Use reflection for test to fix compiling core to older Java versions

README.md

@@ -46,6 +46,7 @@ You can download them from here: https://ci.codemc.org/job/Games647/job/FastLogi
 
     fastlogin.bukkit.command.premium
     fastlogin.bukkit.command.cracked
+
     fastlogin.command.premium.other
     fastlogin.command.cracked.other
 

core/pom.xml

@@ -40,10 +40,8 @@
     <packaging>jar</packaging>
 
     <properties>
-        <maven.compiler.source>8</maven.compiler.source>
-        <maven.compiler.target>8</maven.compiler.target>
-        <!-- Make Java 21 test method available in this multi-release project: Caution of breaking older systems -->
-        <maven.compiler.release>21</maven.compiler.release>
+        <!-- Still force Java 8 for the remaining project -->
+        <maven.compiler.release>8</maven.compiler.release>
     </properties>
 
     <name>FastLoginCore</name>

core/src/test/java/com/github/games647/fastlogin/core/AsyncSchedulerTest.java

@@ -33,6 +33,7 @@ import org.junit.jupiter.api.condition.JRE;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.lang.reflect.InvocationTargetException;
 import java.util.concurrent.Executors;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -63,8 +64,14 @@ class AsyncSchedulerTest {
     }
 
     private static void setVirtual(AtomicBoolean virtual) {
-        if (Thread.currentThread().isVirtual()) {
-            virtual.set(true);
+        boolean isVirtual;
+        try {
+            isVirtual = (boolean) Thread.class.getDeclaredMethod("isVirtual").invoke(Thread.currentThread());
+            if (isVirtual) {
+                virtual.set(true);
+            }
+        } catch (IllegalAccessException | InvocationTargetException | NoSuchMethodException ex) {
+            ex.printStackTrace();
         }
     }
 }