richardlog

Top-down or bottom-up architecture?

Fri, 21 Sep 2012 20:48:17 +0200

Slides of my talk at the Agile Software Architecture Symposium 2012 in Elst.

Exploring Kotlin, writing a simple spell checker

Sun, 15 Apr 2012 14:17:00 +0200

In my last blog I talked about exploring Kotlin, a JVM language in development by JetBrains. In this blog I’ll walk through a larger piece of Kotlin code.

Spell checker
The program we’re talking about is a simple spell checker. It reads a dictionary of words from a file (/usr/share/dict/words) into a set. Then it reads a sentence from stdin and checks if every word is in the dictionary. Finally it informs the user whether or not the sentence is spelled correctly, i.e. every word is known in the dictionary.

The spell checker is available on my GitHub. Take a moment to study the Java version, we’ll discuss the Kotlin version next.

Entry point
The Kotlin program has a main method, or in Kotlin terms a main function. This function instantiates the KotlinSpellChecker class. Notice how the ‘new’ keyword is absent in Kotlin.

The ‘checkSpelling’ function is called with an expression. In Java we probably would have used a ternary operator in this case. Kotlin has none, instead you specify an if/else expression in a single line. The return value is written to stdout with some syntactic sugar called string templates.

fun main(args : Array) {
    val defaultInput = "Kotlin is an island"
    val valid = KotlinSpellChecker().checkSpelling(if (args.size > 0) args[0] else defaultInput)
    println("Is the text valid? $valid")
}

Checking spelling
The function below receives a set of words from the ‘readDictionary’ function and stores it in a variable named ‘words’. I haven’t explicitly specified a type for this (immutable) variable since Kotlin is able to infer the type information.

For-loops in Kotlin have a slightly different syntax compared to Java. In this case we iterate over an array of strings but Kotlin for-loops can also iterate over plain strings.

fun checkSpelling(input : String) : Boolean {
   val words = readDictionary()
   for (word in input.toLowerCase().split(" ")) {
        if (!words.contains(word)) {
            println("$word is not in the dictionary");
            return false;
        }
   }
   return true;
}

Reading a file
The following code returns a java.util.HashSet which is initialized using the ‘hashSet’ function from the Kotlin standard library (stdlib). The higher-order ‘forEachLine’ function accepts a function literal which adds each word to the mentioned HashSet.

Finally see the third line of code. We don’t have to wrap the FileInputStream in a BufferedInputStream ourselves, instead we just call the ‘buffered’ function to do it for us. Here we see extension functions in action, ‘buffered’ is a generic extension function implemented in stdlib on Java’s InputStream class.

private fun readDictionary() : Set {
    val words = hashSet("kotlin") // add kotlin to dictionary
    val stream = FileInputStream(DICTIONARY_WORDS).buffered();
    try {
         val reader = InputStreamReader(stream, "UTF-8");
         reader.forEachLine( { words.add(it)} )
    } finally {
         stream.close();
    }
    return words;
}

You can fork the code off GitHub in case you want to play with it. There’s room for comments below. Update: discussion on Hacker News.

Exploring Kotlin

Sun, 08 Apr 2012 17:56:00 +0200

I’ve been exploring Kotlin recently. Kotlin is a new statically typed JVM language and was announced about half a year ago. This month JetBrains released its first milestone candidate which I decided to have a closer look at.

First of Kotlin is still in its early stages. A lot of things work pretty well (I’m especially impressed by the IDE support) but there are still numerous issues. I’ve hit a couple of bugs so far.

Features
I’ll highlight a few language features which I think are interesting (coming from Java).

Null-safety

    fun demoVars() {
        val first : String = "abc"
        first = "xyz" // error, variable is immutable
        var second = "abc"
        second = null // error, variable is mutable but non-nullable
        var third : String? = "abc"
        third = null  // ok, variable is marked as nullable ('?')

        foo?.bar?.baz // safe navigation
    }

Multi-line strings and string templates

    fun demoMultiLineTemplate() {
        val first = "john"
        val second = "doe"
        println("""
          First name: $first
          Second name: $second
        """)
    }

Higher-order functions

    bar({ println("I'm foobar") })
    bar({ println("I'm foobar") }, { println("I'm foobaz") })

    fun  bar(foobar : () -> T) {
        foobar()
    }

    fun  bar(foobar : () -> T, foobaz : () -> B) {
        foobar()
        foobaz()
    }

These a just some examples refer to the Kotlin docs for more features.

Next blog
In my next blog I’ll show a larger example of Kotlin code and compare it with its Java equivalent.

NoSQL techday

Tue, 27 Mar 2012 17:28:22 +0200

NoSQL techday:

Recap of the techday that I organized last week at Avisi.

Disabling caching in Apache Shindig

Wed, 14 Mar 2012 17:53:21 +0100

Disabling caching in Apache Shindig:

I’m currently working on a project that involves using Apache Shindig. As you may know Shindig relies heavily on caching. While generally a good thing caching is a pain during development. See my post at the Avisi blog on how to disable this in Shindig.

Putting Talend Open Studio projects under version control

Mon, 16 Jan 2012 10:00:06 +0100

When you are working on OS X - I’m not sure if other OS’es have the same issue - your Talend Open Studio workspace is located under

/Applications/TOS-<version>/TalendOpenStudio-macosx-carbon.app/Contents/MacOS/workspace

That’s right the workspace is placed inside TalendOpenStudio.app, which isn’t a very convenient place. Although Talend Open Studio is based on Eclipse it isn’t keen on moving your workspace to a different location. The easiest way around this issue is to replace the above workspace directory with a symlink:

ln -s ~/workspace

From now on all your Talend jobs are created in a workspace under your home directory. To put the contents of this workspace under version control I recommend the following principles (source: bowerstudios.com):

First, avoid Subversion/CVS as they will likely get you into trouble since they add info to each directory that is in version control. Talend Open Studio (TOS) tends to wipe out directories and recreate them, so you will have problems with those two tools complaining that they have lost information. Try to use a tool that does not add per directory entries (like git). I chose git.

You will need to enter the entire workspace into version control, including the hidden metadata and compilation directories (.metadata, .JETEmitters and .Java). With each commit, make sure you grab all of those files that have changed.

For each commit, do not commit until after you have exited TOS.

If sharing across platforms, or with other developers, you may need to keep track of the different paths on your machines:
For example, when you export a job, it will successfully export, but with previously compiled classes if the .classpath file in the .Java directory contains paths not on your local machine. Another way to put it, If someone else commits the project, you check it out, you make changes, you export it, the running code will not reflect the changes you made, even though the source does reflect those changes.

While versioning an entire workspace isn’t ideal it’s the one solution that’s guaranteed to work. If you can suggest better alternatives please let me know.

Finally to verify whether your workspace is still valid after performing the above, just open a job and click on the ‘code’ tab. If you see generated Java code you know your workspace isn’t corrupted.

Good luck!

Healthy RSS addiction

Fri, 13 Jan 2012 10:03:00 +0100

I’ve been a long term fan of RSS feeds. It’s ideal when following tech news. In the past I used to read my feeds on a computer - using a mail client - but nowadays I prefer my iPad.

The following screenshot from Google Reader shows my addiction over the past year.

Hmmm a little over 7 tech articles/blogs a day, that sounds about right. Although… this doesn’t include my reads on Hacker News. Perhaps it’s more serious than I thought ;)

Cross posted to http://blog.avisi.nl/2012/01/13/healthy-rss-addiction/

Has Facebook silently killed Open Streams in favor of Open Graph?

Sun, 11 Dec 2011 20:15:00 +0100

I was looking at the JSON Activity Stream specification today. Facebook is listed as one of the parties to support this format. Indeed I’ve found a blog post written in April 2009 that confirms Facebook has implemented JSON activity streams. Facebook calls it Open Streams.

In the meantime all references to the Open Streams developer documentation have been removed. Looking at the current Graph API it doesn’t seem to conform to the JSON activity stream 1.0 format. Did Facebook (silently) stopped supporting this format?

Integration testing RESTful services in Java

Tue, 22 Nov 2011 21:26:00 +0100

Integration testing RESTful services in Java:

Currently I’m using the build-in HTTP server in Java 6 for (integration) testing RESTful services. Although this has the advantage of adding zero dependencies, the API of REST-assured looks cleaner. Something to keep in mind when you need to test (many) services.

The Architecture of Open Source Applications

Wed, 16 Nov 2011 21:50:14 +0100

The Architecture of Open Source Applications:

This book is available for free online under the Creative Commons license.

Playing an agile learning game during scrum training (inspired...

Tue, 15 Nov 2011 22:52:00 +0100

Playing an agile learning game during scrum training (inspired by the XP game). It looks a bit like a kids party considering all the balloons and colored paper :). Useful exercise nonetheless, reminds me a bit about the software process course I attended while in university.

Pretty-printing JSON and XML on Mac OSX

Sun, 13 Nov 2011 18:02:00 +0100

Like my colleagues at Avisi I’m an avid OSX user. One of the reasons I like OSX is it gives you the power of Unix right under your fingertips while still providing a nice user interface.

Now suppose you’re working on RESTful services and you need to verify or debug some JSON output. Digging through an unformatted JSON string can be a real pain. To make a JSON string human readable open up the Terminal and type:

cat unformatted.json | python -m json.tool > formatted.json

This will pretty-print the contents of “unformatted.json” to a new file called “formatted.json”. For this to work you need to have at least Python 2.6 installed. Which is the case when your running Snow Leopard or higher.

The above command assumes you have a file containing the JSON content. When you’re debugging it’s more likely you copied a JSON string to your clipboard from a (remote) log file. To pretty-print the JSON content on your clipboard type:

pbpaste | python -m json.tool > formatted.json

Likewise when you’re dealing with XML instead of JSON type in:

pbpaste | xmllint --format - > formatted.xml

The xmllint program is part of libxml2 and installed by default on OSX.

Happing pretty-printing!

Update: Hacker News thread

Interesting extension of OpenSocial beyond web applications

Sun, 06 Nov 2011 11:58:34 +0100

Interesting extension of OpenSocial beyond web applications:

Xobni offers an OpenSocial container inside Outlook. One example of a useful gadget (at least one that I can relate to) is the JIRA gadget.

Got a brand new MacBook Pro thanks to Avisi. My previous MacBook...

Tue, 01 Nov 2011 19:13:00 +0100

Got a brand new MacBook Pro thanks to Avisi. My previous MacBook Pro in the back was a late 2008 model. This one should be a lot faster and it’s got Lion preinstalled :).

IntelliJ IDEA and Maven: M2_HOME trouble

Sun, 30 Oct 2011 14:55:00 +0100

There’s an annoying issue when using Maven from IntelliJ IDEA on OSX. You might encounter the following error when building a Maven project.

No valid Maven installation found. Either set the home directory in the configuration dialog or set the M2_HOME environment variable on your system.

The issue is well known and there are various solutions to the problem. The trouble with some is they apply to old versions of OSX, specifically Leopard. If your running Snow Leopard or higher you don’t need to alter your launchd configuration. The following will suffice:

1) Check you Maven home directory.

2) Create the following file in ~/.MacOSX/environment.plist.

{
"M2_HOME"="/usr/share/maven";
M2="/usr/share/maven/bin";
}

3) Make sure you enter the correct path as shown in the Maven version info.

4) Reboot your system (I know it’s annoying).

Now you should have no problem starting Maven builds from IDEA.

Amazon Web Services Architecture Center

Sat, 29 Oct 2011 13:00:00 +0200

Amazon Web Services Architecture Center:

Take a look at the references architectures in case your wondering how the different AWS services fit together.

"Extract until you can’t extract any further."

Sat, 22 Oct 2011 16:45:00 +0200

“Extract until you can’t extract any further.”

- Robert C. Martin, better known as Uncle Bob, talking about (refactoring) functions.

First post

Mon, 17 Oct 2011 22:45:00 +0200

Welcome to my new blog or more accurately “tumblelog”. Here I’ll occasionally share my experiences as a software engineer. Themes include Java, agile, open source, architecture and pretty much anything in between.