Brizzled

... wherein I bloviate discursively

Brian Clapper, bmc@clapper.org

Generating a QR Code in Scala

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I recently discovered that I needed to generate QR codes in Scala, and it turns out to be quite simple, with the help of the QRGen Java library, by Ken Gullaxen.

In this brief article, I demonstrate how to create a simple SBT project to pull in the appropriate dependencies, as well as how to call the QRGen library from Scala.

QRGen is a front-end to the ZXing library provided by Zebra Crossing. QRGen makes generating QR codes trivial.

Step 1: Create an SBT project

I use Nathan Hamblen’s giter8 tool, along with Typesafe’s scala-sbt.g8 template:

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$ g8 typesafehub/scala-sbt
Scala Project Using sbt

organization [org.example]: org.clapper
name [Scala Project]: QRTest
scala_version [2.9.2]:
version [0.1-SNAPSHOT]:

Template applied in ./qrtest

giter8 creates a stub SBT project, including an initial SBT full build definition file. In this case, since I named the project QRTest, it created the project tree in subdirectory qrtest, and the build definition in qrtest/project/QrtestBuild.scala.

The initial contents of QrtestBuild.scala are:

Inital QrtestBuild.scala 
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import sbt._
import sbt.Keys._

object QrtestBuild extends Build {

  lazy val qrtest = Project(
    id = "qrtest",
    base = file("."),
    settings = Project.defaultSettings ++ Seq(
      name := "QRTest",
      organization := "org.clapper",
      version := "0.1-SNAPSHOT",
      scalaVersion := "2.9.2"
  )
}

Step 2: Add the library dependencies

Next, modify QrtestBuild.scala to depend on QRGen. To do so, simply add the QRGen Maven repository and the artifact, as shown in lines 14 through 16, below. Note that I’m also adding a dependency on my Grizzled Scala library, because it has a useful file copy routine.

Specifying QRGen dependency in QrtestBuild.scala 
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import sbt._
import sbt.Keys._

object QrtestBuild extends Build {

  lazy val qrtest = Project(
    id = "qrtest",
    base = file("."),
    settings = Project.defaultSettings ++ Seq(
      name := "QRTest",
      organization := "org.clapper",
      version := "0.1-SNAPSHOT",
      scalaVersion := "2.9.2",
      resolvers += "QRGen" at "http://kenglxn.github.com/QRGen/repository",
      libraryDependencies += "net.glxn" % "qrgen" % "1.1",
      libraryDependencies += "org.clapper" %% "grizzled-scala" % "1.0.13"

    )
  )
}

Step 3: Generate a QR code interactively

At this point, the SBT project is ready. There’s no code in it, other than the build file. However, we can use the SBT console to test generating a QR code. First, fire up SBT:

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$ sbt
[info] Loading global plugins from /home/bmc/.sbt/plugins/project
[info] Loading global plugins from /home/bmc/.sbt/plugins
[info] Loading project definition from /home/bmc/tmp/qrtest/project
[info] Updating {file:/home/bmc/tmp/qrtest/project/}default-7a3da4...
[info] Resolving org.scala-sbt#root;0.0 ...
...
[info] Compiling 1 Scala source to /home/bmc/tmp/qrtest/project/target/scala-2.9.2/sbt-0.12/classes...
[info] Set current project to QRTest (in build file:/home/bmc/tmp/qrtest/)
>

Then, bring up the Scala console:

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> console
[info] Updating {file:/home/bmc/tmp/qrtest/}qrtest...
[info] Resolving org.scala-lang#scala-library;2.9.2 ...
[info] Resolving net.glxn#qrgen;1.1 ...
[info] Resolving com.google.zxing#core;2.0 ...
[info] Resolving com.google.zxing#javase;2.0 ...
[info] Resolving jline#jline;2.6 ...
[info] Done updating.
[info] Compiling 1 Scala source to /home/bmc/tmp/qrtest/target/scala-2.9.2/classes...
[info] Starting scala interpreter...
[info] 
Welcome to Scala version 2.9.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_26).
Type in expressions to have them evaluated.
Type :help for more information.

scala>

And, now, we can fiddle:

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scala> import net.glxn.qrgen._
import net.glxn.qrgen._

scala> import grizzled.file.GrizzledFile._
import grizzled.file.GrizzledFile._

scala> val f = QRCode.from("http://brizzled.clapper.org/").file()
f: java.io.File = /tmp/QRCode5131788435518615347.png

scala> f.copyTo("/tmp/qr.png")
res0: java.io.File = /tmp/qr.png

That’s it: Four lines of code, including two import statements, to generate a QR code and save it to a file. Note that QRGen’s file() call saves the image to a temporary file that is deleted with the Java VM exits. The copyTo() call just saves it someplace more permanent.

Here’s the result:

For more information

QRGen has many more features. Check out the QRGen web page.

If you want to get into the detailed nitty gritty, you can bypass QRGen and go directly to the ZXing API. But QRGen is so easy, why bother?

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