remoteexporter.java

Java/J2EE application framework based on [Expert One-on-One J2EE Design and Development] by Rod John

/*
 * Copyright 2002-2004 the original author or authors.
 * 
 * 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 org.springframework.remoting.support;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.aop.framework.ProxyFactory;

/**
 * Abstract base class for classes that export a remote service.
 * Provides "service" and "serviceInterface" bean properties.
 *
 * <p>Note that the service interface being used will show some signs of
 * remotability, like the granularity of method calls that it offers.
 * Furthermore, it has to have serializable arguments etc.
 *
 * @author Juergen Hoeller
 * @since 26.12.2003
 */
public abstract class RemoteExporter {

	protected final Log logger = LogFactory.getLog(getClass());

	private Object service;

	private Class serviceInterface;


	/**
	 * Set the service to export.
	 * Typically populated via a bean reference.
	 */
	public void setService(Object service) {
		this.service = service;
	}

	/**
	 * Return the service to export.
	 */
	protected Object getService() {
		return service;
	}

	/**
	 * Set the interface of the service to export.
	 * The interface must be suitable for the particular service and remoting tool.
	 */
	public void setServiceInterface(Class serviceInterface) {
		if (serviceInterface != null && !serviceInterface.isInterface()) {
			throw new IllegalArgumentException("serviceInterface must be an interface");
		}
		this.serviceInterface = serviceInterface;
	}

	/**
	 * Return the interface of the service to export.
	 */
	protected Class getServiceInterface() {
		return serviceInterface;
	}


	/**
	 * Check whether the service reference has been set.
	 * @see #setService
	 */
	protected void checkService() throws IllegalArgumentException {
		if (this.service == null) {
			throw new IllegalArgumentException("service is required");
		}
	}

	/**
	 * Check whether a service reference has been set,
	 * and whether it matches the specified service.
	 * @see #setServiceInterface
	 * @see #setService
	 */
	protected void checkServiceInterface() throws IllegalArgumentException {
		if (this.serviceInterface == null) {
			throw new IllegalArgumentException("serviceInterface is required");
		}
		if (!this.serviceInterface.isInstance(this.service)) {
			throw new IllegalArgumentException(
					"serviceInterface [" + this.serviceInterface.getName() +
					"] needs to be implemented by service [" + this.service + "]");
		}
	}

	/**
	 * Get a proxy for the given service object, implementing the specified
	 * service interface.
	 * <p>Used to export a proxy that does not expose any internals but just
	 * a specific interface intended for remote access. Typically only applied
	 * if the remoting tool itself does not offer such means itself.
	 * @return the proxy
	 * @see #setServiceInterface
	 */
	protected Object getProxyForService() {
		checkService();
		checkServiceInterface();
		ProxyFactory proxyFactory = new ProxyFactory();
		proxyFactory.addInterface(getServiceInterface());
		proxyFactory.setTarget(getService());
		return proxyFactory.getProxy();
	}

}