quarkusio/quarkus · error · RuntimeException

Unable to find a valid main method on class '${originalMainC

Error message

Unable to find a valid main method on class '${originalMainClassName}'. See https://openjdk.org/jeps/445 for details of what constitutes a valid main method.

What it means

After locating the configured main class, Quarkus transforms its bytecode to generate a standard static main entry point. doApply validates that the class contains a valid main-method candidate per JEP 445 rules (public static void main(String[]), or supported instance forms); if none is valid, this RuntimeException is thrown pointing at the JEP 445 definition.

Source

Thrown at core/deployment/src/main/java/io/quarkus/deployment/steps/MainClassBuildStep.java:590

     */
    private static class MainMethodTransformer implements BiFunction<String, ClassVisitor, ClassVisitor> {

        private final IndexView index;

        public MainMethodTransformer(IndexView index) {
            this.index = index;
        }

        @Override
        public ClassVisitor apply(String mainClassName, ClassVisitor outputClassVisitor) {
            ClassInfo mainClassInfo = index.getClassByName(mainClassName);
            if (mainClassInfo == null) {
                throw new IllegalStateException(mainClassName + " should have a corresponding ClassInfo at this point");
            }
            ClassTransformer transformer = new ClassTransformer(mainClassName);
            Result result = doApply(mainClassName, outputClassVisitor, transformer, mainClassInfo);
            if (!result.isValid) {
                throw new RuntimeException(errorMessage(mainClassName));
            }
            if (result.classVisitor == null) {
                throw new IllegalStateException("result.classvisitor should not be null at this point");
            }
            return result.classVisitor;
        }

        private Result doApply(String originalMainClassName,
                ClassVisitor classVisitor, ClassTransformer transformer,
                ClassInfo currentClassInfo) {
            boolean isTopLevel = currentClassInfo.name().toString().equals(originalMainClassName);
            boolean allowStatic = isTopLevel;
            boolean hasStaticWithArgs = false;
            boolean hasStaticWithoutArgs = false;
            boolean hasInstanceWithArgs = false;
            boolean hasInstanceWithoutArgs = false;

            MethodInfo withArgs = currentClassInfo.method("main", STRING_ARRAY);

View on GitHub (pinned to e1c734241f)

Solutions

1. Declare the main method as public static void main(String[] args) in the configured class
2. Fix the signature casing/modifiers of the existing main method
3. Add the missing String[] parameter or remove unsupported extra parameters
4. Check the quarkus.main-class value points at the class that actually contains the main method

Example fix

// before
public class Main {
    void main() { System.out.println("hi"); }
}
// after
public class Main {
    public static void main(String[] args) { System.out.println("hi"); }
}

Class<?> c = Main.class;
for (Method m : c.getDeclaredMethods()) {
    if (m.getName().equals("main")
            && java.lang.reflect.Modifier.isPublic(m.getModifiers())
            && java.lang.reflect.Modifier.isStatic(m.getModifiers())
            && Arrays.equals(m.getParameterTypes(), new Class<?>[]{String[].class})) {
        return; // valid
    }
}
throw new IllegalStateException("No valid public static void main(String[]) on " + c.getName());

try {
    quarkusBuild();
} catch (RuntimeException e) {
    if (e.getMessage() != null && e.getMessage().contains("Unable to find a valid main method")) {
        // fix the main method signature per JEP 445
    }
    throw e;
}

When it happens

Trigger: In the ClassVisitor's apply(): Result.isValid is false after scanning the main class and its hierarchy — no method matching a valid main signature exists on the class configured as quarkus.main-class or auto-detected main class.

Common situations: Main method declared with the wrong signature (non-static, non-public, missing String[] parameter, wrong casing 'Main'); main method with an incompatible parameter type; class only has a 'void main()' instance method under a Java version whose support doesn't match; abstract class without an inherited concrete main.

Related errors

• Failed to open path tree with root %s
• Dev services for ${request.getName()} requires a startable s
• Name cannot start with '/':${name}
• The class (${name}) cannot be created during deployment.
• Use GeneratedServiceProviderBuildItem to register service pr

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/03336ba5a8459cc3. Report an issue: GitHub.