Add Java formatting tasks and CI check

.github/workflows/build.yml

@@ -9,6 +9,20 @@ permissions:
   contents: read
 
 jobs:
+  format:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up JDK 17
+        uses: actions/setup-java@v4
+        with:
+          distribution: zulu
+          java-version: '17'
+      - name: Set up Gradle
+        uses: gradle/actions/setup-gradle@v4
+      - name: Check Java formatting
+        run: ./gradlew formatCheck
+
   build:
     runs-on: ubuntu-latest
     steps:

README.md

@@ -38,6 +38,14 @@ Run `./gradlew publishToMavenLocal` to publish all three artifacts to your local
 Maven repository, using the version from the `artifacts/` configuration files.
 The published class files target Java 7, matching earlier SoLoader releases.
 
+## Formatting Java sources
+
+From this directory, run `./gradlew format` to format all Java sources, or
+`./gradlew formatCheck` to check them without making changes. Both commands work
+in a standalone checkout or in `fbsource/fbandroid/libraries/soloader` and use a
+pinned Google Java Format version downloaded by Gradle. No formatter binary is
+stored in the repository.
+
 The existing [Buck](https://buckbuild.com/) build is also available. Once you have
 Buck installed, run the following commands from the project root directory:
 ```shell

build.gradle

@@ -1,5 +1,25 @@
 plugins {
     id 'com.android.library' version '9.2.1' apply false
+    id 'com.diffplug.spotless' version '8.0.0'
+}
+
+spotless {
+    java {
+        target 'java/**/*.java'
+        googleJavaFormat('1.25.2')
+    }
+}
+
+tasks.register('format') {
+    group = 'formatting'
+    description = 'Format all SoLoader Java sources.'
+    dependsOn 'spotlessApply'
+}
+
+tasks.register('formatCheck') {
+    group = 'verification'
+    description = 'Check formatting of all SoLoader Java sources.'
+    dependsOn 'spotlessCheck'
 }
 
 def artifactVersions = ['ANNOTATION', 'NATIVELOADER', 'SOLOADER'].collect { artifact ->