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Major migrations�made easy

Tim te Beek

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Tim te Beek

Java Consultant

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Major migrations�over the past decade

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2009

��XML → Annotations

Component scanning

SOAP

Applets

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2.5

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2011

try ( Resource closeable = new Resource() ) { … }

List<String> diamonds = new ArrayList<>()

java.nio.file.Path

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2014

(Integer x, Integer y) -> { return x + y; }

LocalDate releaseDate = LocalDate.of(2014, 3, 18);

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2014 - Spring Boot 1.0

Jar not war

Opinionated

Non functionals

No XML

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2015

Decomposition

Communication & failures

NoSQL

Kubernetes 1.0

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2017

@BeforeEach, …

@Rule → Extension

@RunWith → @ExtendWith

assertThrows(Exception.class, () -> validate(invalidArgument))

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2018

List.of()

var

HttpClient

java.xml.ws ❌

java.xml.bind ❌

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2018 - Spring Boot 2.0

Java 7 ❌ Java 8+ ✅

Configuration Property Binding

WebFlux

Micrometer.io

Spring Data, Security, Cloud, Messaging, …

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2019

GitHub buys Dependabot

WhiteSource buys Renovate

Increased awareness

❌ = 👩‍💻

✅ = 🤔

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2021

Text blocks

record Point ( int x, int y ) { }

if ( object instanceof Integer i ) { }

return switch ( … ) { … };

--add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED

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2022

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2022 - Spring Boot 3.0

Java 17 baseline

Jakarta EE 9

Kotlin 1.6

Groovy 4.0

Gradle 7.3

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Change is the

only constant

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OpenRewrite

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Origin

Internal logging framework → SLF4J

Perfect transformation required

Abstract Syntax Tree parser & manipulation

Produce minimal changes

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Broader application

Onboarding stalled

Struggle with outdated libraries & frameworks

Spring Boot 1.x → 2.x

JUnit 4 → JUnit 5

Apache license 2.0

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Early focus on JVM

Search & transformation

Refactoring ecosystem

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AssertJ

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Abstract Syntax Tree

Type attribution

Format preservation

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OpenRewrite is not the only parser capable of understanding and manipulating Java.

There are others, such as JavaParser, which can achieve some of the same functionality.

However, two features set OpenRewrite apart from the competition.

The first is their focus on exact type attribution.

By having the exact type available on any tree element, they can be sure to only manipulate exact matches.

The second characteristic that sets OpenRewrite apart is their format preservation.

Their parser not only takes into account the functional code, but also the surrounding code style and indentation.

This allows them to accurately reproduce your source file, regardless of further changes.

Any changes made through OpenRewrite, look just like a colleague worked on your code.

Together, these features make OpenRewrite exceptionally good at safe code transformations.

Their changes are minimally invasive, and guaranteed to work, in part due to their do no harm mentality.

By manipulating the full Abstract Syntax Tree, OpenRewrite can far exceed simple search and replace operations.

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Recipes

Search & Refactor

Composition

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Visitors

Match & modify elements

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Modules

Search & Refactor

Composition

Specific purpose

Complete migrations

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JUnit 5 recipe

type: specs.openrewrite.org/v1beta/recipe

name: org.openrewrite.java.testing.junit5.JUnit4to5Migration

recipeList:

- org.openrewrite.java.ChangeType:

oldFullyQualifiedTypeName: org.junit.Test

newFullyQualifiedTypeName: org.junit.jupiter.api.Test

- org.openrewrite.java.testing.junit5.UpdateBeforeAfterAnnotations

- org.openrewrite.java.testing.junit5.AssertToAssertions

- org.openrewrite.java.testing.junit5.StaticImports

- org.openrewrite.java.testing.junit5.ExpectedExceptionToAssertThrows

- …

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JUnit 5 recipe

type: specs.openrewrite.org/v1beta/recipe

name: org.openrewrite.java.testing.junit5.JUnit4to5Migration

recipeList:

- org.openrewrite.java.ChangeType:

oldFullyQualifiedTypeName: org.junit.Test

newFullyQualifiedTypeName: org.junit.jupiter.api.Test

- org.openrewrite.java.testing.junit5.UpdateBeforeAfterAnnotations

- org.openrewrite.java.testing.junit5.AssertToAssertions

- org.openrewrite.java.testing.junit5.StaticImports

- org.openrewrite.java.testing.junit5.ExpectedExceptionToAssertThrows

- …

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Large migrations in small reusable steps

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Running recipes

./mvnw org.openrewrite.maven:rewrite-maven-plugin:4.24.0:run� -Drewrite.recipeArtifactCoordinates=� org.openrewrite.recipe:rewrite-spring:4.21.0� -DactiveRecipes=� org.openrewrite.java.spring.boot2.SpringBoot1To2Migration

Apply OpenRewrite plugin
With Module dependency
Run migration recipe

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PetClinic Migration

Spring Boot 1.5.x → 2.x

Java 8 → Java 17

JUnit 4 → JUnit 5

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Demo

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Applications

OpenRewrite

Migrate

Fix

Enforce

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Now that we have seen how OpenRewrite works,

Let’s have a look at what you can do with it.

Obviously by now we have seen that it is well suited to migrations.

You have mostly seen migrations from one version to another.

But you can also migrate from one framework to another.

If you want to switch from Log4J to SLF4J, you can.

Same thing for switching between JUnit and AssertJ.

And even larger migrations are in development.

Another application is fixing static analysis findings.

A large collection of CheckStyle, Sonar and Security findings are supported,

to allow you to reduce your technical debt in minutes.

Finally there is a whole class of recipes to enforce code style.

Rather than merely apply a formatter, these style recipes go a step further to actually change your code.

This ensures your code style reads consistently from project to project.

And in addition to what is already available, it’s fairly easy to add custom recipes specific to your projects.

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Future

OpenRewrite

Kotlin

Java 17

Typescript

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So, now that we have seen how it works, and what it can do, let’s briefly look ahead at what is still to come.

As you have seen, OpenRewrite has dedicated parsers for multiple languages already.

But, as you can imagine, they have some catching up to do still.

They are working on a parser for both Java 17 and Kotlin.

Note that you are perfectly able to run on Java 17, but you can not yet migrate to any of the new language features.

The interesting thing about Kotlin is going to be that Java migration recipes will just work, even though the languages look very different.

There have also been experiments to support TypeScript.�And although promising, it has not yet been made available.

All three of these features are in active development.

It is not yet clear when you can use any of this, but interesting developments nonetheless.

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Spring Boot Migrator

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“Spring Boot Migrator (SBM) aims to help developers�upgrade or migrate to Spring Boot by providing recipes for automated migrations.”

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Origin

VMWare Labs project, Q4 2020
Switched from JavaParser to OpenRewrite
Jan 2021 Fabian Krüger full-time lead
March 2022 open-sourced under Spring-projects-experimental
Opinionated API for migrations to Spring Boot
Compatible with OpenRewrite recipes

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Strong Spring focus

Java EE → Spring Boot

MuleSoft → Spring Integration

Upgrade Spring Boot

Adopt Spring Cloud

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Inform & guide

With HTML report

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Apply & iterate

Through interactive CLI

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Future

Spring Boot Migrator

Spring Framework 6 & Boot 3

Introduce new Spring Module

Generate context related code

Contextual guidance

Performance
Cloud readiness
Native readiness

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Moderne

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Apply at scale

Committed to Open Source Recipes

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app.moderne.io

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Contribute to Open Source

Find project in need of ❤️

Reduce technical debt 👷

Keep review effort comparable 🔍

Report missing recipes 🐛

Finish Spring PetClinic migration 🐶

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We could all use�more automation

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Closing

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Migrate safely,�quickly & in full

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Where to learn more

docs.openrewrite.org

github.com/openrewrite

github.com/spring-projects-experimental/spring-boot-migrator

app.moderne.io

RewriteOSS.slack.com

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Questions

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Thank you!

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