ci: publish docs site to datafusion.apache.org/java/ (#26)

.asf.yaml

diff --git a/.asf.yaml b/.asf.yaml
index 175f349..821ab5e 100644
--- a/.asf.yaml
+++ b/.asf.yaml
@@ -53,3 +53,9 @@
     allow_update_branch: true
     allow_auto_merge: true
     del_branch_on_merge: true
+
+# publishes the content of the `asf-site` branch to
+# https://datafusion.apache.org/java/
+publish:
+  whoami: asf-site
+  subdir: java

.github/workflows/docs.yaml

diff --git a/.github/workflows/docs.yaml b/.github/workflows/docs.yaml
new file mode 100644
index 0000000..2cd6162
--- /dev/null
+++ b/.github/workflows/docs.yaml
@@ -0,0 +1,95 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+name: Deploy DataFusion Java site
+
+on:
+  push:
+    branches:
+      - main
+    paths:
+      - .asf.yaml
+      - .github/workflows/docs.yaml
+      - docs/**
+  pull_request:
+    branches:
+      - main
+    paths:
+      - .asf.yaml
+      - .github/workflows/docs.yaml
+      - docs/**
+
+permissions:
+  contents: write
+
+jobs:
+  build-docs:
+    name: Build docs
+    if: ${{ startsWith(github.repository, 'apache/') }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout docs sources
+        uses: actions/checkout@v4
+
+      - name: Checkout asf-site branch
+        if: github.event_name == 'push'
+        uses: actions/checkout@v4
+        with:
+          ref: asf-site
+          path: asf-site
+
+      - name: Setup Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.10"
+
+      - name: Install dependencies
+        run: |
+          set -x
+          python3 -m venv venv
+          source venv/bin/activate
+          pip install --upgrade pip
+          pip install -r docs/requirements.txt
+
+      - name: Build docs
+        run: |
+          set -x
+          source venv/bin/activate
+          cd docs
+          ./build.sh
+
+      - name: Copy & push the generated HTML
+        if: github.event_name == 'push'
+        run: |
+          set -x
+          cd asf-site
+          rsync \
+            -a \
+            --delete \
+            --exclude '/.git/' \
+            ../docs/build/html/ \
+            ./
+          cp ../.asf.yaml .
+          touch .nojekyll
+          git status --porcelain
+          if [ -n "$(git status --porcelain)" ]; then
+            git config user.name "github-actions[bot]"
+            git config user.email "github-actions[bot]@users.noreply.github.com"
+            git add --all
+            git commit -m "Publish built docs triggered by ${{ github.sha }}"
+            git push || git push --force
+          fi