Make Java Smoke Test PR workflow generic

* so that it can be used for every Java samples

.github/workflows/test-pull-request-java.yml

@@ -1,63 +1,55 @@
-name: Test Pull Request (Java)
+name: Smoke Test Pull Request (Java)
 
 on:
   merge_group:
   pull_request:
     branches:
-    - main
+      - main
     paths:
-    - 'java/**'
-    - '!java/native-image/**'
-    - '!java/java-node/**'
+      - 'java/**'
 
 jobs:
-  smoke:
-    name: Smoke Tests
+  prepare:
+    name: Prepare
     runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.paths.outputs.matrix }}
     steps:
-    - name: Setup Go
-      uses: actions/setup-go@v4
-      with:
-        go-version: 1.18.x
-
-    - name: Checkout
-      uses: actions/checkout@v4
-
-    - name: Cache local Gradle repository
-      uses: actions/cache@v3
-      with:
-        path: |
-          ~/.gradle/caches
-          ~/.gradle/wrapper
-        key: ${{ runner.os }}-gradle-${{ hashFiles('java/**/*.gradle*', 'java/**/gradle-wrapper.properties') }}
-        restore-keys: |
-          ${{ runner.os }}-gradle-
-
-    - name: Cache local Maven repository
-      uses: actions/cache@v3
-      with:
-        path: |
-          ~/.m2/repository
-          ~/.m2/wrapper
-        key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml', 'java/**/maven-wrapper.properties') }}
-        restore-keys: |
-          ${{ runner.os }}-maven-
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Discover changed paths
+        id: paths
+        run: |
+          env
+          # see: https://stackoverflow.com/a/8721550/24069 for usage of paste
+          changed_java_folders=$( git diff --name-only --merge-base origin/$GITHUB_BASE_REF $GITHUB_SHA  | xargs -n 1 dirname | uniq | grep -v "^\." | sed "s/^/\"/;s/$/\"/" | paste -s -d, - )
+          echo "These are the Java folders where we found changes for this PR : $changed_java_folders" >> $GITHUB_STEP_SUMMARY
+          echo "matrix={\"java_sample_folder\":[$changed_java_folders]}" >> $GITHUB_OUTPUT
+          echo "This is how the matrix will look like: $(cat $GITHUB_OUTPUT)"
 
-    - name: Setup Directories
-      run: |
-        #!/usr/bin/env bash
-        set -euo pipefail
-
-        mkdir -p ~/.m2/repository
-        mkdir -p ~/.m2/repository/wrapper/dists
-        mkdir -p ~/.gradle/caches
-        mkdir -p ~/.gradle/wrapper/dists
-        chmod -R 775 ~/.m2
-        chmod -R 775 ~/.gradle
+  smoke:
+    needs: prepare
+    name: Smoke Tests
+    runs-on: ubuntu-latest
+    strategy:
+      matrix: ${{ fromJSON(needs.prepare.outputs.matrix) }}
+    #        java_sample_folder:
 
-    - name: Test Java Samples
-      run: |
-        ./scripts/smoke.sh --suite java \
-                           --builder paketobuildpacks/builder:full \
-                           --builder paketobuildpacks/builder:base \
-                           --builder paketobuildpacks/builder:tiny
+    steps:
+      - name: Setup Go
+        uses: actions/setup-go@v4
+        with:
+          go-version: 1.18.x
+
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Smoke Test Java samples
+        run: |
+          echo "About to run the smoke test script against this suite folder: ${{ matrix.java_sample_folder }}/smoke_test"
+          ./scripts/smoke.sh --suite ${{ matrix.java_sample_folder }}/smoke_test \
+                             --builder paketobuildpacks/builder:full \
+                             --builder paketobuildpacks/builder:base \
+                             --builder paketobuildpacks/builder:tiny