Add build.yml to workflows.

.github/workflows/build.yml

@@ -0,0 +1,32 @@
+name: build
+on: [pull_request, push]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        # Use these Java versions
+        java: [21]
+        # and run on both Linux and Windows
+        os: [ubuntu-20.04, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: checkout repository
+        uses: actions/checkout@v2
+      - name: validate gradle wrapper
+        uses: gradle/wrapper-validation-action@v1
+      - name: setup jdk ${{ matrix.java }}
+        uses: actions/setup-java@v1
+        with:
+          java-version: ${{ matrix.java }}
+      - name: make gradle wrapper executable
+        if: ${{ runner.os != 'Windows' }}
+        run: chmod +x ./gradlew
+      - name: build
+        run: ./gradlew build
+      - name: capture build artifacts
+        if: ${{ runner.os == 'Linux' && matrix.java == '21' }} # Only upload artifacts built from latest java on one OS
+        uses: actions/upload-artifact@v2
+        with:
+          name: Artifacts
+          path: build/libs/