Clean up, bug fix and maven setup?

Author: hotpad100c

.github/workflows/maven.yml

@@ -13,10 +13,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v4
         with:
-          java-version: 17
+          java-version: 21
           distribution: temurin
 
       - name: Grant execute permission for gradlew