Handling Java Optional in JXPath object hierachy?

Question

I have an object graph and one of the accessor methods returns a java Optional and as a result my XPath expression stops from that point onwards.

The xpath is data/someData[1]/optionalObject/field

How can I get JXPath to return the actual object rather than the Optional or does JXPath pre date java Optionals and so it will never work?

score 0 · Answer 1 · answered Feb 01 '19 at 12:23

If anyone is interested I solved the issue with Optional objects by creating a custom NodePointerFactory instance. I could not find any documentation on doing this, but I hope the below helps anyone who comes across this problem as well.

Steps are as follows.

Register the instance with the call

JXPathContextReferenceImpl.addNodePointerFactory(new OptionalHandlerPointerFactory());

The implementation

private static class OptionalHandlerPointerFactory implements NodePointerFactory {

@Override
public int getOrder() {
    //Insert before the bean pointer factory
    return BeanPointerFactory.BEAN_POINTER_FACTORY_ORDER - 1;
}

@Override
public NodePointer createNodePointer(QName name, Object bean, Locale locale) {
    if(bean != null && bean instanceof Optional) {
        if(!((Optional)bean).isPresent()) {
            return new NullPointer(name, locale);           
        }

        final Object beanObject = ((Optional)bean).get();
        final Class beanClass  = beanObject.getClass();

        JXPathBeanInfo bi = JXPathIntrospector.getBeanInfo(beanClass);
        return new BeanPointer(name, beanObject, bi, locale);               
    }

    return null;
}       

@Override
public NodePointer createNodePointer(NodePointer parent, QName name, Object bean) {
    if(bean != null && bean instanceof Optional ) {
        if(!((Optional)bean).isPresent()) {
            return new NullPointer(parent, name);                   
        }

        final Object beanObject = ((Optional)bean).get();
        final Class beanClass  = beanObject.getClass();

        final JXPathBeanInfo bi = JXPathIntrospector.getBeanInfo(beanClass);
        return new BeanPointer(parent, name, beanObject, bi);                   
    }

    return null;
}

}

Handling Java Optional in JXPath object hierachy?

1 Answers1