/*****************************************************************************
* Licensed to the Apache Software Foundation (ASF) under one *
* or more contributor license agreements. See the NOTICE file *
* distributed with this work for additional information *
* regarding copyright ownership. The ASF licenses this file *
* to you under the Apache License, Version 2.0 (the *
* "License"); you may not use this file except in compliance *
* with the License. You may obtain a copy of the License at *
* *
* http://www.apache.org/licenses/LICENSE-2.0 *
* *
* Unless required by applicable law or agreed to in writing, *
* software distributed under the License is distributed on an *
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY *
* KIND, either express or implied. See the License for the *
* specific language governing permissions and limitations *
* under the License. *
* *
* *
* This file is part of the BeanShell Java Scripting distribution. *
* Documentation and updates may be found at http://www.beanshell.org/ *
* Patrick Niemeyer (pat@pat.net) *
* Author of Learning Java, O'Reilly & Associates *
* *
*****************************************************************************/
package bsh;
import java.lang.reflect.*;
import java.lang.reflect.
InvocationHandler;
import java.io.*;
import java.util.
Hashtable;
/**
XThis is a dynamically loaded extension which extends This.java and adds
support for the generalized interface proxy mechanism introduced in
JDK1.3. XThis allows bsh scripted objects to implement arbitrary
interfaces (be arbitrary event listener types).
Note: This module relies on new features of JDK1.3 and will not compile
with JDK1.2 or lower. For those environments simply do not compile this
class.
Eventually XThis should become simply This, but for backward compatibility
we will maintain This without requiring support for the proxy mechanism.
XThis stands for "eXtended This" (I had to call it something).
@see JThis See also JThis with explicit JFC support for compatibility.
@see This
*/
public class
XThis extends
This
{
/**
A cache of proxy interface handlers.
Currently just one per interface.
*/
Hashtable interfaces;
transient
InvocationHandler invocationHandler = new
Handler();
public
XThis(
NameSpace namespace,
Interpreter declaringInterp ) {
super(
namespace,
declaringInterp );
}
public
String toString() {
return "'this' reference (XThis) to Bsh object: " +
namespace;
}
/**
Get dynamic proxy for interface, caching those it creates.
*/
public
Object getInterface(
Class clas )
{
return
getInterface( new
Class[] {
clas } );
}
/**
Get dynamic proxy for interface, caching those it creates.
*/
public
Object getInterface(
Class []
ca )
{
if (
interfaces == null )
interfaces = new
Hashtable();
// Make a hash of the interface hashcodes in order to cache them
int
hash = 21;
for(int
i=0;
i<
ca.length;
i++)
hash *=
ca[
i].
hashCode() + 3;
Object hashKey = new
Integer(
hash);
Object interf =
interfaces.
get(
hashKey );
if (
interf == null )
{
ClassLoader classLoader =
ca[0].
getClassLoader(); // ?
interf =
Proxy.
newProxyInstance(
classLoader,
ca,
invocationHandler );
interfaces.
put(
hashKey,
interf );
}
return
interf;
}
/**
This is the invocation handler for the dynamic proxy.
<p>
Notes:
Inner class for the invocation handler seems to shield this unavailable
interface from JDK1.2 VM...
I don't understand this. JThis works just fine even if those
classes aren't there (doesn't it?) This class shouldn't be loaded
if an XThis isn't instantiated in NameSpace.java, should it?
*/
class
Handler implements
InvocationHandler
{
private
Object readResolve() throws
ObjectStreamException {
throw new
NotSerializableException();
}
public
Object invoke(
Object proxy,
Method method,
Object[]
args )
throws
Throwable
{
try {
return
invokeImpl(
proxy,
method,
args );
} catch (
TargetError te ) {
// Unwrap target exception. If the interface declares that
// it throws the ex it will be delivered. If not it will be
// wrapped in an UndeclaredThrowable
throw
te.
getTarget();
} catch (
EvalError ee ) {
// Ease debugging...
// XThis.this refers to the enclosing class instance
if (
Interpreter.
DEBUG )
Interpreter.
debug( "EvalError in scripted interface: "
+
XThis.this.
toString() + ": "+
ee );
throw
ee;
}
}
public
Object invokeImpl(
Object proxy,
Method method,
Object[]
args )
throws
EvalError
{
String methodName =
method.
getName();
CallStack callstack = new
CallStack(
namespace );
/*
If equals() is not explicitly defined we must override the
default implemented by the This object protocol for scripted
object. To support XThis equals() must test for equality with
the generated proxy object, not the scripted bsh This object;
otherwise callers from outside in Java will not see a the
proxy object as equal to itself.
*/
BshMethod equalsMethod = null;
try {
equalsMethod =
namespace.
getMethod(
"equals", new
Class [] {
Object.class } );
} catch (
UtilEvalError e ) {/*leave null*/ }
if (
methodName.
equals("equals" ) &&
equalsMethod == null ) {
Object obj =
args[0];
return
proxy ==
obj ?
Boolean.
TRUE :
Boolean.
FALSE;
}
/*
If toString() is not explicitly defined override the default
to show the proxy interfaces.
*/
BshMethod toStringMethod = null;
try {
toStringMethod =
namespace.
getMethod( "toString", new
Class [] { } );
} catch (
UtilEvalError e ) {/*leave null*/ }
if (
methodName.
equals("toString" ) &&
toStringMethod == null)
{
Class []
ints =
proxy.
getClass().
getInterfaces();
// XThis.this refers to the enclosing class instance
StringBuffer sb = new
StringBuffer(
XThis.this.
toString() + "\nimplements:" );
for(int
i=0;
i<
ints.length;
i++)
sb.
append( " "+
ints[
i].
getName()
+ ((
ints.length > 1)?",":"") );
return
sb.
toString();
}
Class []
paramTypes =
method.
getParameterTypes();
return
Primitive.
unwrap(
invokeMethod(
methodName,
Primitive.
wrap(
args,
paramTypes) ) );
}
};
}