(Quick Reference) # 3.3 Upgrading from Grails 2.x Version: 3.2.8 ## Table of Contents ## 3.3 Upgrading from Grails 2.x This guide takes you through the fundamentals of upgrading a Grails 2.x application or plugins to Grails 3.x. ## 3.3.1 Upgrading Plugins To upgrade a Grails 2.x plugin to Grails 3.x you need to make a number of different changes. This documentation will outline the steps that were taken to upgrade the Quartz plugin to Grails 3, each individual plugin may differ. #### Step 1 - Create a new Grails 3 plugin The first step is to create a new Grails 3 plugin using the command line:
    $ grails create-plugin quartz
This will create a Grails 3 plugin in the `quartz` directory. #### Step 2 - Copy sources from the original Grails 2 plugin The next step is to copy the sources from the original Grails 2 plugin to the Grails 3 plugin:
    # first the sources
    cp -rf ../quartz-2.x/src/groovy/ src/main/groovy
    cp -rf ../quartz-2.x/src/java/ src/main/groovy
    cp -rf ../quartz-2.x/grails-app/ grails-app
    cp -rf ../quartz-2.x/QuartzGrailsPlugin.groovy src/main/groovy/grails/plugins/quartz

    # then the tests
    cp -rf ../quartz-2.x/test/unit/* src/test/groovy
    mkdir -p src/integration-test/groovy
    cp -rf ../quartz-2.x/test/integration/* src/integration-test/groovy

    # then templates / other resources
    cp -rf ../quartz-2.x/src/templates/ src/main/templates
#### Step 3 - Alter the plugin descriptor You will need to add a package declaration to the plugin descriptor. In this case `QuartzGrailsPlugin` is modified as follows:
    // add package declaration
    package grails.plugins.quartz
    ...
    class QuartzGrailsPlugin extends Plugin {
     ...
    }
In addition you should remove the `version` property from the descriptor as this is now defined in `build.gradle`. #### Step 4 - Update the Gradle build with required dependencies The repositories and dependencies defined in `grails-app/conf/BuildConfig.groovy` of the original Grails 2.x plugin will need to be defined in `build.gradle` of the new Grails 3.x plugin:
    compile("org.quartz-scheduler:quartz:2.2.1") {
        exclude group: 'slf4j-api', module: 'c3p0'
      }
It is recommended to use the latest stable, Grails 3+ compatible version of plugins. (Grails 2.x plugin versions will not work.) #### Step 5 - Modify Package Imports In Grails 3.x all internal APIs can be found in the `org.grails` package and public facing APIs in the `grails` package. The `org.codehaus.groovy.grails` package no longer exists. All package declaration in sources should be modified for the new location of the respective classes. Example `org.codehaus.groovy.grails.commons.GrailsApplication` is now `grails.core.GrailsApplication`. #### Step 5 - Migrate Plugin Specific Config to application.yml Some plugins define a default configuration file. For example the Quartz plugin defines a file called `grails-app/conf/DefaultQuartzConfig.groovy`. In Grails 3.x this default configuration can be migrated to `grails-app/conf/application.yml` and it will automatically be loaded by Grails without requiring manual configuration merging. #### Step 6 - Update plugin exclusions Old plugins may have a `pluginExcludes` property defined that lists the patterns for any files that should not be included in the plugin package. This is normally used to exclude artifacts such as domain classes that are used in the plugin’s integration tests. You generally don’t want these polluting the target application. This property is no longer sufficient in Grails 3, and nor can you use source paths. Instead, you must specify patterns that match the paths of the compiled classes. For example, imagine you have some test domain classes in the `grails-app/domain/plugin/tests` directory. You should first change the `pluginExcludes` value to
    def pluginExcludes = ["plugin/test/**"]
and then add this block to the build file:
    jar {
        exclude "plugin/test/**"
    }
The easiest way to ensure these patterns work effectively is to put all your non-packaged class into a distinct Java package so that there is a clean separation between the main plugin classes and the rest. #### Step 7 - Register ArtefactHandler Definitions In Grails 3.x ArtefactHandler definitions written in Java need to be declared in a file called `src/main/resources/META-INF/grails.factories` since these need to be known at compile time.
| If the `ArtefactHandler` is written in Groovy this step can be skipped as Grails will automatically create the `grails.factories` file during compilation.
The Quartz plugin requires the following definition to register the `ArtrefactHandler`:
    grails.core.ArtefactHandler=grails.plugins.quartz.JobArtefactHandler
#### Step 8 - Migrate Code Generation Scripts Many plugins previously defined command line scripts in Gant. In Grails 3.x command line scripts have been replaced by two new features: Code generation scripts and Gradle tasks. If your script is doing simple code generation then for many cases a code generation script can replace an old Gant script. The `create-job` script provided by the Quartz plugin in Grails 2.x was defined in `scripts/CreateJob.groovy` as:
    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'
A replacement Grails 3.x compatible script can be created using the `create-script` command:
    $ grails create-script create-job
Which creates a new script called `src/main/scripts/create-job.groovy`. Using the new code generation API it is simple to implement:
    description("Creates a new Quartz scheduled job") {
        usage "grails create-job <<JOB NAME>>"
        argument name:'Job Name', description:"The name of the job"
    }

    model = model( args[0] )
    render  template:"Job.groovy",
            destination: file( "grails-app/jobs/$model.packagePath/${model.simpleName}Job.groovy"),
            model: model
Please refer to the documentation on Creating Custom Scripts for more information. #### Migrating More Complex Scripts Using Gradle Tasks Using the old Grails 2.x build system it was relatively common to spin up Grails inside the command line. In Grails 3.x it is not possible to load a Grails application within a code generation script created by the create-script command. Instead a new mechanism specific to plugins exists via the create-command command. The `create-command` command will create a new ApplicationCommand, for example the following command will execute a query:
    import grails.dev.commands.*
    import javax.sql.*
    import groovy.sql.*
    import org.springframework.beans.factory.annotation.*

    class RunQueryCommand implements ApplicationCommand {

      @Autowired
      DataSource dataSource

      boolean handle(ExecutionContext ctx) {
          def sql = new Sql(dataSource)
          println sql.executeQuery("select * from foo")
          return true
      }
    }
With this command in place once the plugin is installed into your local Maven cache you can add the plugin to both the build classpath and the runtime classpath of the application’s `build.gradle` file:
    buildscript {
      ...
      dependencies {
        classpath "org.grails.plugins:myplugin:0.1-SNAPSHOT"
      }
    }
    ...
    dependencies {
      runtime "org.grails.plugins:myplugin:0.1-SNAPSHOT"
    }
Grails will automatically create a Gradle task called `runQuery` and a command named `run-query` so both the following examples will execute the command:
    $ grails run-query
    $ gradle runQuery
#### Step 8 - Delete Files that were migrated or no longer used You should now delete and cleanup the project of any files no longer required by Grails 3.x (`BuildConfig.groovy`, `Config.groovy`, `DataSource.groovy` etc.) ## 3.3.2 Upgrading Applications Upgrading applications to Grails 3.x will require that you upgrade all plugins the application uses first, hence you should follow the steps in the previous section to first upgrade your plugins. #### Step 1 - Create a New Application Once the plugins are Grails 3.x compatible you can upgrade the application. To upgrade an application it is again best to create a new Grails 3 application using the "web" profile:
    $ grails create-app myapp
    $ cd myapp
#### Step 2 - Migrate Sources The next step is to copy the sources from the original Grails 2 application to the Grails 3 application:
    # first the sources
    cp -rf ../old_app/src/groovy/ src/main/groovy
    cp -rf ../old_app/src/java/ src/main/groovy
    cp -rf ../old_app/grails-app/ grails-app

    # then the tests
    cp -rf ../old_app/test/unit/ src/test/groovy
    mkdir -p src/integration-test/groovy
    cp -rf ../old_app/test/integration/ src/integration-test/groovy
#### Step 3 - Update the Gradle build with required dependencies The repositories and dependencies defined in `grails-app/conf/BuildConfig.groovy` of the original Grails 2.x application will need to be defined in `build.gradle` of the new Grails 3.x application. #### Step 4 - Modify Package Imports In Grails 3.x all internal APIs can be found in the `org.grails` package and public facing APIs in the `grails` package. The `org.codehaus.groovy.grails` package no longer exists. All package declaration in sources should be modified for the new location of the respective classes. Example `org.codehaus.groovy.grails.commons.GrailsApplication` is now `grails.core.GrailsApplication`. #### Step 5 - Migrate Configuration The configuration of the application will need to be migrated, this can normally be done by simply renaming `grails-app/conf/Config.groovy` to `grails-app/conf/application.groovy` and merging the content of `grails-app/conf/DataSource.groovy` into `grails-app/conf/application.groovy`. Note however that Log4j has been replaced by `grails-app/conf/logback.groovy` for logging, so any logging configuration in `grails-app/conf/Config.groovy` should be migrated to logback format. #### Step 6 - Migrate web.xml Modifications to Spring If you have a modified `web.xml` template then you will need to migrate this to Spring as Grails 3.x does not use a web.xml (although it is still possible to have on in `src/main/webapp/WEB-INF/web.xml`). New servlets and filters can be registered as Spring beans or with ServletRegistrationBean and FilterRegistrationBean respectively. #### Step 7 - Migrate Static Assets not handled by Asset Pipeline If you have static assets in your `web-app` directory of your Grails 2.x application such as HTML files, TLDs etc. these need to be moved. For public assets such as static HTML pages and so on these should go in `src/main/resources/public`. TLD descriptors and non public assets should go in `src/main/resources/WEB-INF`. As noted earlier, `src/main/webapp` folder can also be used for this purpose but it is not recommended. #### Step 8 - Migrate Tests Once the package names are corrected unit tests will continue to run, however any tests that extend the deprecated and removed JUnit 3 hierarchy will need to be migrated to Spock or JUnit 4. Integration tests will need to be annotated with the Integration annotation and should not extend GroovyTestCase or any JUnit 3 super class. ## 3.3.3 General Changes to be aware of when migrating apps There are other miscellaneous changes between Grails 2.x and Grails 3.x that it may help to be aware of when migrating your applications and plugins. Minor changes may be required. #### Domain classes The Constraints section of a Domain Class (or other validateable object) looks like this:
    static constraints = {
      name nullable: true, blank: false
      myField nullable: true
      another unique: true
    }
In Grails 2.x, fields with no constraints could be declared in the Constraints block, as a method call with no arguments. Example (NB. the following syntax is no longer supported):
    static constraints = {
      name nullable: true, blank: false
      mySimpleProperty()                  // <- A field that has no constraints. This syntax is not supported in Grails 3.
      anotherProperty unique: true
    }
A different syntax has to be used in Grails 3. Either remove the field declaration from the constraints block (if there are no constraints to specify for it), or to keep the field placeholder, pass an empty map argument: `\[:\]` instead of `()`. Replacement code for Grails 3.x:
    static constraints = {
      name nullable: true, blank: false
      mySimpleProperty [:]                // <- Empty map argument instead of ()
      anotherProperty unique: true
    }
If such declarations have not yet been changed then a log message like this emits on startup:
    ORM Mapping Invalid: Specified config option <<mySimpleProperty>> does not exist for class [example.MyDomainClass]
#### Multi-project builds (Grails 2.x inline plugins) If your project had inline plugins in Grails 2.x, contains ASTs, or if your project is composed of several modules or related applications then you may decide to restructure your project as a Gradle multi-project build. Sample multi-project structure:
    + example
        + example-app   <-- Main app
        + example-core  <-- Shared code plugin
        + example-ast   <-- AST transformations plugin
How to configure this is documented in the Plugins section under the heading 'Inline Plugins in Grails 3.0'. #### Migrating from Grails 2.x to Grails 3.1+ During the progress of migrating code from Grails 2.4 to Grails 3.1+, your project (and the plugins that your project depends on) will be moving to GORM 5 (or higher) and other newer library versions. You might also wish to familiarise yourself with the differences mentioned in the section Upgrading from Grails 3.0. #### AST Transformations If your application contains AST transformations, please be aware that for these to be applied to your application code, they must now be contained within a plugin. (In Grails 2.x it was possible to pre-compile AST transformations then apply them to your application code by hooking into compile events in `_Events.groovy`. This is no longer possible. Move your AST Transformation classes and associated annotations into a plugin for this purpose.) There are two AST patterns on which you can base migration of your AST transformer code: Groovy way: Use Groovy AST transformation annotations. Grails way: Use Grails AST transformer annotations. ##### Groovy AST transformations Import `org.codehaus.groovy.transform.GroovyASTTransformation` Annotate your transformation class with `GroovyASTTransformation(phase=CompilePhase.CANONICALIZATION)` A useful example app can be found here: grails3ast ##### Grails AST transformations Import `grails.compiler.ast.AstTransformer` Annotate your transformation class with `AstTransformer` Implement applicable interfaces, particularly if you are transforming Artefacts, e.g. `implements GrailsArtefactClassInjector, AnnotatedClassInjector` Your Transformer class must reside in a package under org.grails.compiler, otherwise it will not be detected. Example: org.grails.compiler.myapp Examples can be found in the Grails source code Example reference: ControllerActionTransformer.java #### Deployment to containers Grails uses Spring Boot to embed a Tomcat or Jetty instance by default. To build a war file for deployment to a container you will need to make a simple change to `build.gradle` (so that a container is not embedded). If you deploy to a Tomcat 7 container then there is an additional step. Grails 3 is built against Tomcat 8 APIs by default. You will need to change the target Tomcat version in the build to 7. There are standalone deployment options available. Refer to the Deployment guide for further details. #### Multiple datasources If your application uses multiple datasources, then be aware that the way these are declared in `application.yml` or `application.groovy` (previously `DataSources.groovy`) has changed. If there is more than one DataSource in an application there is now a `dataSources { …​ }` configuration block to contain them all. Previously, multiple `dataSource` declarations were used, with an underscore and suffix on the additional datasources, e.g. `dataSource_lookup { …​ }`. Please refer to the user guide section on Multiple Datasources for examples. #### Improvements to dependency injection In your Grails 2.x app you may have used Spring `@Autowired` in a few situations, such as dependency injection into certain base classes, and for typed field dependency injection. For example:
    @Autowired
    org.quartz.Scheduler quartzScheduler
Grails now has support for dependency injection into typed fields in addition to untyped `def` fields, following the usual Grails conventions of field name matching the bean property name. Example:
    GrailsApplication grailsApplication
You may find that `@Autowired` no longer works as it did previously in your code on artefacts or base classes, in certain scenarios, resulting in NULL for these fields. Changing these to a simple typed Grails dependency following the Grails naming convention and removing `@Autowired` should resolve this. | Quick Reference (hide)