Ensure that ConversionService.canConvert(Enum) no longer throws an exception

[moonfruit]

In my project, I use the following code to find an appropriate method to execute for a given class. It throws an IllegalArgumentException: The target type java.lang.Enum does not refer to an enum when there is a more appropriate “method”: asString(CharSequence).

public class MyTest {

    public static void main(String[] args) throws AccessException {
        EvaluationContext evaluationContext = SimpleEvaluationContext.forReadOnlyDataBinding().build();
        ReflectiveMethodResolver methodResolver = new ReflectiveMethodResolver();
        MethodExecutor asString = methodResolver.resolve(evaluationContext, MyTest.class, "asString",
                Collections.singletonList(TypeDescriptor.valueOf(String.class)));
        TypedValue result = asString.execute(evaluationContext, MyTest.class, "value");
        System.out.println(result);
    }

    public static String asString(Enum<?> left) {
        return left.name();
    }

    public static String asString(CharSequence left) {
        return left.toString();
    }
}

After doing some research I realized that the root cause was that StringToEnumConverterFactory.getConverter(Enum.class) threw an exception when it couldn't convert and resolve the concrete Enum. This directly causes ConversionService.canConvert(String.class,Enum.class) to throw an exception. I don't think the method canConvert() should throw an exception, it returns true if it can convert and false if it can't. That's what this method is for, to avoid throwing an exception when calling the convert method directly.

So I've modified StringToEnumConverterFactory and IntegerToEnumConverterFactory a little and hopefully this PR will be accepted.

[moonfruit]

Hi, @sbrannen. Is there something else I should change?