Question

have a following problem:

I have an abstract class with a method “call” that basically calls some otherMethod and if otherMethod throws an Exception I try to fix in catch by relogging and calling the “call” method again.

public Object call(String methodName, Object[] parameters, Class[] parameterTypes) throws RetryingException, RemoteException {
    while (true) {
        try {
            return callMethod(methodName, parameters, parameterTypes);
        } catch (SomeException e) {
            if (numberOfTriesLeft-- == 0) {
                throw new RetryingException();
            }
            login();
        }
    }
}

Now I have a subclass of this class with overriden method call that may take a null parameter. Basically if such situation happens I want to call the method from superclass, but the Exception mentioned above is not thrown, thus, no retry and method ends failing somewhere else. Is there a way to throw it manually and pass further or any other way to fix it? Thank you for your help!

@Override
public Object call(String methodName, Object[] parameters, Class[] parameterTypes) throws RetryingException, RemoteException {
    if (parameters[0] == null){
        // What to do here if I want to throw SomeException here to end up in a catch block from the call method in the superclass? Or how to change it
    }
    // Everything ok. No null params
    ...
    return super.call(methodName, parameters, parameterTypes);
}

Answer 1

From my experience, what you could do is to have a parent method like so:

public final Object call(String methodName, Object[] parameters, Class[] parameterTypes) throws RetryingException, RemoteException {
    try {
        callMethod(methodName, parameters, parameterTypes)
    } catch (Exception ex) {
        // Handle any exception here...
    }
}

protected Object callMethod(String methodName, Object[] parameters, Class[] parameterTypes) throws RetryingException, RemoteException {
    // .. your code
}

And then override the callMethod (child) method instead:

@Override
protected Object callMethod(String methodName, Object[] parameters, Class[] parameterTypes) throws RetryingException, RemoteException {
    // Exception thrown here will now be caught!
    return super.callMethod(methodName, parameters, parameterTypes);
}

So this has separated the interface methods from the overrideable methods. I see this pattern quite a lot in existing APIs.

Some points:

• call is now final stopping it from being overridden.
• callMethod is protected making it only override-able and callable from the same package – taking it out of the public API.

Update: Taken on board the point provided by @Fildor.