A simple content-based router

The problem I was trying to solve was that a legacy application was designed to listen to a WebSphere MQ queue, which would contain requests for a variety of operations. A new application had been developed to handle a subset of these operations. I couldn’t have both applications listening to the same queue, so I needed to divert particular operation request messages to a separate new queue.

I needed to put together a simple content-based router that would inspect the header of each incoming message and route the message to a different destination depending on the operation name. I was able to implement this by defining a route which used XPath to select an endpoint based on XML attributes. This could be done in the Camel context XML file and the project contained no code outside this file.


<camelContext xmlns="http://camel.apache.org/schema/spring">
<route>
<from uri="webspheremq:ANY.OPERATION.REQUEST" />
<choice>
<when>
<xpath>/REQUEST/HEADER[@OperationName='Old.Request']</xpath>
<to uri="activemq:OLD.REQUEST"/>
</when>
<when>
<xpath>/REQUEST/HEADER[@OperationName='New.Request']</xpath>
<to uri="activemq:NEW.REQUEST"/>
</when>
<otherwise>
<to uri="activemq:DEAD.LETTER.QUEUE"/>
</otherwise>
</choice>
</route>
</camelContext>


A CSV to XML transform

Here, I was dealing with integrating two off the shelf applications, the aim being to facilitating exporting a document and meta data from one system and importing it into the other. When exporting a document from the first application, a CSV would be generated in a directory on the filesystem. The other application provided an import adapter, which required an XML trigger file. I needed a small application to follow the following steps:

1. Listen for CSV files being dropped in a directory on the filesystem.
2. Split the CSV up into separate requests for each document being exported.
3. Generate an XML trigger file for each request.
4. Drop the XML trigger file into a directory ready for import by the downstream system.

As well as providing middleware messaging adapters, Camel also supports defining endpoints that are directories on the filesystem, so it can automatically create a listener for a directory. To deal with the first two steps, I made use of opencsv to parse the CSV, but as I soon discovered, Camel also provided CSV unmarshallers.

I extended the Camel RouteBuilder and using the fluent DSL for Java, defined my routes and created a Splitter class that would take the unmarshalled CSV and output a list of messages (List<List<List<String>>>) to an internal queue., this looked a bit like the following:

from("C:/router/export/csv/")
.unmarshal().csv()
.split().method("org.gratiartis.router.Splitter", "split")
.to("jms:DOCUMENT.METADATA.QUEUE");

I then defined a route to pick the individual metadata messages off the internal queue and use a Processor to generate XML in the required format.

from("jms:DOCUMENT.METADATA.QUEUE")
.processRef("org.gratiartis.router.Processor")
.to("C:/router/out/xml/");

Further reading

Camel is very comprehensive and is also one of the best documented projects out there. I keep trying to implement something myself and then finding that there’s already something that will do the job for me.

These are probably the best starting points for info on any particular integration pattern:

http://camel.apache.org/enterprise-integration-patterns.html
http://camel.apache.org/architecture.html

And this was one of the better tutorial introductions to it:

http://architects.dzone.com/articles/apache-camel-integration

If Camel sounds good, you should also take a look at Spring Integration. It’s another framework based on the patterns in the Enterprise Integration Patterns book, but has that Spring tendency towards implementation through bean annotations. But you don’t have to pick one or the other; the Camel project has developed the camel-spring-integration library to provide a bridge from Camel components to Spring Integration endpoints: http://camel.apache.org/springintegration.html

As far as I an tell, there is very little first hand information available online for anyone thinking of moving out there. I’m thinking I might try to relate some of my experiences of the process of becoming an ex-pat, in the hope that others might find my mistakes and successes educational or just plain amusing.

I have been playing with a few today, and I think I have found one that works just how I want it to. My personal winner is the Flickr Gallery plugin for WordPress. You can also check out the Flickr Gallery project web site for more detail.

All you need to do is install it, request a Flickr API key (these cost nothing for personal or small business use) and put it in your configuration. Then whenever you want a post to show a Flickr photo set as a gallery, you just put in a tag like this:
[flickr-gallery mode="photoset" photoset="72157625782372674"]
… to see this:

It’s not limited to photo sets. You can show specific photos, your photostream, galleries based on tags and more.

And in case you were wondering, I have no connection to the developer of this plugin. I just feel that such a handy plugin merits any publicity I can give it.

Coincidentally, I also upgraded to Aperture 3 this morning, which enables me to upload a group of photos to a Flickr set in about 2 clicks. Managing photos and publishing them online is starting to feel frictionless.

Pete Tibbitts used to work with me when our Halifax Treasury team was very small. I think it was just Pete, Glenn and myself working as developers at the time. Pete was a young-un, so obviously he moved on after a while and took up a career as an IBM consultant. That mostly seemed to involve developing apps for the DVLA in Swansea. Well, he decided that it would be nice to take a break from the rat race, so he blagged himself a career break from IBM and has headed off to spend a year traveling around South America. He’s currently in Columbia, blogging about the people he meets and learning Spanish. I must admit I’m a bit envious!

If you’re thinking of heading out in the direction of Portugal (particularly the Silver Coast), please take a look at the web site. Hopefully you can find a nice place to stay. If you’re thinking of buying your own property in the area, why not drop him a note? He knows the area well and is friendly with a few estate agents, so he might be able to provide some useful guidance.

Now I just need to get myself out there and find out for myself whether Sao Martinho do Porto is as nice as everyone says it is!

Rio de Janeiro Maru

Nippo Maru

Sankisan Maru

Kensho Maru

Yamagiri Maru

Submarine I-169 “Shinohara”

Heian Maru

Kiyosumi Maru

Fujikawa Maru

Java Development

Eclipse (http://www.eclipse.org/)

Still my favourite IDE for Java development with a whole host of useful plug-ins.

NetBeans (http://www.netbeans.org/)

A decent IDE for Java development, but not up there with Eclipse yet. Version 6 is good though if you’re happy to pick up the development builds. Once that’s complete t will be a real challenger.

Maven (http://maven.apache.org/)

You want to make sure your builds work no matter what platform you’re on? This is a very good way of making sure that happens.

BEA WebLogic

I’m generally a Java EE developer, and the platform that I target at work is WebLogic. Take a look at my WebLogic on Mac OS X page for more information about how to get the server running on OS X.

TeX Development

I do quite a bit of writing using LaTeX for my typesetting. You’ll find a few examples on this site where I have used it to generate PDFs. In the past I have worked on Windows with TeXnicCenter which made working with a large project easy and I used the MikTeX distribution which contains the useful utilities that allowed me to script generating the work products. But what do I do now that I’m trying to do everything on the Mac? As you might expect with something as well established as LaTeX, there is plenty of software that can be used on all sorts of platforms.

MacTex (http://www.tug.org/mactex/)

MacTeX is a collection of front-ends, documentation and utilities for TeX development. I should warn you that it’s over 700MB, so it will take some time to download!