/jEdit/tags/jedit-4-1-pre5/bsh/XThis.java

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 *  Patrick Niemeyer (pat@pat.net)                                           *
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 *  http://www.pat.net/~pat/                                                 *
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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 compatability
	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 compatability.
	@see This	
*/
class XThis extends This 
	{
	/**
		A cache of proxy interface handlers.
		Currently just one per interface.
	*/
	Hashtable interfaces;

	InvocationHandler invocationHandler = new Handler();

	XThis( NameSpace namespace, Interpreter declaringInterp ) { 
		super( namespace, declaringInterp ); 
	}

	public String toString() {
		return "'this' reference (XThis) to Bsh object: " + namespace.name;
	}

	String toStringShowInts( Class [] ints ) {
		StringBuffer sb = new StringBuffer( toString() + "\nimplements:" );
		for(int i=0; i<ints.length; i++)
			sb.append( " "+ ints[i].getName() + ((ints.length > 1)?",":"") );
		return sb.toString();
	}

	/**
		Get dynamic proxy for interface, caching those it creates.
	*/
	public Object getInterface( Class clas ) {
		if ( interfaces == null )
			interfaces = new Hashtable();

		Object interf = interfaces.get( clas );
		if ( interf == null ) {
			interf = Proxy.newProxyInstance( clas.getClassLoader(), 
				new Class[] { clas }, invocationHandler );
			interfaces.put( clas, interf );
		}
		return interf;
	}

	/**
		Get a proxy interface for the specified XThis reference.
		This is a static utility method because the interpreter doesn't 
		currently allow access to direct methods of This objects.
		
	public static Object getInterface( XThis ths, Class interf ) { 
		return ths.getInterface( 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, java.io.Serializable 
	{
		public Object invoke( Object proxy, Method method, Object[] args ) 
			throws EvalError 
		{
			try { 
				return invokeImpl( proxy, method, args );
			} catch ( EvalError ee ) {
				// Ease debugging...
				Interpreter.debug( "EvalError in scripted interface: "
					+ XThis.this.toString() + ": "+ ee );
				throw ee;
			}
		}

		public Object invokeImpl( Object proxy, Method method, Object[] args ) 
			throws EvalError 
		{
			CallStack callstack = newCallStack();

			Class [] sig = Reflect.getTypes( args );
			BshMethod bmethod = 
				namespace.getMethod( method.getName(), sig );

			if ( bmethod != null )
				return Primitive.unwrap( 
					bmethod.invokeDeclaredMethod( 
					args, declaringInterpreter, callstack, null ) );

			// Look for the default handler
			bmethod = namespace.getMethod( "invoke", 
				new Class [] { null, null } );

			// Call script "invoke( String methodName, Object [] args );
			if ( bmethod != null )
				return Primitive.unwrap( 
					bmethod.invokeDeclaredMethod( 
					new Object [] { method.getName(), args }, 
					declaringInterpreter, callstack, null ) );

			/*
				implement the required part of the Object protocol:
					public int hashCode();
					public boolean equals(java.lang.Object);
					public java.lang.String toString();
				if these were not handled by scripted methods we must provide
				a default impl.
			*/
			// a default toString() that shows the interfaces we implement
			if ( method.getName().equals("toString" ) )
				return toStringShowInts( proxy.getClass().getInterfaces());

			// a default hashCode()
			if ( method.getName().equals("hashCode" ) )
				return new Integer(this.hashCode());

			// a default equals()
			if ( method.getName().equals("equals" ) ) {
				Object obj = args[0];
				return new Boolean( proxy == obj );
			}

			throw new EvalError("Bsh script method: "+ method.getName()
				+ " not found in namespace: "+ namespace.name );
		}
	};

}