chore: add spotless code style check

.github/PULL_REQUEST_TEMPLATE.md

@@ -11,8 +11,9 @@ XXXXX
 
 Follow this checklist to help us incorporate your contribution quickly and easily:
 
-- [ ] Read the [Contributing Guide](https://github.com/apolloconfig/apollo/blob/master/CONTRIBUTING.md) before making this pull request.
+- [ ] Read the [Contributing Guide](https://github.com/apolloconfig/apollo-java/blob/main/CONTRIBUTING.md) before making this pull request.
 - [ ] Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
+- [ ] Format your code with `mvn -B spotless:apply -Dmaven.gitcommitid.skip=true`  and `mvn -B -f apollo-compat-tests/pom.xml spotless:apply -Dmaven.gitcommitid.skip=true`
 - [ ] Write necessary unit tests to verify the code.
 - [ ] Run `mvn clean test` to make sure this pull request doesn't break anything.
 - [ ] Update the [`CHANGES` log](https://github.com/apolloconfig/apollo-java/blob/master/CHANGES.md).

.github/workflows/build.yml

@@ -46,6 +46,30 @@ jobs:
     - name: Compile
       run: mvn -B clean compile -Dmaven.gitcommitid.skip=true
 
+  code-style-check:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up JDK 8
+      uses: actions/setup-java@v4
+      with:
+        distribution: temurin
+        java-version: 8
+    - name: Cache Maven packages
+      uses: actions/cache@v4
+      with:
+        path: ~/.m2/repository
+        key: ${{ runner.os }}-maven-spotless-${{ hashFiles('**/pom.xml') }}
+        restore-keys: |
+          ${{ runner.os }}-maven-spotless-
+          ${{ runner.os }}-maven-
+    - name: Code Style Check
+      run: mvn -B spotless:check -Dmaven.gitcommitid.skip=true
+    - name: Code Style Check (compat-tests reactor)
+      run: mvn -B -f apollo-compat-tests/pom.xml spotless:check -Dmaven.gitcommitid.skip=true
+
   unit-integration-pr:
     runs-on: ubuntu-latest
     steps:

.gitignore

@@ -26,4 +26,4 @@ target
 # git
 *.orig
 .flattened-pom.xml
-
+config-cache/

.mergify.yml

@@ -31,6 +31,7 @@ queue_rules:
       - "check-success = compile-matrix (8)"
       - "check-success = compile-matrix (11)"
       - "check-success = compile-matrix (17)"
+      - "check-success = code-style-check"
       - "check-success = unit-integration-pr"
       - "check-success = compat-api"
       - "check-success = compat-spring-spring-3.1.1-jdk8"
@@ -56,6 +57,7 @@ queue_rules:
       - "check-success = compile-matrix (8)"
       - "check-success = compile-matrix (11)"
       - "check-success = compile-matrix (17)"
+      - "check-success = code-style-check"
       - "check-success = unit-integration-pr"
       - "check-success = compat-api"
       - "check-success = compat-spring-spring-3.1.1-jdk8"

CONTRIBUTING.md

@@ -0,0 +1,49 @@
+# Contributing to Apollo Java
+
+Thanks for contributing to [apolloconfig/apollo-java](https://github.com/apolloconfig/apollo-java)! This
+guide covers the project-specific steps needed before opening a pull request. The default branch of this
+repository is `main`.
+
+For general guidance on writing a good pull request description, see the
+[Apollo server contributing guide](https://github.com/apolloconfig/apollo/blob/master/CONTRIBUTING.md) — note
+that it documents the `apollo` (server) repository, so its build/format commands do not apply here.
+
+## Building and testing
+
+```bash
+mvn clean test
+```
+
+## Code style (Spotless)
+
+This repository is split across **two independent Maven reactors**:
+
+- the root [`pom.xml`](pom.xml), which aggregates the regular client modules
+  (`apollo-core`, `apollo-client`, `apollo-client-config-data`, `apollo-mockserver`, `apollo-openapi`,
+  `apollo-plugin`);
+- [`apollo-compat-tests/pom.xml`](apollo-compat-tests/pom.xml), which separately aggregates the
+  compatibility-test modules (`apollo-api-compat-it`, `apollo-spring-compat-it`,
+  `apollo-spring-boot-compat-it`).
+
+The root POM's `<modules>` list does **not** include `apollo-compat-tests`, so running Spotless from the
+repository root never touches the compatibility-test modules, and vice versa. CI checks both reactors as
+separate steps, so you must format and check **both** before pushing — running only the root command will
+pass locally and still fail CI.
+
+Format your code:
+
+```bash
+mvn -B spotless:apply -Dmaven.gitcommitid.skip=true
+mvn -B -f apollo-compat-tests/pom.xml spotless:apply -Dmaven.gitcommitid.skip=true
+```
+
+Verify formatting (this is what CI runs):
+
+```bash
+mvn -B spotless:check -Dmaven.gitcommitid.skip=true
+mvn -B -f apollo-compat-tests/pom.xml spotless:check -Dmaven.gitcommitid.skip=true
+```
+
+## Updating the changelog
+
+Update the [`CHANGES` log](CHANGES.md) to describe your change.