proxy-1.0-work/src/main/java/org/apache/commons/proxy/interceptor/ExecutorInterceptor.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.interceptor;

import EDU.oswego.cs.dl.util.concurrent.Executor;
import org.apache.commons.proxy.Invocation;
import org.apache.commons.proxy.Interceptor;

/**
 * A method interceptor that uses an {@link Executor} to execute the method invocation.
 * <p/>
 * <b>Note</b>: Only <em>void</em> methods can be intercepted using this class!  Any attempts to intercept non-void
 * methods will result in an {@link IllegalArgumentException}.  If the proxy interfaces include non-void methods, try
 * using a {@link FilteredInterceptor} along with a
 * {@link org.apache.commons.proxy.interceptor.filter.ReturnTypeFilter} to wrap an instance of this class.
 *
 * <p>
 * <b>Dependencies</b>:
 * <ul>
 *   <li>Concurrent API version 1.3.4 or greater</li>
 * </ul>
 * </p>
 * @author James Carman
 * @since 1.0
 */
public class ExecutorInterceptor implements Interceptor
{
    private final Executor executor;

    public ExecutorInterceptor( Executor executor )
    {
        this.executor = executor;
    }

    public Object intercept( final Invocation invocation ) throws Throwable
    {
        if( Void.TYPE.equals( invocation.getMethod().getReturnType() ) )
        {
            // Special case for finalize() method (should not be run in a different thread)...
            if( !( invocation.getMethod().getName().equals( "finalize" ) &&
                   invocation.getMethod().getParameterTypes().length == 0 ) )
            {
                executor.execute( new Runnable()
                {
                    public void run()
                    {
                        try
                        {
                            invocation.proceed();
                        }
                        catch( Throwable t )
                        {
                            // What to do here?  I can't convey the failure back to the caller.
                        }
                    }
                } );
                return null;
            }
            else
            {
                return invocation.proceed();
            }
        }
        else
        {
            throw new IllegalArgumentException( "Only void methods can be executed in a different thread." );
        }
    }
}