Support Java 21 main launch protocol in prod and dev mode

Relates to: quarkusio#36154

core/deployment/src/main/java/io/quarkus/runner/bootstrap/StartupActionImpl.java

@@ -26,6 +26,7 @@
 import io.quarkus.bootstrap.app.RunningQuarkusApplication;
 import io.quarkus.bootstrap.app.StartupAction;
 import io.quarkus.bootstrap.classloading.QuarkusClassLoader;
+import io.quarkus.bootstrap.runner.MainMethodInvoker;
 import io.quarkus.builder.BuildResult;
 import io.quarkus.deployment.builditem.ApplicationClassNameBuildItem;
 import io.quarkus.deployment.builditem.DevServicesLauncherConfigResultBuildItem;
@@ -104,13 +105,12 @@ public RunningQuarkusApplication runMainClass(String... args) throws Exception {
         try {
             // force init here
             Class<?> appClass = Class.forName(className, true, runtimeClassLoader);
-            Method start = appClass.getMethod("main", String[].class);
             Thread t = new Thread(new Runnable() {
                 @Override
                 public void run() {
                     Thread.currentThread().setContextClassLoader(runtimeClassLoader);
                     try {
-                        start.invoke(null, (Object) (args == null ? new String[0] : args));
+                        MainMethodInvoker.invoke(appClass, args);
                     } catch (Throwable e) {
                         log.error("Error running Quarkus", e);
                         //this can happen if we did not make it to application init

independent-projects/bootstrap/runner/src/main/java/io/quarkus/bootstrap/runner/MainMethodInvoker.java

@@ -0,0 +1,73 @@
+package io.quarkus.bootstrap.runner;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+
+public final class MainMethodInvoker {
+
+    // follow the rules outlines in https://openjdk.org/jeps/445 section 'Selecting a main method'
+    public static void invoke(Class<?> mainClass, Object args)
+            throws InvocationTargetException, IllegalAccessException, NoSuchMethodException, InstantiationException {
+
+        // public static void main(String[] args)
+        Method mainWithArgs = null;
+        try {
+            mainWithArgs = mainClass.getDeclaredMethod("main", String[].class);
+            int modifiers = mainWithArgs.getModifiers();
+            if (Modifier.isStatic(modifiers) && !Modifier.isPrivate(modifiers)) {
+                if (!Modifier.isPublic(modifiers)) {
+                    mainWithArgs.setAccessible(true);
+                }
+                mainWithArgs.invoke(null, args);
+                return;
+            }
+        } catch (NoSuchMethodException ignored) {
+
+        }
+
+        // public static void main()
+        Method mainWithoutArgs = null;
+        try {
+            mainWithoutArgs = mainClass.getDeclaredMethod("main");
+            int modifiers = mainWithoutArgs.getModifiers();
+            if (Modifier.isStatic(modifiers) && !Modifier.isPrivate(modifiers)) {
+                if (!Modifier.isPublic(modifiers)) {
+                    mainWithoutArgs.setAccessible(true);
+                }
+                mainWithoutArgs.invoke(null);
+                return;
+            }
+        } catch (NoSuchMethodException ignored) {
+
+        }
+
+        var instance = mainClass.getConstructor().newInstance();
+
+        // public void main(String[] args)
+        if (mainWithArgs != null) {
+            int modifiers = mainWithArgs.getModifiers();
+            if (!Modifier.isPrivate(modifiers)) {
+                if (!Modifier.isPublic(modifiers)) {
+                    mainWithArgs.setAccessible(true);
+                }
+                mainWithArgs.invoke(instance, args);
+                return;
+            }
+        }
+
+        // public void main()
+        if (mainWithoutArgs != null) {
+            int modifiers = mainWithoutArgs.getModifiers();
+            if (!Modifier.isPrivate(modifiers)) {
+                if (!Modifier.isPublic(modifiers)) {
+                    mainWithoutArgs.setAccessible(true);
+                }
+                mainWithoutArgs.invoke(instance);
+                return;
+            }
+        }
+
+        throw new NoSuchMethodException("Unable to find main method");
+    }
+}

independent-projects/bootstrap/runner/src/main/java/io/quarkus/bootstrap/runner/QuarkusEntryPoint.java

@@ -1,5 +1,7 @@
 package io.quarkus.bootstrap.runner;
 
+import static io.quarkus.bootstrap.runner.MainMethodInvoker.invoke;
+
 import java.io.BufferedInputStream;
 import java.io.File;
 import java.io.IOException;
@@ -36,7 +38,7 @@ public static void main(String... args) throws Throwable {
         }
     }
 
-    private static void doRun(Object args) throws IOException, ClassNotFoundException, IllegalAccessException,
+    private static void doRun(String[] args) throws IOException, ClassNotFoundException, IllegalAccessException,
             InvocationTargetException, NoSuchMethodException {
         String path = QuarkusEntryPoint.class.getProtectionDomain().getCodeSource().getLocation().getPath();
         String decodedPath = URLDecoder.decode(path, "UTF-8");
@@ -57,8 +59,12 @@ private static void doRun(Object args) throws IOException, ClassNotFoundExceptio
             try {
                 Thread.currentThread().setContextClassLoader(appRunnerClassLoader);
                 QuarkusForkJoinWorkerThread.setQuarkusAppClassloader(appRunnerClassLoader);
+
                 Class<?> mainClass = appRunnerClassLoader.loadClass(app.getMainClass());
-                mainClass.getMethod("main", String[].class).invoke(null, args);
+
+                invoke(mainClass, args);
+            } catch (InstantiationException e) {
+                throw new RuntimeException(e);
             } finally {
                 QuarkusForkJoinWorkerThread.setQuarkusAppClassloader(null);
                 appRunnerClassLoader.close();