"Unable to find unambiguous method" when overriding a generic method that has more than one parameter ----------------------------------------------------------------------------------------------------- Key: WFLY-7763 URL: https://issues.jboss.org/browse/WFLY-7763 Project: WildFly Issue Type: Bug Components: JSF Affects Versions: 10.1.0.Final Reporter: Tobias Liefke Assignee: Farah Juma I've written a generic typed class, which is extended by a class which binds the type variable: {code:java} public abstract class AppendableController<A extends Appendable> { public String append(A appendable, Number number) { // ... } } @Named public class WriterController extends AppendableController<Writer> { @Override public String append(Writer writer, Number number) { //.... } public Writer getWriter() { return new StringWriter(); } public Writer getNoWriter() { return null; } } {code} If I reference the {{append}} method in an JSF expression, I found many cases where this will result in an _MethodNotFoundException_ with the message: {code}Unable to find unambiguous method{code} Examples: * Case 1: {{writerController.append(writerController.writer, 1)}} -> _Unable to find unambiguous method: WriterController.append(java.io.StringWriter, java.lang.Long)_ * Case 2: {{writerController.append(writerController.noWriter, 1)}} -> _Unable to find unambiguous method: class org.example.WriterController.append(null, java.lang.Long)_ The reason is that {{WriterController.class.getMethods()}} returns both methods {{AppendableController.append(Appendable, Number)}} and {{WriterController.append(Writer, Number)}}. I see two problems here: * The type of the parameter is not derived from the type of the parameter expression. This will lead to non-deterministic behavior of the expression. Either because there are optional parameters, which might be null (see case 2), or parameters are sometimes proxied resp. extensions of the parameter type (see case 1). * In truth there is nothing unambiguous in this example, because both methods map to the same method invocation of the overridden method, no matter which I would call. It would be safe to call either of them.