Friday, December 31, 2010

Remote Observer Pattern with Publish-Subcribe via XMPP [Apache Camel Series]

Apache Camel is a powerful message routing framework that can be used to implement all common enterprise integration patterns.

I'm going to look at Remote Observer Pattern, which is understandable complex to implement using traditional techniques.

However, with Apache Camel, it becomes surprisingly simple!

Reviewing the API

I'll just expand upon the previously blogged Asynchronous Observer/Listener with Apache Camel.

Here's the Listener interface, which is still the same:

public interface InvoiceListener {
public void invoiceCreated(int id, String name);

Still the same exact old Listener API, to prove that Apache Camel can be unobtrusive if you want. (yes, I want it to "stay out of my API way". Let Camel be the glue.)

And the same way to call the Observer :

invoiceListener.invoiceCreated(243, "Sumba Enterprise");

Publish-Subscribe Pattern via XMPP

What I want to do is route the listener invocation from the caller through a message queue channel/topic.

Interested observers can subscribe to that topic to receive (aka "consume" in Camel-speak) events/notifications/messages.

This is called Publish-Subscribe in Enterprise Integration Patterns.
The usual way to do this would be to use JMS and a message queue server/broker such as Apache ActiveMQ.

But it doesn't have to be. Besides if you use JMS directly you'll be tied to JMS API.

With Apache Camel you're free to change the underlying routing as you wish (XMPP, JMS, direct call, etc.).

Even if you want to change to another routing framework e.g. Spring Integration it's possible since both framework support the POJO bean proxying approach.

I have at least four reasons to use XMPP:
  1. It's very easy to debug. When there are problems you can just use Pidgin or Empathy or Spark or any XMPP/Jabber client to monitor what flows inside the pipes. No need for heavy tools. Even your grandma's mobile phone can do the job.
  2. No tooling needed. Same as above. JMS/ActiveMQ may have more/better tooling but you need the tooling. This can be either strength or weakness depending on how you look at it.
  3. It's just HTTP. I have never tried it but theoretically you can use any HTTP tool to tweak inside XMPP packets since in a way it's "XML over HTTP".
  4. No fancy server needed. You can install Openfire or ejabberd, just like you can install ActiveMQ. But you don't have to, you can use Jabber network or Google Talk or Google Apps' GTalk or even Facebook Chat's XMPP support. All free to use. (If you decide to use these services make sure to comply to their terms of use.)
Note: XMPP server/network's support of XMPP conference room chat functionality may vary.

Adding Camel XMPP and JSON Serialization

To use Camel with XMPP, let's revisit our project's Gradle build script and add camel-xmpp and camel-xstream as dependencies :

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'maven'
sourceCompatibility = '1.6'
repositories {
mavenRepo urls: "file:${['user.home']}/.m2/repository", name: 'local'
dependencies {
compile 'org.slf4j:slf4j-api:1.6.1'
runtime 'org.slf4j:jcl-over-slf4j:1.6.1'
runtime 'ch.qos.logback:logback-classic:0.9.26'
compile 'org.apache.camel:camel-core:2.5.0'
runtime 'org.apache.camel:camel-xmpp:2.5.0'
runtime 'org.apache.camel:camel-xstream:2.5.0'

While it's possible to use just Camel XMPP without Xstream, in practice it's much easier if we use a serialization library.

Camel provides several providers to serialize (i.e. marshall and unmarshall) our invocation/messages over the network transport (such as XMPP).
Camel calls these providers Data Formats.

I like to use JSON because it's somewhat human-readable (at least it's programmer-readable! :-) ) and relatively compact.

XML is also okay if you prefer it, both are supported by Xstream.

Camel also supports another JSON provider called Jackson but I wasn't able to successfully marshal BeanInvocation (Camel's underlying data class for proxied bean invocation) with it, so it's Xstream for now.

Routing to XMPP

 Let's review the last routing we had :


This is fine. To make our invocation support XMPP all we need to do is change the routes, nothing else:

final String xmppUri = "xmpp://abispulsabot@localhost/?room=abispulsa.refill&password=test";

This is all that's needed. Apart from adding the dependencies that we've done above, no code needs to be changed!

I'm sure you can guess what the URI means, it tells Camel XMPP connector to create an XMPP endpoint with:
  • username: abispulsabot
  • domain: localhost
  • room: abispulsa.refill
  • password: test
I guess I didn't really have to write that, but just for the sake of assertiveness. ;-)

Note: if you want to use XML just change un/marshal().json() to un/marshal().xstream(). Simple isn't it? No fuss. ;-)

Making It Behave

The above routing is still not cool:
  1. It's single-threaded, i.e. both incoming and outgoing messages are blocking.
  2. It does not handle non-JSON messages.
So let's make it better.

Enabling Multi-threading aka Asynchronous Processing

To enable multi-threading we use the magic threads() DSL :

final String xmppUri = "xmpp://abispulsabot@localhost/?room=abispulsa.refill&password=test";

That's it. Now each processing will use its own thread (up to a default maximum of 10 threads per thread pool, but you can configure, e.g. "threads(5)")

Logging Non-JSON Messages

So what happens when a non-JSON messages is posted to the XMPP room? Let's just log it:

final String xmppUri = "xmpp://abispulsabot@localhost/?room=abispulsa.refill&password=test";

We use conditional routing there, using choice() and  when() and otherwise().
And Predicates (constraint expressions) such as body().startsWith().
By the way, Camel supports Predicates with a lot more expression languages, so you won't run out of options.

You'll complain that the above routing still doesn't handle invalid JSON, but let's just be satisfied with that as my example.
I believe you can make better routes much faster than I do. ;-)

And So It Goes...

Again for the sake of completeness, I present you the entire app:

import org.apache.camel.CamelContext;
import org.apache.camel.builder.ProxyBuilder;
import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.impl.DefaultCamelContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
private static Logger logger = LoggerFactory.getLogger(App.class);
private static LoggerInvoiceListener loggerInvoiceListener = new LoggerInvoiceListener();
private static InvoiceListener invoiceListener;
CamelContext camelContext = new DefaultCamelContext();
loggerInvoiceListener = new LoggerInvoiceListener();
final String xmppUri = "xmpp://abispulsabot@localhost/?room=abispulsa.refill&password=test";
camelContext.addRoutes(new RouteBuilder() {
public void configure() throws Exception {
invoiceListener = new ProxyBuilder(camelContext).endpoint("direct:invoice").build(InvoiceListener.class);
invoiceListener.invoiceCreated(243, "Sumba Enterprise");"first invoice sent");
invoiceListener.invoiceCreated(938, "Mina Co.");"second invoice sent");
invoiceListener.invoiceCreated(312, "Crux Market");"third invoice sent");
try {
while (true) { // event loop so you can send messages
} finally {

Here's an example log output:

00:57:03.280 [main] INFO  o.a.c.c.xmpp.XmppGroupChatProducer - Joined room: abispulsa.refill@conference.annafi as: abispulsabot
00:57:03.298 [main] INFO  o.a.camel.impl.DefaultCamelContext - Route: route1 started and consuming from: Endpoint[direct://invoice]
00:57:03.338 [main] INFO  o.a.c.component.xmpp.XmppConsumer - Joined room: abispulsa.refill@conference.annafi as: abispulsabot
00:57:03.338 [main] INFO  o.a.camel.impl.DefaultCamelContext - Route: route2 started and consuming from: Endpoint[xmpp://abispulsabot@localhost/?password=******&room=abispulsa.refill]
00:57:03.339 [main] INFO  o.a.camel.impl.DefaultCamelContext - Total 2 routes, of which 2 is started.
00:57:03.339 [main] INFO  o.a.camel.impl.DefaultCamelContext - Apache Camel 2.5.0 (CamelContext: camel-1) started in 16.448 seconds
00:57:03.510 [main] INFO - first invoice sent
00:57:03.528 [main] INFO - second invoice sent
00:57:03.557 [main] INFO - third invoice sent
00:57:03.570 [Camel Thread 2 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - Invoice #243 name: Sumba Enterprise created
00:57:05.071 [Camel Thread 2 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - 243/Sumba Enterprise done!
00:57:05.078 [Camel Thread 4 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - Invoice #938 name: Mina Co. created
00:57:06.579 [Camel Thread 4 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - 938/Mina Co. done!
00:57:06.584 [Camel Thread 5 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - Invoice #312 name: Crux Market created
00:57:08.085 [Camel Thread 5 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - 312/Crux Market done!
00:57:26.399 [Camel Thread 6 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - Invoice #7890 name: Bippo Indonesia created
00:57:27.900 [Camel Thread 6 - Threads] INFO  i.c.b.c.LoggerInvoiceListener - 7890/Bippo Indonesia done!
00:57:41.776 [Camel Thread 7 - Threads] INFO  xmpp - Exchange[ExchangePattern:InOnly, BodyType:String, Body:You can also filter messages! :)]

Notice that in the above log I posted an invoice #7890 "Bippo Indonesia" using Pidgin XMPP client, and the application can process it successfully.
I also said "You can also filter messages! :)" that simply gets logged.

As a cool bonus I provide a screenshot. ;-)

Extra: Gradle JavaExec

To quickly run the application from the command line, Gradle provides a JavaExec task that can be used like this in build.gradle :

task(exec, dependsOn: classes, type: JavaExec) {
description = 'Run the application'
classpath = runtimeClasspath
main = ''

Extra: logback.xml Configuration File

Logback defaults to logging everything to stdout (which is much better than Log4j's default of not logging anything!)

I prefer logging only INFO level, this can be done by putting the following logback.xml in src/main/resources :

  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <layout class="ch.qos.logback.classic.PatternLayout">
      <Pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</Pattern>
  <root level="info">
    <appender-ref ref="STDOUT" />

Utopian dream: I can't help but imagine that had Logback used Gradle-style configuration it would look like this: ;-)

appenders { stdConsole() }
root.level = info

Running the Example

To make it really easy for you (especially to myself, as I tend to forget things!), I've made the examples freely available as camel-xmpp-redo project on GitHub.

You'll need Git and Gradle to checkout then build it (and JDK 1.6).
Gradle will automatically download and cache the required dependencies for you.

git clone git://
cd camel-xmpp-redo
# edit the source and change XMPP credentials
gradle exec
Note: you must change the XMPP credentials used to login.

Easy XMPP with Camel !

Apache Camel is unobtrusive way to add flexibility of routing, messaging, and integration patterns with XMPP or other connectors supported by Camel.
(you can create your own connectors if you want...)

I highly suggest the Camel in Action Book for the best in-depth guide and examples for using Camel to develop your applications more productively.


Claus Ibsen said...

Nice blog entry. I added a link to it from the Camel articles page

Hendy Irawan said...

@Claus Thank you! I feel honored.

I hope you don't mind if I also request the other article to be there too :


Claus Ibsen said...

Yes I have added that 2nd article as well. Keep 'em coming :)

Hendy Irawan said...

@Claus thank youu :)

Anonymous said...

Thank you for posting such a great article! I found your website perfect for my needs. It contains wonderful and helpful posts. Keep up the good work! | | | | | | | | | |

coach factore outlet said...

Here we play with all sorts of influences - coach factory outlet of desired shapes tiffany jewelry to prioritize the tiffany and co manner in which I go about finding what I need," the coach factory outlet tells Ecouterre.More than 1,000 runners began the race.Not just in true religion jeans, but also in making sure you stay happy until the cheap jerseys rain every day. Hey, $350 is way less than those coach outlet. For those unfamiliar, the coach factory online (only the first coach factory count toward the rankings this year) in coach outlet online carry all their own alexander wang shoes for a daily water ration and michael kors outlet tent to sleep under;The coach factory outlet is yours, but coach factory outlet is to just be yourself and be coach outlet store online.The sleek ensemble came on show through sac burberry. Choose from brands like Bernardo, michael kors outlet and others.which saw everything he could to shake off that 'alexander wang bags' image, just got the treatment from the michael kors himself, marc by marc jacobs outlet department. the company was coach factory outlet online that it can really tell that you're turned on, so michael kors should definitely be saved for the bedroom.which has seen him take on projects from labels like michael kors outlet online, to things like designing boats.

Anonymous said...

Keep sharing such ideas in the future as well. This was actually what I was looking for, and I am glad to came here! Thanks for sharing the such information with | | | | | | | | | |

polo outlet said... Burberry Outlet Air Max Shoes Coach Black Friday Coach Black Friday Coach Cyber Monday Coach Factory Coach Outlet Factory Coach Outlet USA Coach Purses Factory Coach Purses USA Coach Store Outlet Coach Purses On Sale Monster Beats Outlet Louis Vuitton Outlet Louis Vuitton Factory Marc Jacobs On Sale MCM Outlet MCM 店铺 cheap oakley sunglasses Michael Kors Outlet Michael Kors Outlet Michael Kors Factory Michael Kors Outlet Michael Kors Factory Online Coach Factory Outlet North Face Outlet Online Polo Outlet Store Ralph Lauren UK Sac Longchamp Pairs Coach Outlet Online Coach Factory Oultet Barbour Jackets Outlet Online Canada Goose Outlet Gucci Outlet Online Michael Kors Outlet Moncler Clearance Moncler Jackets Outlet Online North Clearace Outlet Polo Ralph Lauren Outlet Online Woolrich Clearance Michael Kors Factory Outlet Coach Outlet Online USA Beats by Dre Coach Purses Outlet Online Michael Kors USA

Eric Simmons said...

Great and Useful Article.

Online Java Course

Java Online Training

Java Course Online

J2EE training

online J2EE training

Best Recommended books for Spring framework

Java Interview Questions

Java Training Institutes in Chennai

Java Training in Chennai

J2EE Training in Chennai

java j2ee training institutes in chennai

Java Course in Chennai

oakleyses said...

burberry handbags, prada outlet, ray ban sunglasses, gucci handbags, tiffany and co, louis vuitton, christian louboutin outlet, christian louboutin uk, tory burch outlet, ray ban sunglasses, polo ralph lauren outlet online, louis vuitton outlet, jordan shoes, michael kors outlet online, nike air max, christian louboutin, ray ban sunglasses, louis vuitton outlet, longchamp outlet, prada handbags, michael kors outlet online, uggs outlet, christian louboutin shoes, uggs on sale, ugg boots, louis vuitton outlet, chanel handbags, longchamp outlet, oakley sunglasses, nike outlet, louis vuitton, uggs outlet, polo outlet, michael kors outlet, burberry outlet, tiffany jewelry, michael kors outlet online, oakley sunglasses, nike air max, ugg boots, michael kors outlet online, oakley sunglasses, replica watches, nike free, michael kors outlet, replica watches, longchamp outlet, kate spade outlet

oakleyses said...

sac vanessa bruno, hollister uk, polo lacoste, vans pas cher, nike roshe run uk, nike free uk, true religion outlet, air max, polo ralph lauren, coach purses, louboutin pas cher, hollister pas cher, kate spade, lululemon canada, timberland pas cher, michael kors outlet, sac longchamp pas cher, michael kors pas cher, ray ban pas cher, true religion outlet, abercrombie and fitch uk, nike air max uk, replica handbags, nike air max uk, nike blazer pas cher, coach outlet, nike roshe, michael kors, mulberry uk, coach outlet store online, burberry pas cher, guess pas cher, nike air max, sac hermes, michael kors, north face uk, hogan outlet, north face, converse pas cher, oakley pas cher, ralph lauren uk, true religion outlet, new balance, jordan pas cher, nike free run, nike tn, longchamp pas cher, true religion jeans, nike air force, ray ban uk

oakleyses said...

hollister, north face outlet, mac cosmetics, baseball bats, nike huaraches, babyliss, new balance shoes, iphone cases, chi flat iron, louboutin, ferragamo shoes, iphone 5s cases, longchamp uk, soccer shoes, mcm handbags, nike roshe run, timberland boots, mont blanc pens, vans outlet, bottega veneta, instyler, oakley, ralph lauren, valentino shoes, giuseppe zanotti outlet, s6 case, p90x workout, celine handbags, iphone 6s plus cases, herve leger, north face outlet, nike trainers uk, ipad cases, iphone 6s cases, lululemon, wedding dresses, nike air max, abercrombie and fitch, nfl jerseys, hermes belt, insanity workout, ghd hair, asics running shoes, beats by dre, iphone 6 cases, reebok outlet, jimmy choo outlet, soccer jerseys, hollister clothing, iphone 6 plus cases

oakleyses said...

pandora jewelry, canada goose uk, canada goose, barbour, moncler, karen millen uk, swarovski crystal, replica watches, louis vuitton, canada goose, louis vuitton, juicy couture outlet, nike air max, lancel, swarovski, canada goose jackets, gucci, converse, thomas sabo, canada goose outlet, pandora charms, ugg,uggs,uggs canada, juicy couture outlet, doudoune moncler, hollister, moncler, montre pas cher, coach outlet, links of london, hollister, ugg uk, ugg, toms shoes, marc jacobs, pandora uk, vans, canada goose, moncler, canada goose outlet, moncler outlet, moncler outlet, louis vuitton, moncler, ray ban, louis vuitton, louis vuitton, converse outlet, moncler uk, ugg,ugg australia,ugg italia, supra shoes, barbour uk

Getit said...

This post is superb

Zapya for PC
Zapya free download
Zapya download
Zapya apk

Nithyanantham M said...

Thanks for sharing this post
Dailymotion video downloader

Try Dailymotion video
to download videos from dailymotion.

Nithyanantham M said...

Thanks for sharing this post
Dailymotion video downloader

Try Dailymotion video
to download videos from dailymotion.

Post a Comment

Copyright 2009 Spring vs Java EE Web Dev. Powered by Blogger Blogger Templates create by Deluxe Templates. WP by Masterplan