blog.bloidonia.com

A collection of interesting code snippets, workflows or stuff that I'm worried I might forget before I need it.

[bloidonia]

groovy-stream updates and Java integration

So a quick post about the latest release (0.8.0) of groovy-stream.

In a nutshell, this update has removed a couple of things, and added support for using groovy-stream from Java.

Farewell to the old

So first up, the things that are gone. Firstly something that I keep coming back to and getting wrong is asSynchronized. Synchronizing Iterators is hard. And I got it wrong again, so it's gone (again)

Secondly a lot of the remove calls have been errr... removed as despite removing something, it was hard to tell what was going to be removed (as some iterators cache the next element internally when hasNext is called), so I've changed them to throw an UnsupportedOperationException to save confusion.

Thirdly, Stream no longer implements Iterable.

Iterable implies iterator() can be called multiple times to start iterating again. But with Stream, this wouldn't happen. SO again, it's been removed as a potential source of confusion.

And hello to the new!

As for what is new, it's the fact that you can now use groovy-stream from Java.

So, for a contrived example lets say we x which can be 1, 2 or 3, and y which can be 4, 5 or 6.

Then, we want to get all possible sums of x and y where the result is odd.

In Java, we can declare our map for x and y then, we can declare a Stream which adds these two together, and only returns the odd values:

Mmmm...delicious verbosity ;-)

Of course, this verbosity drops when you move to Java 8

Oh and btw, with Groovy, it's cleaner still (thanks to delegation, List and Map literals and boolean coercion)

Enjoy!

@tim_yates

[bloidonia]

caterpillar-case, camelCase and snake_case, oh my!

There's no support for UPPERCASE-CATERPILLAR-CASE unfortunately, but all the following should pass (here I've added a caseFormat method to String to make the code a bit more readable)

Have fun!

@tim_yates

[bloidonia]

A miniKanren in Groovy

Finally got a working implementation of a miniKanren in Groovy (I basically ported the ruby version that can be found here).

It interests me, as it allows you to write code like this:

That prints:

Obviously, this simplistic example could be done in native groovy like so:

And it's a bit clunky at present (need to encode and unencode numbers, etc), but it's nice to have it working.

@tim_yates

[bloidonia]

Changing body class in Grails

The solution is to use the pageProperty call to fetch the property from the view and inject it into the layout before the page is rendered (as documented here):

@tim_yates

[bloidonia]

groovy-common-extensions v0.5

Taken from Ruby, the tap method executes the closure using the object as the delegate - internally, it just calls self.with c and then it returns self.

This allows you to tap into a method chain:

@tim_yates

[bloidonia]

Rendering anti-aliased text over semi-transparent backgrounds in Java/Groovy

Another blog post that's more for me in the future so I don't forget ;-)

Thought it might be of use to someone else as well, so posted it here for posterity.

The image generated by that script looks like this

as you can see, where the text is over a pink translucent rectangle, it looks less than good...

Turns out the fix is to set the correct AlphaComposite setting before rendering the text like so:

Then, the result looks much, much nicer:

@tim_yates

[bloidonia]

Rock Paper Scissors with Groovy-stream

Anyway, on to the code

@tim_yates

[bloidonia]

Object destructuring with getAt in Groovy

One thing I only recently learned about Groovy is that by implementing the getAt method, you can destructure your Object via multiple assignment.

As an example, consider a class Vector2D which represents a two-dimensional vector:

This can be achieved by adding a getAt method to our original Vector2D class

(Made a slight update so that getAt returns Double rather than double otherwise we can't return null from the default switch case -- Thanks to +Juan Vazquez for spotting this mistake)

@tim_yates

[bloidonia]

Lazy squares using groovy-stream

Last night, I saw a post on my twitter feed titled "Why Functional Programming in Java is Dangerous" where the author tries to implement the clojure code

in a functional style in Java, then concludes that "Functional idioms in Java are performance bugs waiting to bite you" after trying to load all of the Integers Java can handle into an ArrayList.

This morning, I then saw the response post "Bad Programming in Java Is Dangerous" which shows how the required result can be achieved with a liberal use of Iterators.

I thought I'd give this a go with the groovy-stream library, and came up with the following code:

It's only when we call the collect method that we start generating integers from the initial stream.

Of course, you can do it a single line (though it gets a bit funky updating x)

@tim_yates

[bloidonia]

Groovy-stream library now on Maven

Buoyed by my success pushing the groovy-common-extensions library to maven, I pushed the groovy-stream library to maven as well, so it's now possible (without any messing around with @GrabResolver) to give the library a whirl.

Here's some examples for those unsure of that the library does:

@tim_yates

[bloidonia]

Groovy Common Extensions on Maven

Last week I pushed my groovy-common-extensions project to maven via sonatype using the brilliant Gradle Nexus plugin by @bmuschko

More extensions are described on the project page, and thanks to André Steingress and Dan Woods for their contributions!

@tim_yates

[bloidonia]

Groovy 2.0.6: Bugfix for @Immutable allows use of Clojure collections

A quick note to myself. I found a bug in Groovy 2.0.5 that prevented you having an Immutable class that contained one of either Clojure's PersistentList and PersistentVector.

The bug was fixed for Groovy 2.0.6, and I just tested it and it all works great (thanks Paul for the fix)

(code won't run in the GroovyConsole as clojure doesn't initialize properly, but runs fine from the command line)

I can't use @CompileStatic as it rightly complains the List doesn't have a cons method (line 11), but as PersistentList and PersistentVector don't have a common ancestor that allows the cons method, I'd have to do some fancy switching logic to get it to work with the fully qualified types and two different Lists variables.

Interesting also to see on the Jira page that Groovy 2.1.0 will allow you to specify property names that you guarantee are Immutable!

@tim_yates

[bloidonia]

Get up and running with GroovyFX on the Raspberry Pi

This Christmas, I received a Raspberry Pi from Santa, so thought I'd have a go at getting JavaFX running on it. Of course, due to my interest in all things Groovy, I decided to go straight for getting GroovyFX running. After a day or two of foozling around (and at least half a day getting distracted by the RASPBMC media centre), I succeeded so thought I would post the steps I took here so others can follow my path to GroovyFX happiness.

Writing an image to SD card

First off when you get your Pi, you need to prepare an SD card with an OS. I chose Raspbian “wheezy” as it's the one recommended for beginners, and it's based on the Raspbian optimised version of Debian, and containing LXDE, Midori, development tools and example source code for multimedia functions.

So, download the image from the Raspberry Pi downloads page, unzip it and write it to your SD card -- instructions are on that page, but I am on OS X and chose to use the RPi-SD card builder so there was less chance of me messing something up using the dd command ;-)

Once that's done, take the card out of your machine, put it into your Pi, plug it all in and switch on!

A bit of setup

Once your Pi boots, you'll be greeted with this:

The first thing to do is expand_rootfs. This allows you to use all of your SD card space (the image you wrote to it only opens up a small portion of the available room)

Then, select memory_split and give the GPU 128MB of memory to play with (as we're going to be messing with graphics).

Change your password if you want (the default is raspberry), and I ran update to make sure everything was nice and up to date.

I also ran overclock. By slowly going up one step at a time, I found I could run in high setting, but turbo caused my SD card to not load properly -- if this happens to you, hold SHIFT while booting, then run sudo raspi-config and set it back to the highest successful level

If ever you find yourself needing to go back to this menu at a later date, just type sudo raspi-config.

Now the last step for the setup, when you have rebooted and logged in, edit the file /boot/config.txt and uncomment the two lines:

This will force a 720p resolution, so will make the pixel count less when we start throwing stuff to the screen.

Then, reboot with sudo shutdown -r now and we're on to the next step... JAVA!

Installing Java

In late 2012, Oracle released the JDK 8 (with JavaFX) for ARM Early Access. So download the gzipped tar file from there, scp it across to your pi (or just download it via the midori browser found when you run startx to get the windowing system up), unpack it then copy the jdk1.8.0 folder somewhere sensible:

Then, edit ~/.bashrc and add the lines:

Now, enter source ~/.bashrc to load your changes and then typing java -version should present you with something like:

java version "1.8.0-ea" Java(TM) SE Runtime Environment (build 1.8.0-ea-b36e) Java HotSpot(TM) Client VM (build 25.0-b04, mixed mode)

Installing Groovy

For installing Groovy, I decided to give GVM a whirl as it seemed like (and indeed was) the simplest route to take. Simply type:

curl -s get.gvmtool.net | bash

Follow the on-screen instructions (there's only one -- to reboot or source a file), and then type:

gvm install groovy

That's it.  Groovy 2.0.6 is now installed... Don't believe me? Type groovy -version and you should see:

Groovy Version: 2.0.6 JVM: 1.8.0-ea Vendor: Oracle Corporation OS: Linux

Grabbing the GroovyFX repo

GroovyFX is hosted on Github so to grab the source, we're going to need to install git on our Pi. This is easy, just type apt-get install git-core and wait for it to finish.

Then, we can fetch our repo.

For the Pi, I needed to make 2 changes to the source code.

The first (shown here) to src/main/groovy/groovyx/javafx/GroovyFXEnhancer.groovy is that the JavaFX WebEngine class seems to fail to load as it cannot find any resources files available (I tried 2 locales, en_US and en_GB, both failed and I gave up)

The second (shown here) is that we are using a different version of JavaFX so need to change the gradle.properties file accordingly

Building GroovyFX on the Pi

All set, we can now just type:

At this point, you might want to go and get some lunch, phone some friends or do something else time consuming as this takes about 15-20 mins from cold to build. Unfortunately running the Gradle daemon doesn't help as the buildSrc in the groovyfx project does something funky to the paths to get the demos to run from gradle.

Our test script

So, going for the simplest example script, we have the following:

Which as you can see is the stock HelloGroovyFX example but with the width and height changed to match our Pis output, and a KeyPress handler so we can quit it

Running the test

And then we come to the final step, running the script. We need to set our classpath and tell javafx that we are using the eglfb profile, but that's simple too. Just run:

and you should see (after a bit of a startup wait) the GroovyFX text appear on your screen!

Hope this helps someone get started with GroovyFX on the Raspberry Pi!

@tim_yates

[bloidonia]

Automated Javadoc testing in a Gradle built Groovy project

One of the things I love about how Groovy is built, is that quite a few of the examples in the Javadoc are automatically tested when you run ./gradlew test

I wanted to add this to my groovy-common-extensions project, and was surprised at how little code was required to get it running.

First, we can use the groovy.util.JavadocAssertionTestSuite class that comes with Groovy. So into src/test/groovy we create a class JavadocPreTagTestSuite.groovy (or whatever you want to call it):

We also need to make sure the following dependencies are declared in build.gradle

Then, you can add <pre class="groovyTestCase"> blocks to your Javadoc and these will automatically be run by JUnit when the project is tested. Here for example is my NumericExtensionMethods class:

Hope this helps you get started if you fancy doing the same thing! Automatically tested documentation is cool!

@tim_yates

[bloidonia]

99 bottles using a groovy-stream

Saw a tweet from Rob Fletcher about the 99 bottles of beer song written in LOLcode

99 Bottles of Beer in #LOLCODE 99-bottles-of-beer.net/language-lolco… #nextbiglanguage /via @cressie176

— Rob Fletcher (@rfletcherEW) December 6, 2012

And decided to see what it would look like with a groovy-stream.

This is what I ended up with:

@tim_yates

[bloidonia]

Stripping Microsoft Word "Smart Quotes" out of text with Groovy

A good few years ago, I wrote a Java helper class to convert the most common of these symbols back into ASCII, and just recently I converted it to Groovy and thought I'd share.

It's not complete, there are bound to be loads of characters that are missed in the conversion, but it catches enough to be of use to me.

@tim_yates

[bloidonia]

Using Clojure and core.logic from Groovy

Lately I've been interested in core.logic, a Clojure library written by David Nolen that implements miniKanren in Clojure.

This is what I came up with (with help from the codehaus page on calling Clojure from Groovy)

As you can see, when the data goes in to the Clojure method, we need to call read-string on it to get it into a Clojure string, and when the List of Maps comes back out, the keys of each map are of type clojure.lang.Keyword, so we need to wrap our String keys with clojure.lang.Keyword.intern when querying.

Other than that, just a case of cut and paste.

When this script is run (not in the Groovy Console, as it struggles getting its classpath right), it prints the grandparent->parent->child family lines that have Michael (our parameter) as the parent.

@tim_yates