Add a page to upgrade to Spring Boot 4

Author: timtebeek

site/docs/upgrade-your-projects/upgrade-spring-boot-4.md

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+---
+sidebar_position: 7
+---
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+# Upgrade to Spring Boot 4.0
+
+To upgrade your project from Spring Boot 3.x to Spring Boot 4.0, you can [use the OpenRewrite recipe](https://docs.openrewrite.org/recipes/java/spring/boot4/upgradespringboot_4_0-community-edition) `org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0` from `rewrite-spring`.
+
+This recipe will automatically update your Spring Boot dependencies to version 4.0 and apply the necessary code changes to ensure compatibility, including updating deprecated APIs, migrating configuration properties, and adapting to framework changes introduced in Spring Boot 4.0.
+
+You can run the migration recipe using one of the following methods.
+
+<Tabs groupId="projectType">
+<TabItem value="moderne-cli" label="Moderne CLI">
+
+The Moderne CLI allows you to run OpenRewrite recipes on your project without needing to modify your build files,
+against serialized Lossless Semantic Tree (LST) of your project for a considerable performance boost & across projects.
+
+You will need to have configured the [Moderne CLI](https://docs.moderne.io/user-documentation/moderne-cli/getting-started/cli-intro) on your machine before you can run the following command.
+
+1. If project serialized Lossless Semantic Tree is not yet available locally, then build the LST.
+   This is only needed the first time, or after extensive changes:
+```bash title="shell"
+mod build ~/workspace/
+```
+
+2. If the recipe is not available locally yet, then you can install it once using:
+```shell title="shell"
+mod config recipes jar install org.openrewrite.recipe:rewrite-spring:LATEST
+```
+
+3. Run the recipe.
+```shell title="shell"
+mod run ~/workspace/ --recipe org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0
+```
+
+</TabItem>
+<TabItem value="maven-command-line" label="Maven Command Line">
+
+You will need to have [Maven](https://maven.apache.org/download.cgi) installed on your machine before you can run the following command.
+
+```shell title="shell"
+mvn -U org.openrewrite.maven:rewrite-maven-plugin:run -Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-spring:RELEASE -Drewrite.activeRecipes=org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0 -Drewrite.exportDatatables=true
+```
+
+</TabItem>
+<TabItem value="maven" label="Maven POM">
+
+You may add the plugin to your `pom.xml` file, so that it is available for all developers and CI/CD pipelines.
+
+1. Add the following to your `pom.xml` file:
+
+```xml title="pom.xml"
+<project>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.openrewrite.maven</groupId>
+        <artifactId>rewrite-maven-plugin</artifactId>
+        <version>LATEST</version>
+        <configuration>
+          <exportDatatables>true</exportDatatables>
+          <activeRecipes>
+            <recipe>org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0</recipe>
+          </activeRecipes>
+        </configuration>
+        <dependencies>
+          <dependency>
+            <groupId>org.openrewrite.recipe</groupId>
+            <artifactId>rewrite-spring</artifactId>
+            <version>LATEST</version>
+          </dependency>
+        </dependencies>
+      </plugin>
+    </plugins>
+  </build>
+</project>
+```
+
+2. Run run the recipe.
+```shell title="shell"
+mvn rewrite:run
+```
+
+</TabItem>
+<TabItem value="gradle-init-script" label="Gradle init script">
+
+Gradle init scripts are a good way to try out a recipe without modifying your `build.gradle` file.
+
+1. Create a file named `init.gradle` in the root of your project.
+
+```groovy title="init.gradle"
+initscript {
+    repositories {
+        maven { url "https://plugins.gradle.org/m2" }
+    }
+    dependencies { classpath("org.openrewrite:plugin:latest.release") }
+}
+rootProject {
+    plugins.apply(org.openrewrite.gradle.RewritePlugin)
+    dependencies {
+        rewrite("org.openrewrite.recipe:rewrite-spring:latest.release")
+    }
+    rewrite {
+        activeRecipe("org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0")
+        setExportDatatables(true)
+    }
+    afterEvaluate {
+        if (repositories.isEmpty()) {
+            repositories {
+                mavenCentral()
+            }
+        }
+    }
+}
+```
+
+2. Run the recipe.
+
+```shell title="shell"
+gradle --init-script init.gradle rewriteRun
+```
+
+</TabItem>
+<TabItem value="gradle" label="Gradle">
+
+You can add the plugin to your `build.gradle` file, so that it is available for all developers and CI/CD pipelines.
+
+1. Add the following to your `build.gradle` file:
+
+```groovy title="build.gradle"
+plugins {
+    id("org.openrewrite.rewrite") version("latest.release")
+}
+
+rewrite {
+    activeRecipe("org.openrewrite.java.spring.boot4.UpgradeSpringBoot_4_0")
+    setExportDatatables(true)
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    rewrite("org.openrewrite.recipe:rewrite-spring:latest.release")
+}
+```
+
+2. Run `gradle rewriteRun` to run the recipe.
+
+</TabItem>
+</Tabs>