Work Around for Unwanted MQTT Unsubscribe - proxy the client

IgnoreUnsubscribePahoClientFactory.java

/*
 * Copyright 2015 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 com.foo;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.eclipse.paho.client.mqttv3.IMqttToken;
import org.eclipse.paho.client.mqttv3.MqttAsyncClient;
import org.eclipse.paho.client.mqttv3.MqttException;

import org.springframework.aop.framework.ProxyFactoryBean;

/**
 * @author Gary Russell
 * @since 4.3
 *
 */
public class IgnoreUnsubscribePahoClientFactory extends DefaultMqttPahoClientFactory {

	private static final Log logger = LogFactory.getLog(IgnoreUnsubscribePahoClientFactory.class);

	private IMqttToken alwaysComplete;

	@Override
	public MqttAsyncClient getAsyncClientInstance(String uri, String clientId) throws MqttException {
		MqttAsyncClient asyncClientInstance = super.getAsyncClientInstance(uri, clientId);
		buildTokenIfNeeded();
		return proxy(asyncClientInstance);
	}

	private MqttAsyncClient proxy(MqttAsyncClient asyncClientInstance) {
		ProxyFactoryBean pfb = new ProxyFactoryBean();
		pfb.addAdvice(new MethodInterceptor() {

			@Override
			public Object invoke(MethodInvocation invocation) throws Throwable {
				if (invocation.getMethod().getName().equals("unsubscribe")) {
					logger.warn("Skipping unsubscribe");
					return alwaysComplete;
				}
				else {
					return invocation.proceed();
				}
			}

		});
		pfb.setProxyTargetClass(true);
		pfb.setTarget(asyncClientInstance);
		return (MqttAsyncClient) pfb.getObject();
	}

	private void buildTokenIfNeeded() {
		if (this.alwaysComplete != null) {
			return;
		}
		ProxyFactoryBean pfb = new ProxyFactoryBean();
		pfb.addAdvice(new MethodInterceptor() {

			@Override
			public Object invoke(MethodInvocation invocation) throws Throwable {
				return null;
			}

		});
		pfb.setInterfaces(IMqttToken.class);
		this.alwaysComplete = (IMqttToken) pfb.getObject();
	}

}