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migrate-2-grails3

A Grails 2 plugin that performs a partial migration of a Grails 2 plugin or application to Grails 3

Prerequisites

Grails 2.x and 3.x are installed where 2.x is the Grails version of the project being migrated, and 3.x is the target Grails version

Usage

  • Set the current Grails version to 3.x
  • Create an empty Grails 3.x project with the same name and type (application or plugin) as the Grails 2.x project being migrated
  • Install this plugin in the Grails 2.x project being migrated, i.e. add the following to BuildConfig.groovy replacing ${version} with the latest version of this plugin
plugins {
    build ':migrate2-grails3:${version}'
    // other plugin dependencies
}
  • Set the current Grails version to 2.x
  • Compile the Grails 2.x project
  • Execute the following command in the Grails 2.x project

grails migrate [path-to-grails3-project]

  • Once this command has completed, the plugin can be removed from the Grails 2.x app

Arguments

  • path-to-grails3-project the relative path from the Grails 2.x project to the Grails 3.x project

Example

If the Grails 2.x being migrated is located at /home/grails2/foo and the Grails 3.x project is at /home/grails3/foo execute the following on the command-line with the current Grails version set to 2.x and the current directory set to /home/grails2/foo

grails migrate ../../grails3/foo

On Windows, it may be necessary to use backslashes instead

grails migrate ..\..\grails3\foo

Tasks Performed Automatically

The plugin performs the tasks listed in the "Project Structure Changes" section of the migration guide. After following the instructions above, if the project being migrated is a plugin, steps 1-3 of the Upgrading Plugins section will also have been performed. if the project being migrated is an application, steps 1-2 of the Upgrading Applications section will have been performed.

A few of other minor tasks are attempted which aren't explicitly mentioned in the migration guide, e.g. copying of README.md and LICENSE files from the root of the Grails 2.x project to the root of the Grails 3.x project.

Mandatory Exceptions

Some of the steps described in the aforementioned sections of the migration guide are not performed by this plugin and must be performed manually instead:

  • merging DataSource.groovy and Config.groovy into a single application.yml or application.groovy config file with log4j config removed
  • configuring logging via logback.groovy
  • migrating dependencies from BuildConfig.groovy to build.gradle
  • setting the application/plugin version in build.gradle

Optional Exceptions

Some of the steps described in the aforementioned sections of the migration guide are not performed by this plugin and may need to be performed manually instead. In other words, dependending of the contents of the project being migrated, each of the following steps may not be relevant

  • migrating dependencies from lib directory to build.gradle
  • migrating Spring beans from web-app/WEB-INF/applicationContext.xml to grails-app/conf/spring/resources.groovy
  • Customizations to web.xml that were applied via src/templates/war/web.xml must be applied via Spring in Grails 3.x
  • migrating .tld files in web-app/WEB-INF/tld

Gant Scripts

Any Gant scripts in the scripts directory of the Grails 2.x project will be copied to the src/main/scripts directory of the Grails 3.x project. However the contents of these scripts must be migrated from Gant to Gradle, as described in step 7 of the plugin migration guide.

Improvements

There are a few additional migration steps that it may be possible to automate, but I need some feedback before I can implement them. Check the issue list and contribute feedback/code if possible.