support google java style

Author: realDuYuanChao

.github/workflows/checkstyle.yml

@@ -0,0 +1,24 @@
+name: Code Formatter
+
+on: [push]
+
+jobs:
+  format:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - name: Set up JDK 12
+        uses: actions/setup-java@v1
+        with:
+          java-version: 12
+      - run: wget https://github.com/google/google-java-format/releases/download/google-java-format-1.9/google-java-format-1.9-all-deps.jar -O formatter.jar
+      - run: java -jar formatter.jar --replace --set-exit-if-changed $(find . -type f -name "*.java")
+      - name: Commit Format changes
+        if: failure()
+        run: |
+          git config --global user.name github-actions
+          git config --global user.email '${GITHUB_ACTOR}@users.noreply.github.com'
+          git remote set-url origin https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY
+          git commit -am "Formatted with Google Java Formatter"
+          git push --force origin HEAD:$GITHUB_REF