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I'm trying to inspect Groovy generated methods on some CGLib proxied Groovy class, from Java, to learn what the return and parameter types are for methods. Ex, consider this Groovy class:

class Person {
  String name
}

Groovy generates getName() and setName() methods for the name property. getName() presumably returns a String and setName() presumably takes a String.

But when proxying this class via CGLib and intercepting invocations against the getName using CGLib's MethodInterceptor, method.getName() returns getMetaClass and method.getReturnType() returns groovy.lang.MetaClass.

Is there a way to learn the actual method name and return type from inside a MethodInterceptor?

Edit: Here's the call stack when intercepting an invocation of Person.getName():

ExplicitMappingInterceptor.intercept(Object, Method, Object[], MethodProxy) line: 42    
GroovyMMTester$A$$EnhancerByCGLIB$$915b5b4.getMetaClass() line: not available   
CallSiteArray.createPogoSite(CallSite, Object, Object[]) line: 144  
CallSiteArray.createCallSite(CallSite, Object, Object[]) line: 161  
CallSiteArray.defaultCall(CallSite, Object, Object[]) line: 45  
AbstractCallSite.call(Object, Object[]) line: 108   
AbstractCallSite.call(Object) line: 112 
GroovyMMTester$Map.configure() line: 18 <-- Person.getName() call is in here, but doesn't show
Jonathan
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  • Whats the reason to use CGLib and not [Metaclass](http://groovy.codehaus.org/Evaluating+the+MetaClass+runtime)? – ChrLipp Aug 23 '13 at 07:13
  • I guess that what you are calling is getName() on a Person object and not directly Person.getName(). Right? – Alfergon Aug 24 '13 at 10:02

2 Answers2

1

I think the problem you have is basically that you have the Java thinking of calling a method will call the method directly and be done with it. Well not even Java does that, but those things are hidden in the JVM. Groovy has not the luxury of modifying the JVM, so a set of methods might be called before the final method is called. Since this is an implementation detail the sequence may vary. And since Groovy is a language with runtime meta programming the target method you expect might not be called at all.

Anyway, to be able to call the method getName() in Groovy, the Groovy runtime first has to get the meta class of the Object the call is made on, which results in a call to getMetaClass(). If you intercept here, then you might never get to that method call you want.

The solution is actually easy... you just filter those helper methods. That would be any method starting with $ and any method starting with this$, as well as super$, and the getMetaClass method. Filtering means here you do not intercept, but simply continue the call by using Reflection. If you met one method that is not in that set, then you most probably have the target. in your example method.getName() will then return "getName".

blackdrag
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0

Please check/share the code you use for calling the getName() method as sometimes when asking for a property to a groovy object it uses the getProperty or getAttribute methods, and both of them call the getStaticMetaClass() method, which I think is what is actually happening to you.

What I mean is that instead of calling directly getName o a Person object it's actually callling the method getProperty(..., personObject, 'name', ...) which calls getStaticMetaClass().getProperty(..., personObject, 'name', ...).

You can also try to debug your code putting a breakpoint on the line you call method.getName() for example and look on the stacktrace how is the getName() method being called.

Alfergon
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  • OP wants to know the return type using reflection in Java. :) – dmahapatro Aug 18 '13 at 01:10
  • I'm using CGLib to proxy the class, and CGLib's [MethodInterceptor](http://cglib.sourceforge.net/apidocs/net/sf/cglib/proxy/MethodInterceptor.html) to intercept invocations against getName/setName. This is my starting point from which I wish to learn the "property type". Unfortunately, there doesn't seem to be a way from the interceptor to even learn what the name of the method was since `method.getName()` returns `$getStaticMetaClass`. – Jonathan Aug 20 '13 at 18:25
  • Without dumping a bunch of code, I basically just create the proxy using CGLib's Enhancer class and passing in a MethodInterceptor to serve as the callback). So when the MethodInterceptor's intercept method is called, that's where I'm trying to determine the name and return type of the Groovy method that was intercepted. I'll try grabbing some more debug output... – Jonathan Aug 22 '13 at 05:00
  • Then, if you're doing something like in the cglib examples, and then calling getName() directly, I'm quite sure that what is happening is what I put in my answer. – Alfergon Aug 22 '13 at 08:38
  • Updated the OP with a call stack. – Jonathan Aug 23 '13 at 22:50