Eclipse, Tomcat, Sysdeo and the DevLoader (and a little Maven)

If you are developing a webapp in Eclipse there is a very good chance you are using Sysdeo. If you are not there is a very good chance you have not yet learned a proper way to debug a Java web application (or maybe you are using Jetty?). Sysdeo is really the only good open source, free Eclipse plugin for developing with Tomcat. It allows a simple way to debug your code in Eclipse while it runs in Tomkitty, a very nice thing.

Now the problem with the plugin out right is your project must be laid out like an exploded war... YUCK! This is because Sysdeo will be looking for the lib files under WEB-INF/lib and such. Often I've seen this lead to some truly horrible project organization, where jsp and Ant build files co-mingle in the same folder!?!

Most of us use a sane Ant or Maven project layout that is standardized across all our Java projects. If you want to continue doing so and leverage the benefits of Sysdeo then you will need the DevLoader installed.

If you haven't downloaded and installed the Sysdeo plugin do so now, I will wait ;)

Go here to get Sysdeo!

Ok once installed you should see 3 icons under the Eclipse menu bar that look very familiar (they are Tomcats!). The first icon starts Tomcat, the second stops it and the third restarts. Now open the Eclipse preferences menu. You should see the "Tomcat" entry. Open it and configure the plugin based on your Tomcat installation. You will want the "Context Declaration mode" to be "context" in my experience. It just makes things a lot cleaner if you use Tomcat for other projects/apps, where they each have individual files rather being crammed in server.xml. That should be about all you need to know. Oh the sub-menu 'Source path' is for adding the source files used in debugging, so make sure your project is in there if you want to be able to see the files while debugging.

Next up the DevLoader. It came with the Sysdeo plugin when you download it! You should find a zip file in the the Sysdeo zip aptly named Devloader.zip. Unzip it. It will create an org folder, within lies some classes. Jar this sucker up:

   jar cf devloader.jar org/

This should create a jar for the DevLoader. Now throw this in your Tomcat instance's lib folder.

Great now you have almost everything you need to get started. Lets go over an example of a Maven project being used.

In Maven the webapp files go in src/main/webapp by convention, and sources go in src/main/java, and the resource files (xml, properties) go into src/main/resources. For your Maven project you would right click the project and select properties. You should now notice a 'Tomcat' entry in the config options. Select this.

Enable the "Is a Tomcat Project" checkbox. For the 'context name' use whatever sane value you prefer. Near the bottom area you will want to enter 'src/main/webapp' for the app root. This is where most jsp, html, javascrpt, css and whatnot will be. You will be able to update these and see the result. Now the last thing we need to do is activate the devloader. Here is a picture of what that looks like:

So really all you do is add the jar files needed. Thats it. Now save. If you are not going to create a context file yourself, and you enabled 'can update context definition' in the projects tomcat properties you can right click the project and select "tomcat project > update context definition". This will automatically create the proper context file for Tomcat, so that it uses the DevLoader and your project. You almost certainly will want to do this. Note you can further alter the automatically created context file afterwards.

Sorting using Haskell

Last Friday night I had some fun writing sorts in Haskell. Yes thats right I spent my Friday night working on some rudimentary algorithms in an obscure computer language. Lets just say I'm in to that kinda thing. Oh well it beats being addicted to cough syrup.

So Haskell is fun. There I said it. It is the kinda language which lends much balance to ones style, is one is a imperitive/OO language flunky. The ideas in Haskell seem bizarre at first but become beautiful as they sink in. Sink they do, lets look at the first sort, the almighty BUBBLE SORT

-- Implementation of a bubble sort in Haskell
bubbleSort :: (Ord t) => [t] -> [t] -- signature
bubbleSort a = loop (length a) bubble a

bubble :: (Ord t) => [t] -> [t] 
bubble (a:b:c) | a < b = a : bubble (b:c)
               | otherwise = b : bubble (a:c)
bubble (a:[]) = [a] 
bubble [] = []

loop :: (Num a, Ord a) => a -> (t -> t) -> t -> t
loop num f x | num > 0 =  loop (num-1) f x'
             | otherwise = x
             where x' = f x

I imagine that looks weird. Well it should, if you are unaccustomed to Haskell. The syntax is much different than any OO language. I've had people tell me Python is too weird looking. Well this would just frighten those types of people silly. Lets talk about this code

The first thing to point out is the signature. In leyman's terms this says "take a list of something and return a list of something". The last [t] is going to be what is returned. The '(Ord t)' says that t must be of the typeclass 'Ord' as in 'Ordinality' which is related to being able to compare values. Don't worry too much about that for now, just know it allows us to do things like '>', '<', '==' and so on.

The rest is easy to explain. The bubbleSort function will loop x times, x being the length of the list to be sorted. For a list of 10 elements we loop 10 times. Each time we loop we call bubble. See the loop function takes a number (a) and a function (t -> t), and finally a value (t). What we end up doing here is calling loop again with the number decremented by one. We call bubble on the value, then passing the result right back into bubble IF the number is greater than 0.

This bubble function will go through the list comparing each pair elements, starting with the first and second, and swapping them if the first is greater than the second. This causes the largest value to 'bubble up' to the top of the list.

Languages

This is a quick post about some great learning options for a pair of functional languages. You may be interested in seeing a functional approach to computer languages. I recommend Haskell or Erlang. For Haskell I recommend the book "Real World Haskell". You can read it online; it will also be published by O'Reilly. For Erlang check out "Getting Started with Erlang", also free. Once you've wet your feet with Erlang you can check read the manual whenever you need a refresher.

Hacking Eclipse plugin configurations

Reading Neal Ford's generally excellent book The Productive Programmer, I experimented with his multiple plugin configuration hack. In short, creating multiple plugin configurations in a single eclipse install allows for a team to keep their plugin configurations in version control, so everyone has exactly the same configurations as anyone else on the team. No more "works on my machine but not on yours" weirdness. You can even manage them on a project-by-project basis, which is good.

But there are two aspects of working with multiple plugin configurations that are strange: specifically, creating and deleting them. In order to create an additional plugin configuration, you have to:

1. Create a folder to hold the configuration. It must be named "eclipse" and it must not be in Eclipse's directory structure.
2. Within your "eclipse" folder, you have to make an empty file called .eclipseextension, and two empty folders, features and plugins.

As Ford points out, Eclipse (inexplicably) won't do this for you. You have to do this by hand. It's not hard, just strange. At least this way you have more control over where the folders and files are located. (As I have multiple Eclipse installs, I used nesting to keep track of everything. I created a top-level folder called "eclipse-configurations"... under that, I made another folder for each of my named installs, and under each of those, I placed the "eclipse" folder as mentioned above. So, the versioned configuration for my "xquery" install of Eclipse is at /Users/haren/eclipse-configurations/xquery/eclipse.)

From there, you can go to Help -> Software Updates -> Manage Configuration and add your configuration location(s). Then it's a simple matter of installing your plugins to the config locations desired. You can then enable and disable multiple plugins as a group, switch between versions, etc. It's very handy.

But I'd mentioned that there were two strange things about the process. Creating additional configuration locations was one, deleting them was the second. Just as Eclipse gives you no love in creating them, it makes it even harder to get rid of them.

Let's say, for example, that you've added your new location as an extension not to the top-level list, but as an extension to an extension. (Yes, you can do this.) But let's also say that's not what you wanted. Well, you can disable your extension-within-an-extension, but you can't get Eclipse to ignore its existence entirely. If you then try to add it to the top level, Eclipse won't let you, complaining that you've already added it elsewhere. Arg.

Well, there's a way around that, too (but Ford doesn't mention it). Under ${ECLIPSE_HOME}/configuration/org.eclipse.update there's a file called platform.xml. Up at the top there are "site" nodes, and one of those will be your offender. Delete the bad guy and restart Eclipse. Now you can place your configuration elsewhere. (Or, you can just change the path in the node).

Anyway, as noted, there's a lot to gain by using multiple plugin configuarations, once you get around Eclipse's strange reluctance to make it intuitive. Happy hacking!

Windoze tools - Infra Recorder

If you somehow find yourself on a Windows machine and need to burn an image (iso) to a cd or dvd then I recommend Infra Recorder. I've used it a year or two ago, but found it again today and have to say it is looking and working good.

Mojave Experiment - an open insult to Windows users

If you haven't heard of Microsoft's newest advertising venture called Mojave Experiment let me fill you in. It is an 'experiment' (their words not mine) in which Windows XP users are asked to test out a cutting edge new M$ OS. Well it turns out this is just Vista. The punchline is users loveVista, just give it a chance all you mean naysayers. Well I think users don't like Vista and for good reasons. That is why it has not caught fire like M$ thinks it should have. Well I feel safe saying the execs up in Redwood must have lost their shit, having drunk their own Kool-Aid far too long. For a thorough examination check out this article. Peace!

Installing CouchDB on Gentoo

So I recently installed CouchDB on Gentoo at work and I figured for others sake I would post clear concise directions.

Portage setup

You are going to want a Portage overlay in which to put your own ebuild scripts. Having such a place will keep separation between the core Gentoo ebuilds and stuff you dabble with. Lets start with adding your Portage overlay: 'sudo mkdir -p /usr/local/portage'. This is where we are going to put your custom ebuilds. If you are interested, look in '/usr/portage'. Here you will see a lot of ebuilds that come via Gentoo's network.

To notify Gentoo (more specifically Portage) of this new overlay you will want to add the following line into the '/etc/make.conf' file:

PORTDIR_OVERLAY="/usr/local/portage"

Next up we need to have a category. Categories separate ebuilds by function and or purpose. For instance the web Server Apache is found in the 'www-servers' category. You can maybe find it @ '/usr/portage/www-servers' on your machine. You can pick any category name you like for this exercise. I'm going to be using 'ottaway'. For the category create a folder in '/usr/local/portage', in my case I do 'sudo mkdir /usr/local/portage/ottaway'. Substitute 'ottaway' for the name of your category.

To make Portage aware of this new category I add the line 'ottaway' to the '/etc/portage/categories' file.

Getting CouchDB

You will need to get the ebuild script for CouchDB. It is found as an attachment on this page. I used the following to download the script:

curl https://bugs.gentoo.org/attachment.cgi?id=159315 > couchdb-0.8.0.ebuild

You could pretty easily use wget also. I put this in my Portage overlay in my custom category @ '/usr/local/portage/ottaway', you must do the same for your category.

Next up you are going to have to tell Gentoo that you are ok with certain development ebuilds being installed. I did this by adding the following lines to the '/usr/portage/package.keywords' file:

# couchdb stuff
dev-lang/erlang
dev-util/svn2cl
dev-lang/spidermonkey
ottaway/couchdb ~x86

You can put those lines anywhere in the file. If you used a category name other than 'ottaway' change the value in the last line of the example above.

Next up I was ready to install the whole thing. You can do so using:

sudo emerge =<yourcategory>/couchdb-0.8.0

Where <yourcategory> is the name you gave your category you created earlier. Once this starts moving you can sit back and relax. When it finishes you can use "sudo -u couchdb couchdb" to get things started. When you see the "time to relax" pop onto the screen go ahead and hit your instance @ http://<yourdomain>:5984/_utils/index.html, where <yourdomain> is the network name of the machine CouchDB is running on.