org.jdal.util.concurrent.DispatcherQueue.java Source code

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/*
 * Copyright 2009-2012 Jose Luis Martin.
 *
 * 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.jdal.util.concurrent;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.Executor;
import java.util.concurrent.LinkedBlockingQueue;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.core.task.SyncTaskExecutor;

/**
 * Wrapper for a BlockingQueue that dispatchs incoming objets to a Task Executor.
 * You need to configure a Dispatcher or override dispatch(T t) mehod.   
 * 
 * @author Jose Luis Martin
 * @param <T> Objetc type stored in Queue.
 * @since 1.3
 */
public class DispatcherQueue<T> {

    private static final Log log = LogFactory.getLog(DispatcherQueue.class);
    private BlockingQueue<T> queue = new LinkedBlockingQueue<T>();
    private Thread dispatcherThread;
    /** true when dispatching messages */
    private volatile boolean running = false;
    /** Task executor to execute Dispatchers as Runnables */
    private Executor executor = new SyncTaskExecutor();
    /** Dispatcher instance */
    private Dispatcher<T> dispatcher;

    public DispatcherQueue() {

    }

    public DispatcherQueue(Dispatcher<T> dispatcher) {
        this.dispatcher = dispatcher;
    }

    /**
     * Create and start dispatcher thread
     */
    public void init() {
        start();
    }

    /**
     * Dispatch incomming objects to a Executor
     */
    private void dispatch() {
        while (running) {
            T t = null;
            try {
                t = queue.take();

                if (log.isDebugEnabled())
                    log.debug("Dispatching object: " + t.toString());

                dispatcher.dispatch(t);

            } catch (InterruptedException e) {
                log.error(e);
                break;
            } catch (Exception e) {
                log.error("Dispather failed. Readding object to queue again.");
                log.error(e.getMessage());
                queue.offer(t);
            }
        }
    }

    /**
     * Create a Runnable to dispatch incomming messages
     * @param msg message to be dispatched
     * @return Runnable
     */
    protected Runnable createWorker(final T t) {
        return new Runnable() {
            public void run() {
                dispatch(t);
            }
        };
    }

    /**
     * Dispatch objects in Queue
     * @param msg 
     */
    protected void dispatch(T t) {
        if (dispatcher != null) {
            try {
                dispatcher.dispatch(t);
            } catch (Exception e) {
                log.error(e);
            }
        } else {
            log.error("Dispatcher is null, Override default dispatch method or " + "configure a dispatcher.");
        }
    }

    /**
     * Gets the number of messages on the queue.
     * @return queue size
     * @see java.util.Collection#size()
     */
    public int size() {
        return queue.size();
    }

    /**
     * Insert a Object to the queue, waiting if necessary.
     * @param t object to put on queue
     * @see java.util.concurrent.BlockingQueue#put(java.lang.Object)
     */
    public void put(T t) {
        try {
            queue.put(t);
        } catch (InterruptedException e) {
            log.error(e);
        }
    }

    /**
     * Clear all messages on the queue
     * @see java.util.Collection#clear()
     */
    public void clear() {
        queue.clear();
    }

    /** 
     * Stop Dispatcher
     */
    public void stop() {
        running = false;
        dispatcherThread.interrupt();
        try {
            dispatcherThread.join();
        } catch (InterruptedException e) {
            log.error(e);
        }
    }

    public void start() {
        if (running) {
            log.warn("Already running");
            return;
        }

        dispatcherThread = new Thread(new Runnable() {
            public void run() {
                dispatch();
            }
        });

        running = true;
        log.info("Starting dispatcher thread");
        dispatcherThread.start();
    }

    /**
     * @return the dispatcher
     */
    public Dispatcher<T> getDispatcher() {
        return dispatcher;
    }

    /**
     * @param dispatcher the dispatcher to set
     */
    public void setDispatcher(Dispatcher<T> dispatcher) {
        this.dispatcher = dispatcher;
    }

    /**
     * @return the queue
     */
    public BlockingQueue<T> getQueue() {
        return queue;
    }

    /**
     * @param queue the queue to set
     */
    public void setQueue(BlockingQueue<T> queue) {
        this.queue = queue;
    }

    /**
     * @return the running
     */
    public boolean isRunning() {
        return running;
    }

    /**
     * @param running the running to set
     */
    public void setRunning(boolean running) {
        this.running = running;
    }

    /**
     * @return the executor
     */
    public Executor getExecutor() {
        return executor;
    }

    /**
     * @param executor the executor to set
     */
    public void setExecutor(Executor executor) {
        this.executor = executor;
    }

    public interface Dispatcher<T> {
        void dispatch(T t);
    }
}