Create an instance of org.apache.thrift.TProcessor bound to the classes at run time

TProcessors.java

/* TProcessors.java
 * Create an instance of org.apache.thrift.TProcessor bound to the classes at run time.
 * TProcessor processor = TProcessors.newInstance(Class.forName(className), Class.forName(serviceName));
 * 
 * Copyright (C) 2011 TAKUMAKei
 *
 * Licensed 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 com.blogspot.takumakei.gist;

import java.util.HashSet;

import org.apache.thrift.TProcessor;

/**
 * Utility class for Apache Thrift.
 * 
 * Create an instance of org.apache.thrift.TProcessor bound to the classes at run time.<p>
 *
 * You can easily create an instance of TProcessor like below.<p>
 * <code>
 * TProcessor processor = Processors.newInstance(Implementation.class);
 * </code><p>
 * 
 * The code above creates an equivalent processor instance like below.<p>
 * <code>
 * TProcessor processor = new GeneratedServiceClass.Processor<GeneratedServiceClass.Iface>(new Implementation());
 * </code><p>
 *
 * You can also specify the GeneratedServiceClass.
 * This feature is needed in case of that your implementation class implements multiple Iface.<p>
 * <code>
 * TProcessor processor = Processors.newInstance(Implementation.class, GeneratedServiceClass.class);
 * </code><p>
 * 
 * These features allows you to write the code below.<p>
 * <code>
 * TProcessor processor = TProcessors.newInstance(Class.forName(className), Class.forName(serviceName));
 * </code><p>
 * 
 * The real purpose of this class is to achieve the ability to write in this way.<p>
 */
public class TProcessors {
	/**
	 * Create an instance of Processor, which wraps a new instance of targetClass.
	 */
	public static TProcessor newInstance(Class<?> targetClass) {
		return newInstance(newTarget(targetClass));
	}

	/**
	 * Create an instance of Processor, which wraps the target object.
	 */
	public static TProcessor newInstance(Object target) {
		HashSet<Class<?>> ifaces = findIfaces(target.getClass(), new HashSet<Class<?>>());
		if (ifaces.isEmpty()) {
			throw new IllegalArgumentException(
					target.getClass().getName() + " must implement Iface");
		}
		return newProcessor(target, ifaces.iterator().next());
	}

	/**
	 * Create an instance of Processor, which wraps a new instance of targetClass.
	 * @param serviceClass the Iface class or the service class enclosing the Iface class.
	 */
	public static TProcessor newInstance(Class<?> targetClass, Class<?> serviceClass) {
		return newInstance(newTarget(targetClass), serviceClass);
	}

	/**
	 * Create an instance of Processor, which wraps the target object.
	 * @param serviceClass the Iface class or the service class enclosing the Iface class.
	 */
	public static TProcessor newInstance(Object target, Class<?> serviceClass) {
		if (null == serviceClass) {
			return newInstance(target);
		}
		for (Class<?> iface : findIfaces(target.getClass(), new HashSet<Class<?>>())) {
			if (iface.getEnclosingClass() == serviceClass || iface == serviceClass) {
				return newProcessor(target, iface);
			}
		}
		throw new IllegalArgumentException(
				target.getClass().getName() + " does not implement " + serviceClass.getName());
	}

	protected static Object newTarget(Class<?> targetClass) {
		try {
			return targetClass.newInstance();
		} catch (Exception e) {
			throw new IllegalArgumentException(
					"Failed to create an instance of " + targetClass.getName(), e);
		}
	}

	protected static HashSet<Class<?>> findIfaces(Class<?> targetClass, HashSet<Class<?>> ifaces) {
		if (targetClass == Object.class) {
			return ifaces;
		}
		for (Class<?> iface : targetClass.getInterfaces()) {
			if ("Iface".equals(iface.getSimpleName())) {
				for (Class<?> processorClass : iface.getEnclosingClass().getClasses()) {
					if (TProcessor.class.isAssignableFrom(processorClass)) {
						ifaces.add(iface);
						break;
					}
				}
			}
		}
		return findIfaces(targetClass.getSuperclass(), ifaces);
	}

	protected static TProcessor newProcessor(Object target, Class<?> ifaceClass) {
		try {
			for (Class<?> processorClass : ifaceClass.getEnclosingClass().getClasses()) {
				if (TProcessor.class.isAssignableFrom(processorClass)) {
					return (TProcessor) processorClass.getConstructor(ifaceClass).newInstance(target);
				}
			}
		} catch (Exception e) {
			throw new IllegalArgumentException(
					"Failed to create an instance of Processor for " + ifaceClass.getName(), e);
		}
		throw new IllegalArgumentException("No Processor class found for " + ifaceClass.getName());
	}
}