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ActiveMQ example source code file (amq.js)

This example ActiveMQ source code file (amq.js) 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.

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The ActiveMQ amq.js source code

/**
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

// AMQ Ajax handler
// This class provides the main API for using the Ajax features of AMQ. It
// allows JMS messages to be sent and received from javascript when used
// with the org.apache.activemq.web.MessageListenerServlet.
//
// This version of the file provides an adapter interface for the jquery library
// and a namespace for the Javascript file, private/public variables and
// methods, and other scripting niceties. -- jim cook 2007/08/28

var org = org || {};
org.activemq = org.activemq || {};

org.activemq.Amq = function() {
	var connectStatusHandler;

	// Just a shortcut to eliminate some redundant typing.
	var adapter = org.activemq.AmqAdapter;

	if (typeof adapter == 'undefined') {
		throw 'An org.activemq.AmqAdapter must be declared before the amq.js script file.'
	}

	// The URI of the AjaxServlet.
	var uri;

	// The number of seconds that the long-polling socket will stay connected.
	// Best to keep this to a value less than one minute.
	var timeout;

	// A session should not be considered initialized until the JSESSIONID is returned
	// from the initial GET request.  Otherwise subscription POSTS may register the
	// subscription with the wrong session.
	var sessionInitialized = false;

	// This callback will be called after the first GET request returns.
	var sessionInitializedCallback;	

	// Poll delay. if set to positive integer, this is the time to wait in ms
	// before sending the next poll after the last completes.
	var pollDelay;

	// Inidicates whether logging is active or not. Not by default.
	var logging = false;

	// 5 second delay if an error occurs during poll. This could be due to
	// server capacity problems or a timeout condition.
	var pollErrorDelay = 5000;

	// Map of handlers that will respond to message receipts. The id used during
	// addListener(id, destination, handler) is used to key the callback
	// handler.  
	var messageHandlers = {};

	// Indicates whether an AJAX post call is in progress.
	var batchInProgress = false;

	// A collection of pending messages that accumulate when an AJAX call is in
	// progress. These messages will be delivered as soon as the current call
	// completes. The array contains objects in the format { destination,
	// message, messageType }.
	var messageQueue = [];

  // String to distinguish this client from others sharing the same session.
  // This can occur when multiple browser windows or tabs using amq.js simultaneously.
  // All windows share the same JESSIONID, but need to consume messages independently.
  var clientId = null;
  
	/**
	 * Iterate over the returned XML and for each message in the response, 
	 * invoke the handler with the matching id.
	 */
	var messageHandler = function(data) {
		var response = data.getElementsByTagName("ajax-response");
		if (response != null && response.length == 1) {
			connectStatusHandler(true);
			var responses = response[0].childNodes;    // <response>
			for (var i = 0; i < responses.length; i++) {
				var responseElement = responses[i];

				// only process nodes of type element.....
				if (responseElement.nodeType != 1) continue;

				var id = responseElement.getAttribute('id');

				var handler = messageHandlers[id];

				if (logging && handler == null) {
					adapter.log('No handler found to match message with id = ' + id);
					continue;
				}

				// Loop thru and handle each <message>
				for (var j = 0; j < responseElement.childNodes.length; j++) {
					handler(responseElement.childNodes[j]);
				}
			}
		}
	};

	var errorHandler = function(xhr, status, ex) {
		connectStatusHandler(false);
		if (logging) adapter.log('Error occurred in ajax call. HTTP result: ' +
		                         xhr.status + ', status: ' + status);
	}

	var pollErrorHandler = function(xhr, status, ex) {
		connectStatusHandler(false);
		if (status === 'error' && xhr.status === 0) {
			if (logging) adapter.log('Server connection dropped.');
			setTimeout(function() { sendPoll(); }, pollErrorDelay);
			return;
		}
		if (logging) adapter.log('Error occurred in poll. HTTP result: ' +
		                         xhr.status + ', status: ' + status);
		setTimeout(function() { sendPoll(); }, pollErrorDelay);
	}

	var pollHandler = function(data) {
		try {
			messageHandler(data);
		} catch(e) {
			if (logging) adapter.log('Exception in the poll handler: ' + data, e);
			throw(e);
		} finally {
			setTimeout(sendPoll, pollDelay);
		}
	};

	var initHandler = function(data) {
		sessionInitialized = true;
		if(sessionInitializedCallback) {
			sessionInitializedCallback();
		}
		sendPoll();
	}

	var sendPoll = function() {
		// Workaround IE6 bug where it caches the response
		// Generate a unique query string with date and random
		var now = new Date();
		var timeoutArg = sessionInitialized ? timeout : 0.001;
		var data = 'timeout=' + timeoutArg * 1000
				 + '&d=' + now.getTime()
				 + '&r=' + Math.random();
		var successCallback = sessionInitialized ? pollHandler : initHandler;

		var options = { method: 'get',
			data: addClientId( data ),
			success: successCallback,
			error: pollErrorHandler};
		adapter.ajax(uri, options);
	};

	var sendJmsMessage = function(destination, message, type, headers) {
		var message = {
			destination: destination,
			message: message,
			messageType: type
		};
		// Add message to outbound queue
		if (batchInProgress) {
			messageQueue[messageQueue.length] = {message:message, headers:headers};
		} else {
			org.activemq.Amq.startBatch();
			adapter.ajax(uri, { method: 'post',
				data: addClientId( buildParams( [message] ) ),
				error: errorHandler,
				headers: headers,
				success: org.activemq.Amq.endBatch});
		}
	};

	var buildParams = function(msgs) {
		var s = [];
		for (var i = 0, c = msgs.length; i < c; i++) {
			if (i != 0) s[s.length] = '&';
			s[s.length] = ((i == 0) ? 'destination' : 'd' + i);
			s[s.length] = '=';
			s[s.length] = msgs[i].destination;
			s[s.length] = ((i == 0) ? '&message' : '&m' + i);
			s[s.length] = '=';
			s[s.length] = msgs[i].message;
			s[s.length] = ((i == 0) ? '&type' : '&t' + i);
			s[s.length] = '=';
			s[s.length] = msgs[i].messageType;
		}
		return s.join('');
	}
	
	// add clientId to data if it exists, before passing data to ajax connection adapter.
	var addClientId = function( data ) {
		var output = data || '';
		if( clientId ) {
			if( output.length > 0 ) {
				output += '&';
			}
			output += 'clientId='+clientId;
		}
		return output;
	}

	return {
		// optional clientId can be supplied to allow multiple clients (browser windows) within the same session.
		init : function(options) {
			connectStatusHandler = options.connectStatusHandler || function(connected){};
			uri = options.uri || '/amq';
			pollDelay = typeof options.pollDelay == 'number' ? options.pollDelay : 0;
			timeout = typeof options.timeout == 'number' ? options.timeout : 25;
			logging = options.logging;
			sessionInitializedCallback = options.sessionInitializedCallback
			clientId = options.clientId;
			adapter.init(options);
			sendPoll();
			
		},
		    
		startBatch : function() {
			batchInProgress = true;
		},

		endBatch : function() {
			if (messageQueue.length > 0) {
				var messagesToSend = [];
				var messagesToQueue = [];
				var outgoingHeaders = null;
				
				// we need to ensure that messages which set headers are sent by themselves.
				// if 2 'listen' messages were sent together, and a 'selector' header were added to one of them,
				// AMQ would add the selector to both 'listen' commands.
				for(i=0;i<messageQueue.length;i++) {
					// a message with headers should always be sent by itself.	if other messages have been added, send this one later.
					if ( messageQueue[ i ].headers && messagesToSend.length == 0 ) {
						messagesToSend[ messagesToSend.length ] = messageQueue[ i ].message;
						outgoingHeaders = messageQueue[ i ].headers;
					} else if ( ! messageQueue[ i ].headers && ! outgoingHeaders ) {
						messagesToSend[ messagesToSend.length ] = messageQueue[ i ].message;
					} else {
						messagesToQueue[ messagesToQueue.length ] = messageQueue[ i ];
					}
				}
				var body = buildParams(messagesToSend);
				messageQueue = messagesToQueue;
				org.activemq.Amq.startBatch();
				adapter.ajax(uri, {
					method: 'post',
					headers: outgoingHeaders,
					data: addClientId( body ),
					success: org.activemq.Amq.endBatch, 
					error: errorHandler});
			} else {
				batchInProgress = false;
			}
		},

		// Send a JMS message to a destination (eg topic://MY.TOPIC).  Message
		// should be xml or encoded xml content.
		sendMessage : function(destination, message) {
			sendJmsMessage(destination, message, 'send');
		},

		// Listen on a channel or topic.
		// handler must be a function taking a message argument
		//
		// Supported options:
		//  selector: If supplied, it should be a SQL92 string like "property-name='value'"
		//            http://activemq.apache.org/selectors.html
		//
		// Example: addListener( 'handler', 'topic://test-topic', function(msg) { return msg; }, { selector: "property-name='property-value'" } )
		addListener : function(id, destination, handler, options) {
			messageHandlers[id] = handler;
			var headers = options && options.selector ? {selector:options.selector} : null;
			sendJmsMessage(destination, id, 'listen', headers);
		},

		// remove Listener from channel or topic.
		removeListener : function(id, destination) {
			messageHandlers[id] = null;
			sendJmsMessage(destination, id, 'unlisten');
		},
		
		// for unit testing
		getMessageQueue: function() {
			return messageQueue;
		},
		testPollHandler: function( data ) {
			return pollHandler( data );
		}
	};
}();

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