Upgrade to Micronaut Framework 4 with OpenRewrite and Gradle

The Micronaut team has assembled a new set of OpenRewrite recipes to make upgrading from Micronaut Framework 3 to Micronaut Framework 4 quick and straightforward.

These recipes automate as much as possible from our previous “Upgrade To Micronaut Framework 4” post. The recipes will be continually updated whenever we discover new upgrade steps.

Upgrading a Gradle Application to Micronaut Framework 4

If you use Gradle to build your Micronaut applications, it is easy to update from Micronaut Framework 3 to Micronaut Framework 4 with the OpenRewrite Gradle plugin. You need to apply the recipes from the rewrite-micronaut module. There are two approaches:

• Modify your build.gradle directly with the necessary configuration.
• Create an external Gradle init script that can be applied to any project.

If you’ve not used OpenRewrite before, follow the steps to modify your build.gradle directly in an application you’d like to try to upgrade, as it will help you get more familiar with the pieces involved. Once you are comfortable with how the OpenRewrite Gradle plugin works in your environment, then you can move towards creating a general init script to use on multiple applications.

Modifying build.gradle directly

Some minor additions can be made to your build.gradle file to enable the necessary OpenRewrite Gradle tasks for the upgrade. The necessary steps are:

1. Enable the OpenRewrite Gradle plugin
2. Add the rewrite-micronaut dependency
3. Activate the Micronaut 3-to-4 upgrade recipe
4. Execute the newly configured Gradle tasks

Enabling the OpenRewrite Gradle plugin

The OpenRewrite Gradle plugin org.openrewrite.rewrite must be added to the plugins section of a Micronaut 3 app build.gradle as below:

plugins {     id("org.openrewrite.rewrite") version("latest.release") }

Adding the rewrite-micronautdependency

Next add the rewrite module org.openrewrite.recipe:rewrite-micronaut to your dependencies section in build.gradle:

dependencies {     rewrite("org.openrewrite.recipe:rewrite-micronaut:2.1.1") }

Activating the Micronaut Framework 3-to-4 upgrade recipe

Finally you must make the Micronaut Framework 4 migration recipe active by adding the following to build.gradle

rewrite {     activeRecipe("org.openrewrite.java.micronaut.Micronaut3to4Migration") }

Executing the OpenRewrite Gradle tasks

The OpenRewrite Gradle plugin provides a set of tasks for listing and executing recipes against a configured application.

To execute the configured Micronaut Framework 4 migration recipe and see what actions it will take without making any actual changes to your source code, you can execute:

./gradlew rewriteDryRun

If the dry run executes without any errors and you are satisfied with the changes that the OpenRewrite recipe makes, you can then apply the changes to your application source code by executing:

./gradlew rewriteRun

And that’s it, you now should have a fully functional Micronaut 4 application!

Using a Gradle init script

Once you are comfortable with how OpenRewrite works, see the alternate approach outlined in the OpenRewrite documentation of using a Gradle init script to externalize your OpenRewrite configuration.

In taking this approach, you will first want to revert the OpenRewrite configuration changes (if any) that you’ve made directly to your application’s build.gradle file.

We have built a sample init script that you can use as a starting point.

Feedback, Issue Reports, and Pull Requests welcome!

If you encounter any issues in applying the recipe to your own application, please raise an issue here, and contributions via pull request are always welcome.