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Dynamic method invocation

 
 
jythonuser
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      06-23-2009
Hi
I am new to jythong and was wondering if/how I can do the following -

a) register a java object with a given name with jython interpreter
using set method
b) call methods on the java object - but the methods may not exist on
the object, so I would like to call from jython a generic method that
I have defined on the object as opposed to using java reflection.
Thus the java class is more like a proxy for invocation.

As an example, I register an instance of java class Bar with name
foo. I want to be able to call from jython -
foo.method1 (args)
I don't want to define all the methods that I can call from jython on
class foo but have a generic method that the above jython code will
invoke. I want to use a model where the methods that can be called on
foo are discovered dynamically once they are invoked on java class.
Clearly Java won't let me do this during method invocation so I am
wondering if I can register some sort of proxy object with jython that
will let me then delegate right call down to the java object.

Thanks a bunch

 
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Diez B. Roggisch
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      06-23-2009
jythonuser schrieb:
> Hi
> I am new to jythong and was wondering if/how I can do the following -
>
> a) register a java object with a given name with jython interpreter
> using set method
> b) call methods on the java object - but the methods may not exist on
> the object, so I would like to call from jython a generic method that
> I have defined on the object as opposed to using java reflection.
> Thus the java class is more like a proxy for invocation.
>
> As an example, I register an instance of java class Bar with name
> foo. I want to be able to call from jython -
> foo.method1 (args)
> I don't want to define all the methods that I can call from jython on
> class foo but have a generic method that the above jython code will
> invoke. I want to use a model where the methods that can be called on
> foo are discovered dynamically once they are invoked on java class.
> Clearly Java won't let me do this during method invocation so I am
> wondering if I can register some sort of proxy object with jython that
> will let me then delegate right call down to the java object.


It's very unclear to me what you want, but to me, it looks as if you
have some misconceptions about jython.

There is no "registration" of java-objects. If you have a java-object,
you can assign it to a name, and simply invoke any method on it
(internally, that will mean using reflection, but that's below the
covers for you)

foo = SomeJavaClass()
foo.some_method()

As long as some_method is defined on SomeJavaClass, this will work. And
there is also no type-information needed, so this will work in Jython,
but not in java:


---- java ----

class A {
public void foo() {};
}

class B { // NOT A SUBCLASS OF A!!
public void foo() {};
}


---- jython ----

if some_condition:
bar = A()
else:
bar = B()

bar.foo()



Regarding the "generic method thing", I guess this will work:


foo = SomeJavaObject()

m = getattr(foo, "method_name_that_might_not_be_defined", None)

if m:
m(argument)


Diez
 
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jythonuser
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      06-26-2009
Sorry for being a little vague. The last part of your response seems
like what I would need. So here are more details on what I am trying
to do.

I have an extensible command shell in java where commmand providers
plug in to supply new commands. I have a java class called MyShell
which has execCommand method on it. Thus MyShell class does not have
a concrete method on it for each command that it supports (e.g. grep,
ls, cat etc) but a generic execCommand method that takes the name of
the command and command params as arguments.

clas MyShell () {
Object execCommand (cmdName, params) {
Object o = // find command object from command name
return o.invoke (cmdName, params);
}
|

Now I want to use this in jython. So I could do something like
shell = MyShell()
shell.exec ("grep", grep_args)

What I would like to do is -
shell.grep (grep_args)

That way my users don't have to use some gorpy exec/invoke syntax for
each command but think that shell has all the commands defined on it.
So based on your example I am hoping that I can use getattr on "some"
object that returns me "some" method that I can call.

Does this make sense and is there a way to do this in jython?
 
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jythonuser
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      06-26-2009
Actually let me add that in jython I don't need to always use
MyShell. It may be ok to wrapper it with some Jython class which then
delegates to MyShell. So something like

shell = MyJythonShell()
shell.grep (grep_args)

So MyJythonShell is defined in Jython which calls MyShell.

Am wondering how to go about all this.
 
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