/jEdit/tags/jedit-4-2-pre14/bsh/XThis.java

  1/*****************************************************************************
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  3 *  This file is part of the BeanShell Java Scripting distribution.          *
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 11 *                                                                           *
 12 *  The Original Code is BeanShell. The Initial Developer of the Original    *
 13 *  Code is Pat Niemeyer. Portions created by Pat Niemeyer are Copyright     *
 14 *  (C) 2000.  All Rights Reserved.                                          *
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 28 *  Patrick Niemeyer (pat@pat.net)                                           *
 29 *  Author of Learning Java, O'Reilly & Associates                           *
 30 *  http://www.pat.net/~pat/                                                 *
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 33
 34
 35package bsh;
 36
 37import java.lang.reflect.*;
 38import java.lang.reflect.InvocationHandler;
 39import java.io.*;
 40import java.util.Hashtable;
 41
 42/**
 43	XThis is a dynamically loaded extension which extends This.java and adds 
 44	support for the generalized interface proxy mechanism introduced in 
 45	JDK1.3.  XThis allows bsh scripted objects to implement arbitrary 
 46	interfaces (be arbitrary event listener types).
 47
 48	Note: This module relies on new features of JDK1.3 and will not compile
 49	with JDK1.2 or lower.  For those environments simply do not compile this
 50	class.
 51
 52	Eventually XThis should become simply This, but for backward compatability
 53	we will maintain This without requiring support for the proxy mechanism.
 54
 55	XThis stands for "eXtended This" (I had to call it something).
 56	
 57	@see JThis	 See also JThis with explicit JFC support for compatability.
 58	@see This	
 59*/
 60class XThis extends This 
 61	{
 62	/**
 63		A cache of proxy interface handlers.
 64		Currently just one per interface.
 65	*/
 66	Hashtable interfaces;
 67
 68	InvocationHandler invocationHandler = new Handler();
 69
 70	XThis( NameSpace namespace, Interpreter declaringInterp ) { 
 71		super( namespace, declaringInterp ); 
 72	}
 73
 74	public String toString() {
 75		return "'this' reference (XThis) to Bsh object: " + namespace;
 76	}
 77
 78	/**
 79		Get dynamic proxy for interface, caching those it creates.
 80	*/
 81	public Object getInterface( Class clas ) 
 82	{
 83		return getInterface( new Class[] { clas } );
 84	}
 85
 86	/**
 87		Get dynamic proxy for interface, caching those it creates.
 88	*/
 89	public Object getInterface( Class [] ca ) 
 90	{
 91		if ( interfaces == null )
 92			interfaces = new Hashtable();
 93
 94		// Make a hash of the interface hashcodes in order to cache them
 95		int hash = 21;
 96		for(int i=0; i<ca.length; i++)
 97			hash *= ca[i].hashCode() + 3;
 98		Object hashKey = new Integer(hash);
 99
100		Object interf = interfaces.get( hashKey );
101
102		if ( interf == null ) 
103		{
104			ClassLoader classLoader = ca[0].getClassLoader(); // ?
105			interf = Proxy.newProxyInstance( 
106				classLoader, ca, invocationHandler );
107			interfaces.put( hashKey, interf );
108		}
109
110		return interf;
111	}
112
113	/**
114		This is the invocation handler for the dynamic proxy.
115		<p>
116
117		Notes:
118		Inner class for the invocation handler seems to shield this unavailable
119		interface from JDK1.2 VM...  
120		
121		I don't understand this.  JThis works just fine even if those
122		classes aren't there (doesn't it?)  This class shouldn't be loaded
123		if an XThis isn't instantiated in NameSpace.java, should it?
124	*/
125	class Handler implements InvocationHandler, java.io.Serializable 
126	{
127		public Object invoke( Object proxy, Method method, Object[] args ) 
128			throws Throwable
129		{
130			try { 
131				return invokeImpl( proxy, method, args );
132			} catch ( TargetError te ) {
133				// Unwrap target exception.  If the interface declares that 
134				// it throws the ex it will be delivered.  If not it will be 
135				// wrapped in an UndeclaredThrowable
136				throw te.getTarget();
137			} catch ( EvalError ee ) {
138				// Ease debugging...
139				// XThis.this refers to the enclosing class instance
140				if ( Interpreter.DEBUG ) 
141					Interpreter.debug( "EvalError in scripted interface: "
142					+ XThis.this.toString() + ": "+ ee );
143				throw ee;
144			}
145		}
146
147		public Object invokeImpl( Object proxy, Method method, Object[] args ) 
148			throws EvalError 
149		{
150			String methodName = method.getName();
151			CallStack callstack = new CallStack( namespace );
152
153			/*
154				If equals() is not explicitly defined we must override the 
155				default implemented by the This object protocol for scripted
156				object.  To support XThis equals() must test for equality with 
157				the generated proxy object, not the scripted bsh This object;
158				otherwise callers from outside in Java will not see a the 
159				proxy object as equal to itself.
160			*/
161			BshMethod equalsMethod = null;
162			try {
163				equalsMethod = namespace.getMethod( 
164					"equals", new Class [] { Object.class } );
165			} catch ( UtilEvalError e ) {/*leave null*/ }
166			if ( methodName.equals("equals" ) && equalsMethod == null ) {
167				Object obj = args[0];
168				return new Boolean( proxy == obj );
169			}
170
171			/*
172				If toString() is not explicitly defined override the default 
173				to show the proxy interfaces.
174			*/
175			BshMethod toStringMethod = null;
176			try {
177				toStringMethod = 
178					namespace.getMethod( "toString", new Class [] { } );
179			} catch ( UtilEvalError e ) {/*leave null*/ }
180
181			if ( methodName.equals("toString" ) && toStringMethod == null)
182			{
183				Class [] ints = proxy.getClass().getInterfaces();
184				// XThis.this refers to the enclosing class instance
185				StringBuffer sb = new StringBuffer( 
186					XThis.this.toString() + "\nimplements:" );
187				for(int i=0; i<ints.length; i++)
188					sb.append( " "+ ints[i].getName() 
189						+ ((ints.length > 1)?",":"") );
190				return sb.toString();
191			}
192
193			Class [] paramTypes = method.getParameterTypes();
194			return Primitive.unwrap( 
195				invokeMethod( methodName, Primitive.wrap(args, paramTypes) ) );
196		}
197	};
198}
199
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201