[3096] in java-interest
Re: dynamic method invocation -- any more discussion?
daemon@ATHENA.MIT.EDU (Steve V. Yalovitser)
Mon Oct 30 21:00:49 1995
From: "Steve V. Yalovitser" <root@cyberpunk.com>
In-Reply-To: <9510301605.AA01854@m-space.com>
To: java-interest@java.sun.com
Cc: Chris Cuilla <ccuilla@m-space.com>
Date: Mon, 30 Oct 1995 19:09:59 +0800 (EST)
Dynamic method invocation was relatively simple to hack up for the simple
case. There was an old mail by Tom Ball or Arthur which gave a blueprint. It isnt
really correct but should give a start:
From daemon@java.sun.com Tue Sep 26 09:37 EDT 1995
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Date: Mon, 25 Sep 1995 10:26:28 -0700
From: cmcmanis@scndprsn.Eng.Sun.COM (Chuck McManis)
Message-Id: <9509251726.AA16926@pepper.Eng.Sun.COM>
To: gbolcer@liege.ICS.UCI.EDU, mikec@metronet.com
Subject: Re: Dynamic Loading of Classes
Cc: java-interest@java.Eng.Sun.COM
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>In article Gregory Alan Bolcer <gbolcer@liege.ICS.UCI.EDU> writes:
>> I've programmed myself into a corner, and I am seeking advice
>>on the following problem. I have a Java unix process that is
>>maintaining a dynamically changeable object model (categories)
>>built on top of Java. The methods to these categories can be
>>dynamically changed at runtime and are implemented as Java classes
>>within a file directory.
Mike Responds...
>Sounds cool however, Java is not a dynamic language in the sense that
>Smalltalk is a dynamic language. This works it self back to the request for
>perform: capabilities ala Smalltalk. The reason for no perform: (as it was
>explained to me) is that it opens a big security hole. For example, a Nasty
>Old Java App (NOJA) could evoke the method "MySystem.sendUglyMailToMyBoss"
if
>a class with such an interface exists. I guess that the NOJA could scan the
>class which it finds on a given workstation and try things at random causing
>all sorts of havoc.
Mike is correct, however if your already running UNIX processes then
you are not an applet and just a Java ap. Consider writing your own
"perform" class, to do some (most?) of it is fairly trivial.
NOTES: THE FOLLOWING CODE IS WRITTEN "on the fly" And probably won't
even compile, much less work, however it should provide sufficient
information to do what you want.
Write a class "DynamicMethodInvoker" which is defined something like:
class DynamicMethodInvoker {
static {System.loadLibrary("dynamix");}
private native Object executeDynamicMethod(Object o, String meth,
String sig, Object args[]);
public Object doDynamicMethod(Object o, String meth, String sig,
Object args[]) {
/* Implement some security policy here. Maybe call SecurityManger
canInvoke or something you make up, what ever you do, don't
let applets call this. */
SecurityManager.mySecurityPolicy();
return (executeDynamicMethod(o,meth, sig, args));
}
}
And in the C code write:
int parseSignature(char *sig) {
static char *cursig;
if (sig != NULL) {
cursig = sig; /* set the signature */
cursig = strchar(sig, '['); /* find the arguments */
return 0;
}
return (getnextparameter(cursig)); /* return next argument type
(int, object ref, etc) */
}
int sigComponents(char *sig) {
/* return number of arguments to the method */
}
ClassDynamicMethodInvoker_executeDynamicMethod(HObject *this,
HObject *that, HString *meth, HString *sig, HArrayOfObject *args) {
long res;
switch (sigComponents(sig)) {
case 0:
res = java_execute_dynamic_method(getEE(), unhand (that),
unhand(meth), unhand(sig));
break;
case 1:
parseSignature(sig);
res = java_execute_dynamic_method(getEE(), unhand (that),
unhand(meth), unhand(sig),getnextParameter(sig));
break;
...
/* repeat for as many arguments as you would like. */
}
type = parsesignatureResult(sig);
/* this should simply parse the return type. */
/* if it is a simple type (int, long, etc) then call
execute_java_constructor() on the result with the
simple type's class
(ie execute_java_constructor(..,"Integer", res,...)
*/
return res;
}
Note that amateur spelunkers should not try to do this, it will just
confuse you.
--Chuck
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