Add Spotless plugin with removeUnusedImports check enabled

Closes #43233

Signed-off-by: stianst <stianst@gmail.com>

.github/workflows/ci.yml

@@ -90,6 +90,9 @@ jobs:
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
+      - name: Spotless
+        run: ./mvnw spotless:check
+
       - name: Build Keycloak
         uses: ./.github/actions/build-keycloak
 

CONTRIBUTING.md

@@ -110,6 +110,33 @@ git commit --signoff --message "This is the commit message"
 
 This option adds a `Signed-off-by` trailer at the end of the commit log message.
 
+### Spotless
+
+Spotless is used to check and apply code formatting. To check your code locally before sending a PR run:
+
+```
+./mvnw spotless:check
+```
+
+You can either use your IDE to fix these issues; or Spotless can fix them for you by running:
+
+```
+./mvnw spotless:apply
+```
+
+A good practice is to create a commit with your changes prior to running `spotless:apply` then you can see and
+review what changes Spotless has applied, for example by using a diff tool. Finally, if you are happy with the changes
+Spotless has applied you can amend the changes to your commit by running:
+
+```
+git add -a
+git commit --amend
+```
+
+Note: If you get the error `Could not find goal 'verify' in plugin com.diffplug.spotless:spotless-maven-plugin` you are
+probably running `mvn spotless:check` instead of `./mvnw spotless:check`. This is most likely a bug in Maven or the 
+Spotless plugin.
+ 
 ### Commit messages and issue linking
 
 The format for a commit message should look like:

boms/pom.xml

@@ -47,6 +47,7 @@
     <properties>
         <central.publishing.plugin.version>0.7.0</central.publishing.plugin.version>
         <nexus3.staging.plugin.version>1.0.7</nexus3.staging.plugin.version>
+        <spotless-plugin.version>3.0.0</spotless-plugin.version>
     </properties>
 
     <distributionManagement>
@@ -77,6 +78,11 @@
                         <nexusUrl>${jboss.repo.nexusUrl}</nexusUrl>
                     </configuration>
                 </plugin>
+                <plugin>
+                    <groupId>com.diffplug.spotless</groupId>
+                    <artifactId>spotless-maven-plugin</artifactId>
+                    <version>${spotless-plugin.version}</version>
+                </plugin>
             </plugins>
         </pluginManagement>
     </build>

pom.xml

@@ -207,6 +207,7 @@
         <smallrye.openapi.generator.plugin.version>3.6.2</smallrye.openapi.generator.plugin.version>
         <openapi.generator.plugin.version>6.3.0</openapi.generator.plugin.version>
         <build-helper-maven-plugin.version>3.2.0</build-helper-maven-plugin.version>
+        <spotless-plugin.version>3.0.0</spotless-plugin.version>
 
         <!-- Surefire Settings -->
         <surefire.memory.Xms>512m</surefire.memory.Xms>
@@ -1518,8 +1519,19 @@
                         <skip>${skipProtoLock}</skip>
                     </configuration>
                 </plugin>
+                <plugin>
+                    <groupId>com.diffplug.spotless</groupId>
+                    <artifactId>spotless-maven-plugin</artifactId>
+                    <version>${spotless-plugin.version}</version>
+                    <configuration>
+                        <java>
+                            <removeUnusedImports />
+                        </java>
+                    </configuration>
+                </plugin>
             </plugins>
         </pluginManagement>
+
     </build>
 
     <profiles>