build_and_deploy.yml

name: Build and Deploy
on: [push, pull_request]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v2.3.1

      - name: Build
        run: |
          ./gradlew run

# deploy to github pages only when on master
  deploy:
    runs-on: ubuntu-latest
    needs: build
    steps:
      - name: Extract branch name	
        shell: bash
        run: echo "##[set-output name=branch;]$(echo ${GITHUB_REF##*/})"
        id: extract_branch
      - name: Checkout
        uses: actions/checkout@v2.3.1
        if: ${{ github.event_name != 'pull_request' && steps.extract_branch.outputs.branch == 'master' }}
      - name: Build
        run: |
          ./gradlew run
        if: ${{ github.event_name != 'pull_request' && steps.extract_branch.outputs.branch == 'master' }}	  
      - name: Deploy
        uses: JamesIves/github-pages-deploy-action@4.1.4
        with:
          branch: gh-pages
          folder: output
        if: ${{ github.event_name != 'pull_request' && steps.extract_branch.outputs.branch == 'master' }}