/jEdit/tags/jedit-4-3-pre5/bsh/This.java

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 *  Patrick Niemeyer (pat@pat.net)                                           *
 *  Author of Learning Java, O'Reilly & Associates                           *
 *  http://www.pat.net/~pat/                                                 *
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 *****************************************************************************/


package bsh;

import java.io.IOException;

/**
	'This' is the type of bsh scripted objects.
	A 'This' object is a bsh scripted object context.  It holds a namespace 
	reference and implements event listeners and various other interfaces.

	This holds a reference to the declaring interpreter for callbacks from
	outside of bsh.
*/
public class This implements java.io.Serializable, Runnable 
{
	/**
		The namespace that this This reference wraps.
	*/
	NameSpace namespace;

	/**
		This is the interpreter running when the This ref was created.
		It's used as a default interpreter for callback through the This
		where there is no current interpreter instance 
		e.g. interface proxy or event call backs from outside of bsh.
	*/
	transient Interpreter declaringInterpreter;

	/**
		getThis() is a factory for bsh.This type references.  The capabilities
		of ".this" references in bsh are version dependent up until jdk1.3.
		The version dependence was to support different default interface
		implementations.  i.e. different sets of listener interfaces which
		scripted objects were capable of implementing.  In jdk1.3 the 
		reflection proxy mechanism was introduced which allowed us to 
		implement arbitrary interfaces.  This is fantastic.

		A This object is a thin layer over a namespace, comprising a bsh object
		context.  We create it here only if needed for the namespace.

		Note: this method could be considered slow because of the way it 
		dynamically factories objects.  However I've also done tests where 
		I hard-code the factory to return JThis and see no change in the 
		rough test suite time.  This references are also cached in NameSpace.  
	*/
    static This getThis( 
		NameSpace namespace, Interpreter declaringInterpreter ) 
	{
		try {
			Class c;
			if ( Capabilities.canGenerateInterfaces() )
				c = Class.forName( "bsh.XThis" );
			else if ( Capabilities.haveSwing() )
				c = Class.forName( "bsh.JThis" );
			else
				return new This( namespace, declaringInterpreter );

			return (This)Reflect.constructObject( c,
				new Object [] { namespace, declaringInterpreter } );

		} catch ( Exception e ) {
			throw new InterpreterError("internal error 1 in This: "+e);
		}
    }

	/**
		Get a version of this scripted object implementing the specified 
		interface.
	*/
	/*
		If this type of This implements it directly return this,
		else try complain that we don't have the proxy mechanism.
	*/
	public Object getInterface( Class clas ) 
		throws UtilEvalError
	{
		if ( clas.isInstance( this ) )
			return this;
		else
			throw new UtilEvalError( "Dynamic proxy mechanism not available. "
			+ "Cannot construct interface type: "+clas );
	}

	/**
		Get a version of this scripted object implementing the specified
		interfaces.
	*/
	public Object getInterface( Class [] ca ) 
		throws UtilEvalError
	{
		for(int i=0; i<ca.length; i++)
			if ( !(ca[i].isInstance( this )) )
				throw new UtilEvalError( 
					"Dynamic proxy mechanism not available. " 
					+ "Cannot construct interface type: "+ca[i] );

		return this;
	}

	/*
		I wish protected access were limited to children and not also 
		package scope... I want this to be a singleton implemented by various
		children.  
	*/
	protected This( NameSpace namespace, Interpreter declaringInterpreter ) { 
		this.namespace = namespace; 
		this.declaringInterpreter = declaringInterpreter;
		//initCallStack( namespace );
	}

	public NameSpace getNameSpace() {
		return namespace;
	}

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

	public void run() {
		try {
			invokeMethod( "run", new Object[0] );
		} catch( EvalError e ) {
			declaringInterpreter.error(
				"Exception in runnable:" + e );
		}
	}

	/**
		Invoke specified method as from outside java code, using the 
		declaring interpreter and current namespace.
		The call stack will indicate that the method is being invoked from
		outside of bsh in native java code.
		Note: you must still wrap/unwrap args/return values using 
		Primitive/Primitive.unwrap() for use outside of BeanShell.
		@see bsh.Primitive
	*/
	public Object invokeMethod( String name, Object [] args ) 
		throws EvalError
	{
		// null callstack, one will be created for us 
		return invokeMethod( 
			name, args, null/*declaringInterpreter*/, null, null, 
			false/*declaredOnly*/ );
	}

	/**
		Invoke a method in this namespace with the specified args,
		interpreter reference, callstack, and caller info.
		<p>

		Note: If you use this method outside of the bsh package and wish to 
		use variables with primitive values you will have to wrap them using 
		bsh.Primitive.  Consider using This getInterface() to make a true Java
		interface for invoking your scripted methods.
		<p>

		This method also implements the default object protocol of toString(), 
		hashCode() and equals() and the invoke() meta-method handling as a 
		last resort.
		<p>

		Note: The invoke() meta-method will not catch the Object protocol
		methods (toString(), hashCode()...).  If you want to override them you 
		have to script them directly.
		<p>

		@see bsh.This.invokeMethod( 
			String methodName, Object [] args, Interpreter interpreter, 
			CallStack callstack, SimpleNode callerInfo )
		@param if callStack is null a new CallStack will be created and
			initialized with this namespace.
		@param declaredOnly if true then only methods declared directly in the
			namespace will be visible - no inherited or imported methods will
			be visible.
		@see bsh.Primitive
	*/
	/*
		invokeMethod() here is generally used by outside code to callback
		into the bsh interpreter. e.g. when we are acting as an interface
		for a scripted listener, etc.  In this case there is no real call stack
		so we make a default one starting with the special JAVACODE namespace
		and our namespace as the next.
	*/
	public Object invokeMethod( 
		String methodName, Object [] args, 
		Interpreter interpreter, CallStack callstack, SimpleNode callerInfo, 
		boolean declaredOnly  ) 
		throws EvalError
	{
		/*
			Wrap nulls.
			This is a bit of a cludge to address a deficiency in the class
			generator whereby it does not wrap nulls on method delegate.  See
			Class Generator.java.  If we fix that then we can remove this.
			(just have to generate the code there.)
		*/
		if ( args != null )
		{
			Object [] oa = new Object [args.length];
			for(int i=0; i<args.length; i++)
				oa[i] = ( args[i] == null ? Primitive.NULL : args[i] );
			args = oa;
		}

		if ( interpreter == null )
			interpreter = declaringInterpreter;
		if ( callstack == null )
			callstack = new CallStack( namespace );
		if ( callerInfo == null )
			callerInfo = SimpleNode.JAVACODE;

		// Find the bsh method
		Class [] types = Types.getTypes( args );
		BshMethod bshMethod = null;
		try {
			bshMethod = namespace.getMethod( methodName, types, declaredOnly );
		} catch ( UtilEvalError e ) {
			// leave null
		}

		if ( bshMethod != null )
			return bshMethod.invoke( args, interpreter, callstack, callerInfo );

		/*
			No scripted method of that name.
			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 ( methodName.equals("toString" ) )
			return toString();

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

		// a default equals() testing for equality with the This reference
		if ( methodName.equals("equals" ) ) {
			Object obj = args[0];
			return new Boolean( this == obj );
		}

		// Look for a default invoke() handler method in the namespace
		// Note: this code duplicates that in NameSpace getCommand()
		// is that ok?
		try {
			bshMethod = namespace.getMethod( 
				"invoke", new Class [] { null, null } );
		} catch ( UtilEvalError e ) { /*leave null*/ }

		// Call script "invoke( String methodName, Object [] args );
		if ( bshMethod != null )
			return bshMethod.invoke( new Object [] { methodName, args }, 
				interpreter, callstack, callerInfo );

		throw new EvalError("Method " + 
			StringUtil.methodString( methodName, types ) +
			" not found in bsh scripted object: "+ namespace.getName(), 
			callerInfo, callstack );
	}

	/**
		Bind a This reference to a parent's namespace with the specified
		declaring interpreter.  Also re-init the callstack.  It's necessary 
		to bind a This reference before it can be used after deserialization.
		This is used by the bsh load() command.
		<p>

		This is a static utility method because it's used by a bsh command
		bind() and the interpreter doesn't currently allow access to direct 
		methods of This objects (small hack)
	*/
	public static void bind( 
		This ths, NameSpace namespace, Interpreter declaringInterpreter ) 
	{ 
		ths.namespace.setParent( namespace ); 
		ths.declaringInterpreter = declaringInterpreter;
	}

	/**
		Allow invocations of these method names on This type objects.
		Don't give bsh.This a chance to override their behavior.
		<p>

		If the method is passed here the invocation will actually happen on
		the bsh.This object via the regular reflective method invocation 
		mechanism.  If not, then the method is evaluated by bsh.This itself
		as a scripted method call.
	*/
	static boolean isExposedThisMethod( String name ) 
	{
		return 
			name.equals("getClass") 
			|| name.equals("invokeMethod")
			|| name.equals("getInterface")
			// These are necessary to let us test synchronization from scripts
			|| name.equals("wait") 
			|| name.equals("notify")
			|| name.equals("notifyAll");
	}

}