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Jetty example source code file (BayeuxService.java)

This example Jetty source code file (BayeuxService.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Jetty tags/keywords

bayeux, bayeuxservice, client, client, illegalargumentexception, listen, map, messagelistener, method, method, object, object, reflection, string, string, threading, threads, util

The Jetty BayeuxService.java source code

package org.mortbay.cometd;

import java.lang.reflect.Method;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import dojox.cometd.Bayeux;
import dojox.cometd.Channel;
import dojox.cometd.Client;
import dojox.cometd.Listener;
import dojox.cometd.Message;
import dojox.cometd.MessageListener;

/* ------------------------------------------------------------ */
/** Abstract Bayeux Service class.
 * This is a base class to assist with the creation of server side {@ link Bayeux} 
 * clients that provide services to remote Bayeux clients.   The class provides
 * a Bayeux {@link Client} and {@link Listener} together with convenience methods to map
 * subscriptions to methods on the derived class and to send responses to those methods.
 *
 * @author gregw
 *
 */
public abstract class BayeuxService 
{
    private String _name;
    private Bayeux _bayeux;
    private Client _client;
    private Map<String,Method> _methods = new ConcurrentHashMap();
    
    /* ------------------------------------------------------------ */
    /** Instantiate the service.
     * Typically the derived constructor will call {@ #subscribe(String, String)} to 
     * map subscriptions to methods.
     * @param bayeux The bayeux instance.
     * @param name The name of the service (used as client ID prefix).
     */
    public BayeuxService(Bayeux bayeux,String name)
    {
        _name=name;
        _bayeux=bayeux;
        _client=_bayeux.newClient(name);  
        _client.addListener(new Listen());
    }

    /* ------------------------------------------------------------ */
    public Bayeux getBayeux()
    {
        return _bayeux;
    }

    /* ------------------------------------------------------------ */
    public Client getClient()
    {
        return _client;
    }
    
    /* ------------------------------------------------------------ */
    /** Subscribe to a channel.
     * Subscribe to channel and map a method to handle received messages.
     * The method must have a unique name and one of the following signatures:<ul>
     * <li>myMethod(Client fromClient,Object data)
     * <li>myMethod(Client fromClient,Object data,String id)
     * <li>myMethod(Client fromClient,String channel,Object data,String id)
     * </li>
     * 
     * The data parameter can be typed if
     * the type of the data object published by the client is known (typically 
     * Map<String,Object>). If the type of the data parameter is {@link Message} then
     * the message object itself is passed rather than just the data.
     * <p>
     * Typically a service will subscribe to a channel in the "/service/**" space
     * which is not a broadcast channel.  Messages published to these channels are
     * only delivered to server side clients like this service.  
     * 
     * <p>Any object returned by a mapped subscription method is delivered to the 
     * calling client and not broadcast. If the method returns void or null, then 
     * no response is sent. A mapped subscription method may also call {@link #send(Client, String, Object, String)}
     * to deliver a response message(s) to different clients and/or channels. It may
     * also publish methods via the normal {@link Bayeux} API.
     * <p>
     * 
     * 
     * @param channelId The channel to subscribe to
     * @param methodName The name of the method on this object to call when messages are recieved.
     */
    protected void subscribe(String channelId,String methodName)
    {
        Method method=null;
        
        Class<?> c=this.getClass();
        while (c!=null && c!=Object.class)
        {
            Method[] methods = c.getDeclaredMethods();
            for (int i=methods.length;i-->0;)
            {
                if (methodName.equals(methods[i].getName()))
                {
                    if (method!=null)
                        throw new IllegalArgumentException("Multiple methods called '"+methodName+"'");
                    method=methods[i];
                }
            }
            c=c.getSuperclass();
        }
        
        if (method==null)
            throw new NoSuchMethodError(methodName);
        int params=method.getParameterTypes().length;
        if (params<2 || params>4)
            throw new IllegalArgumentException("Method '"+methodName+"' does not have 2or3 parameters");
        if (!Client.class.isAssignableFrom(method.getParameterTypes()[0]))
            throw new IllegalArgumentException("Method '"+methodName+"' does not have Client as first parameter");

        Channel channel=_bayeux.getChannel(channelId,true);

        if (((ChannelImpl)channel).getChannelId().isWild())
        { 
            final Method m=method;
            Client wild_client=_bayeux.newClient(_name+"-wild");
            wild_client.addListener(new MessageListener(){
                public void deliver(Client fromClient, Client toClient, Message msg)
                {
                    invoke(m,fromClient,toClient,msg);
                }
            });
            channel.subscribe(wild_client);
        }
        else
        {
            _methods.put(channelId,method);
            channel.subscribe(_client);
        }
    }

    /* ------------------------------------------------------------ */
    /** Send data to a individual client.
     * The data passed is sent to the client as the "data" member of a message
     * with the given channel and id.  The message is not published on the channel and is
     * thus not broadcast to all channel subscribers.  However to the target client, the
     * message appears as if it was broadcast.
     * <p>
     * Typcially this method is only required if a service method sends response(s) to 
     * channels other than the subscribed channel. If the response is to be sent to the subscribed
     * channel, then the data can simply be returned from the subscription method.
     * 
     * @param toClient The target client
     * @param onChannel The channel the message is for
     * @param data The data of the message
     * @param id The id of the message (or null for a random id).
     */
    protected void send(Client toClient, String onChannel, Object data, String id)
    {
        toClient.deliver(getClient(),onChannel,data,id);
    }    

    /* ------------------------------------------------------------ */
    /** Handle Exception.
     * This method is called when a mapped subscription method throws
     * and exception while handling a message.
     * @param fromClient
     * @param toClient
     * @param msg
     * @param th
     */
    protected void exception(Client fromClient, Client toClient, Map<String, Object> msg,Throwable th)
    {
        th.printStackTrace();
    }

    /* ------------------------------------------------------------ */
    private void deliver(Client fromClient, Client toClient, Map<String, Object> msg)
    {
        String channel=(String)msg.get(Bayeux.CHANNEL_FIELD);
        Method method=_methods.get(channel);
        invoke(method,fromClient,toClient,msg);
    }

    /* ------------------------------------------------------------ */
    private void invoke(Method method,Client fromClient, Client toClient, Map<String, Object> msg)
    {
        String channel=(String)msg.get(Bayeux.CHANNEL_FIELD);
        Object data=msg.get(Bayeux.DATA_FIELD);
        String id=(String)msg.get(Bayeux.ID_FIELD);
        if (method!=null)
        {
            try
            {
                Class<?>[] args = method.getParameterTypes();
                Object arg=Message.class.isAssignableFrom(args[1])?msg:data;
                
                Object reply=null;
                switch(method.getParameterTypes().length)
                {
                    case 2:
                        reply=method.invoke(this,fromClient,arg);
                        break;
                    case 3:
                        reply=method.invoke(this,fromClient,arg,id);
                        break;
                    case 4:
                        reply=method.invoke(this,fromClient,channel,arg,id);
                        break;
                }
                
                if (reply!=null)
                    send(fromClient,channel,reply,id);
            }
            catch (Exception e)
            {
                exception(fromClient,toClient,msg,e);
            }
            catch (Error e)
            {
                exception(fromClient,toClient,msg,e);
            }
        }
    }

    /* ------------------------------------------------------------ */
    /* ------------------------------------------------------------ */
    private class Listen implements MessageListener
    {
        public void deliver(Client fromClient, Client toClient, Message msg)
        {
            BayeuxService.this.deliver(fromClient,toClient,msg);
        }
    }

}

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