src/main/java/org/apache/commons/proxy/factory/javassist/JavassistInvocation.java

/*
 * 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.
 */

package org.apache.commons.proxy.factory.javassist;

import javassist.CannotCompileException;
import javassist.CtClass;
import javassist.CtConstructor;
import javassist.CtMethod;
import org.apache.commons.proxy.Invocation;
import org.apache.commons.proxy.ProxyUtils;

import java.lang.ref.WeakReference;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;

/**
 * @author James Carman
 * @since 1.0
 */
public abstract class JavassistInvocation implements Invocation
{
//----------------------------------------------------------------------------------------------------------------------
// Fields
//----------------------------------------------------------------------------------------------------------------------
    private static WeakHashMap loaderToClassCache = new WeakHashMap();
    protected final Method method;
    protected final Object target;
    protected final Object[] arguments;

//----------------------------------------------------------------------------------------------------------------------
// Static Methods
//----------------------------------------------------------------------------------------------------------------------

    private static String createCastExpression( Class type, String objectToCast )
    {
        if( !type.isPrimitive() )
        {
            return "( " + ProxyUtils.getJavaClassName( type ) + " )" + objectToCast;
        }
        else
        {
            return "( ( " + ProxyUtils.getWrapperClass( type ).getName() + " )" + objectToCast + " )." +
                   type.getName() + "Value()";
        }
    }

    private static Class createInvocationClass( ClassLoader classLoader, Method interfaceMethod )
            throws CannotCompileException
    {
        Class invocationClass;
        final CtClass ctClass = JavassistUtils.createClass(
                getSimpleName( interfaceMethod.getDeclaringClass() ) + "_" + interfaceMethod.getName() +
                "_invocation",
                JavassistInvocation.class );
        final CtConstructor constructor = new CtConstructor(
                JavassistUtils.resolve( new Class[]{ Method.class, Object.class, Object[].class } ),
                ctClass );
        constructor.setBody( "{\n\tsuper($$);\n}" );
        ctClass.addConstructor( constructor );
        final CtMethod proceedMethod = new CtMethod( JavassistUtils.resolve( Object.class ), "proceed",
                                                     JavassistUtils.resolve( new Class[0] ), ctClass );
        final Class[] argumentTypes = interfaceMethod.getParameterTypes();
        final StringBuffer proceedBody = new StringBuffer( "{\n" );
        if( !Void.TYPE.equals( interfaceMethod.getReturnType() ) )
        {
            proceedBody.append( "\treturn " );
            if( interfaceMethod.getReturnType().isPrimitive() )
            {
                proceedBody.append( "new " );
                proceedBody.append( ProxyUtils.getWrapperClass( interfaceMethod.getReturnType() ).getName() );
                proceedBody.append( "( " );
            }
        }
        else
        {
            proceedBody.append( "\t" );
        }
        proceedBody.append( "( (" );
        proceedBody.append( ProxyUtils.getJavaClassName( interfaceMethod.getDeclaringClass() ) );
        proceedBody.append( " )target )." );
        proceedBody.append( interfaceMethod.getName() );
        proceedBody.append( "(" );
        for( int i = 0; i < argumentTypes.length; ++i )
        {
            final Class argumentType = argumentTypes[i];
            proceedBody.append( createCastExpression( argumentType, "arguments[" + i + "]" ) );
            if( i != argumentTypes.length - 1 )
            {
                proceedBody.append( ", " );
            }
        }
        if( !Void.TYPE.equals( interfaceMethod.getReturnType() ) && interfaceMethod.getReturnType().isPrimitive() )
        {
            proceedBody.append( ") );\n" );
        }
        else
        {
            proceedBody.append( ");\n" );
        }
        if( Void.TYPE.equals( interfaceMethod.getReturnType() ) )
        {
            proceedBody.append( "\treturn null;\n" );
        }
        proceedBody.append( "}" );
        final String body = proceedBody.toString();
        proceedMethod.setBody( body );
        ctClass.addMethod( proceedMethod );
        invocationClass = ctClass.toClass( classLoader );
        return invocationClass;
    }

    private static Map getClassCache( ClassLoader classLoader )
    {
        Map cache = ( Map ) loaderToClassCache.get( classLoader );
        if( cache == null )
        {
            cache = new HashMap();
            loaderToClassCache.put( classLoader, cache );
        }
        return cache;
    }

    public synchronized static Class getMethodInvocationClass( ClassLoader classLoader,
                                                               Method interfaceMethod )
            throws CannotCompileException
    {
        final Map classCache = getClassCache( classLoader );
        final String key = toClassCacheKey( interfaceMethod );
        final WeakReference invocationClassRef = ( WeakReference ) classCache.get( key );
        Class invocationClass;
        if( invocationClassRef == null )
        {
            invocationClass = createInvocationClass( classLoader, interfaceMethod );
            classCache.put( key, new WeakReference( invocationClass ) );
        }
        else
        {
            synchronized( invocationClassRef )
            {
                invocationClass = ( Class ) invocationClassRef.get();
                if( invocationClass == null )
                {
                    invocationClass = createInvocationClass( classLoader, interfaceMethod );
                    classCache.put( key, new WeakReference( invocationClass ) );
                }
            }
        }
        return invocationClass;
    }

    private static String getSimpleName( Class c )
    {
        final String name = c.getName();
        final int ndx = name.lastIndexOf( '.' );
        return ndx == -1 ? name : name.substring( ndx + 1 );
    }

    private static String toClassCacheKey( Method method )
    {
        return String.valueOf( method );
    }

//----------------------------------------------------------------------------------------------------------------------
// Constructors
//----------------------------------------------------------------------------------------------------------------------

    public JavassistInvocation( Method method, Object target, Object[] arguments )
    {
        this.method = method;
        this.target = target;
        this.arguments = arguments;
    }

//----------------------------------------------------------------------------------------------------------------------
// Invocation Implementation
//----------------------------------------------------------------------------------------------------------------------

    public Object[] getArguments()
    {
        return arguments;
    }

    public Method getMethod()
    {
        return method;
    }

    public Object getProxy()
    {
        return target;
    }
}