CODEWITHSUNDEEP
grailsgroovy
Sudhir N
Sudhir N

Reputation: 4096

Groovy - How to replace methods of existing java classes

How do I replace methods of an existing java class (GrailsDataBinder in my case). I read that method calls for java classes doesnt go through invokeMethod, and hence it doesn't work, but I think there would be some solution.

I just tried this

GrailsDataBinder.metaClass.static.createBinder = {Object target, String objectName ->   
  throw new RuntimeException() 
}

And this

GrailsDataBinder.class.metaClass.static.createBinder = {Object target, String 
  objectName -> throw new RuntimeException() 
}

But that did not seem to have replaced the method, as my closure isn't being invoked, but instead the original method executes.

update

I just found that the closure is being executed if I call the createBinder from the test class itself - so it works and method is replaced

void testDataBinder() {
    GrailsDataBinder.createBinder(null, null)
}

However When it is invoked from DataBindingUtils, it always executes original method (DataBindingUtils is also a java class)

Following is the code inside DataBindingUtils that invokes the method.

binder = GrailsDataBinder.createBinder(object, object.getClass().getName());

Note : There are some similar questions asked earlier, but none of them have worked for me.

Upvotes: 1

Views: 1631

Answers (1)

Todd W Crone
Todd W Crone

Reputation: 1195

This is disappointing once you see the power of Groovy. However, as you already know, many of the cool metaclass etc. features available in Groovy simply don't work as you would like on Java classes.

If you are trying to override, stub or mock stuff on a Java class for unit testing etc., I advise looking into Spock, because it uses 'magic' that actually works on Java classes also.

If you are try to override methods for some other reason, you should try extending the Java class with a Groovy class or 'wrapping' the Java class with a Groovy class to gain the metaclass features you want when external classes call you classes methods. Unfortunately this still won't allow you to intercept calls that the Java class makes to itself.

Upvotes: 2

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