the jars from being bundled in the war's /WEB-INF/lib directory by changing the dependency in build.gradle from
compile "org.springframework.boot:spring-boot-starter-tomcat"
to
provided "org.springframework.boot:spring-boot-starter-tomcat"
All this does however is put the jars in /WEB-INF/lib-provided, then Tomcat 7 gets so far during startup and complains that it's missing a class that is in the core embedded tomcat jar.
So installed tomcat 8.