Convert an Object instance to the real subclass instance dynamically

Question

Background:

I have hundreds of XXXFaultMsg classes generated from a WSDL file, they all have a method getFaultMsg() but they are extended from Exception directly. I have a function with argument Exception e, where e might be instance of one of the XXXFaultMsg classes.

Challenge:

I want to invoke getFaultMsg() on e if it is an instance of XXXFaultMsg.

I have written if (e.getClass().getName().endsWith("FaultMsg")) to detect whether e is an instance of XXXFaultMsg. Then how can I declare a var with type XXXFaultMsg and cast e to it and call getFaultMsg() on it?

P.S. I don't want to construct a long list of if (e instanceof XXXFaultMsg) cause there are over 100 XXXFaultMsg classes.

but they are extended from Exception directly time to refactor maybe — Scary Wombat
– Scary Wombat, Commented Jan 27, 2017 at 0:32
If you're not able to restructure the classes, you would have to use reflection to call the method. — shmosel
– shmosel, Commented Jan 27, 2017 at 0:36
They are WebService client stubs generated from WSDL by JAX-WS and the WSDL file is provided other people. — Lee
– Lee, Commented Jan 27, 2017 at 0:43

takethefake · Accepted Answer · 2017-01-27 00:40:10Z

3

Say you have one method which takes no args:

Method methodToFind = null;
if (e.getClass().getName().endsWith("FaultMsg")){
    try {
      methodToFind = e.getClass().getMethod("getFaultMsg", (Class<?>[]) null);
    } catch (NoSuchMethodException | SecurityException e) {
      // Your exception handling goes here
    }
}

Invoke it if present:

if(methodToFind == null) {
   // Method not found.
} else {
   // Method found. You can invoke the method like
   methodToFind.invoke(e, (Object[]) null);
}

answered Jan 27, 2017 at 0:40

takethefake

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