In Scala, filtering and processing collections is easy and elegant. There are many filtermethods available, but the most used will probably the basic filter method. Here's a code example of some filtering on my (ex)camera collection. The filter method will not only work on Lists, but on any Scala collection.

object MyCameraCollection02 {

  case class Camera(brand: String, model: String, sensorType: String, yearBought: Int) {
    override def toString: String =
      s"$brand $model \t\t $sensorType \t($yearBought)"
  }

  def main(args: Array[String]) {
    val canon5dmarkIII = new Camera("Canon", "5D MkIII", "FF", 2013)
    val canon5dmarkII = new Camera("Canon", "5D MkII", "FF", 2009)
    val canon6d = new Camera("Canon", "6D", "FF", 2014)
    val canon550d = new Camera("Canon", "550D", "APS-C", 2010)
    val canon40d = new Camera("Canon", "40D", "APS-C", 2008)
    val canonIXUS330 = new Camera("Canon", "IXUS 330", "1/2.7", 2001)
    val canonIXUSZ90 = new Camera("Canon", "IXUS Z90", "APS-C", 1999)
    val panasonicGM1 = new Camera("Panasonic", "GM1", "M43", 2014)
    val panasonicFZ20 = new Camera("Panasonic", "FZ20", "1/2.5", 2005)
    val sonyrx100 = new Camera("Sony", "DSC-RX100", "1\"", 2013)
    val sonynex5 = new Camera("Sony", "NEX-5", "APS-C", 2011)
    val sonyr1 = new Camera("Sony", "DSC-R1", "APS-C", 2005)

    val myCameras = List(canon5dmarkIII, canon5dmarkII, canon6d, canon550d, canon40d, canonIXUS330, canonIXUSZ90, panasonicGM1, panasonicFZ20, sonyrx100, sonynex5, sonyr1)
    val canonCameras = myCameras filter (_.brand == "Canon") // Every Canon camera I ever owned
    val sonyCameras = myCameras filter (_.brand == "Sony") // Every Sony camera I ever owned
    val pansonicCameras = myCameras filter (_.brand == "Panasonic") // Every Panasonic camera I ever owned


    // apscCamera's only
    val apscCameras = myCameras filter (_.sensorType == "APS-C")
    println("==APS-C camera's owned==")
    apscCameras foreach println
    println()


    // Canon camera's which are not full frame. You can filter, filtered lists.
    val canonNonFF = myCameras filter (_.brand == "Canon") filter (_.sensorType != "FF")
    println("==Non-FF camera's owned==")
    canonNonFF foreach println
    println()

    // Filter by boolean expressions on class properties
    val apsBefore2012 = apscCameras filter (_.yearBought < 2012)
    println("==APS-C camera's bought before 2012 owned==")
    apsBefore2012 foreach println
    println()

    // Filter by combining boolean expressions.
    val ffcamerasBefore2012 = myCameras filter (cam => cam.yearBought < 2012 && cam.sensorType == "FF")
    println("==Every FF Camera I ever owned before 2012==")
    ffcamerasBefore2012 foreach println
    println()
  }
}

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In Gradle we can configure how duplicate files should be handled by the Copy task. Actually we can configure how duplicate files are handled by any task that implements the CopySpec interface. For example archive tasks also implements this interface. We must use the setDuplicatesStrategy method to configure how Gradle behaves. The parameter is a value of the enumeration DuplicatesStrategy. We can use the values from the enum class or use String values, which are automatically converted to enum DuplicatesStrategy values.

We can choose the following strategies:

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The nice thing about Gradle is that we can use Java libraries in our build script. This way we can add extra functionality to our build script in an easy way. We must use the classpath dependency configuration for our build script to include the library. For example we can include the library Grgit, which provides an easy way to interact with Git from Java or Groovy code. This library is also the basis for the Gradle Git plugin.

In the next example build file we add the Grgit library to our build script classpath. Then we use the open method of the Grgit class. From the returned object we invoke the head to get the commit id identified as id. With the abbreviatedId property we get the shorter version of the Git commit id. The build file also includes the application plugin. We customize the applicationDistribution CopySpec from the plugin and expand the properties in a VERSION file. This way our distribution always includes a plain text file VERSION with the Git commit id of the code.

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Scala has no default way to deal with dates and times. We have a few options. java.util.Date and java.util.Calendar These come included with java, so they may do if you don't need to do much and don't want to add any dependencies. But they're horrible and it's best not to use them. Joda-Time http://www.joda.org/joda-time/ The de facto standard date and time library for Java. nscala-time https://github.com/nscala-time/nscala-time A thin scala layer around Joda-Time. This adds some implicit conversions to make it easier to use, like the + and < operators.

import com.github.nscala_time.time.Imports._
DateTime.now + 2.months // returns org.joda.time.DateTime

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When we convert our Asciidoctor markup to HTML we automatically get a head and footer element. We can add custom content to the HTML head element and to the HTML div with id footer. We must set a document attribute and create the files that contain the HTML that needs to be added to the head or footer. We have three different document attributes we can set to include the custom content files:

• :docinfo: include document specific content. Files to be included must be named <docname>-docinfo.html for head element and <docname>-docinfo-footer.html for footer content.
• :docinfo1: include general custom content. Files to be included must be named docinfo.htmtl for head element and docinfo-footer.html for footer content.
• :docinfo2: include document specific and general custom content. Files to be included must be named <docname>-docinfo.html and docinfo.html for head element and <docname>-docinfo-footer.html and docinfo-footer.html for footer content.

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For Java or Groovy projects we can use the application plugin in Gradle to run and package our application. The plugin adds for example the startScripts task which creates OS specific scripts to run the project as a JVM application. This task is then used again by the installDist that installs the application, and distZip and distTar tasks that create a distributable archive of the application. The startScripts tasks has the properties unixScript and windowsScript that are the actual OS specific script files to run the application. We can use these properties to change the contents of the files.

In the following sample we add the directory configuration to the CLASSPATH definition:

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Grails 3 is based on Spring Boot. This means we can use a lot of the stuff that is available in Spring Boot now in our Grails application. If we look at the logging of a plain Spring Boot application we notice the logging has colors by default if our console supports ANSI. We can also configure our Grails logging so that we get colors.

First we need to change our logging configuration in the file grails-app/conf/logback.groovy:

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In Spring we can use the @Value annotation to set property or arguments values based on a SpEL expression. If we want to use the @Value annotation for a constructor argument we must not forget to add the @Autowired annotation on the constructor as well.

// File: sample/Message.groovy
package sample

import org.springframework.beans.factory.annotation.*
import org.springframework.stereotype.*

@Component
class Message {

    final String text

    // Use @Autowired to get @Value to work.
    @Autowired
    Message(
        // Refer to configuration property
        // app.message.text to set value for
        // constructor argument text.
        @Value('${app.message.text}') final String text) {
        this.text = text
    }

}

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One of the coolest things a standard Scala install will give you, is the Scala interpreter. Technically speaking, this is not an interpreter. In the background, each statement is quickly compiled into bytecode and executed on the jvm. Therefore, most people refer to it as the Scala REPL: Read-Evaluate-Print-Loop. You can access it by starting a command shell on your system and typing in 'scala'. Do make sure your either run it from the place where scala is installed or have scala on your environment PATH. By using the repl, you can quickly experiment and test out different statements. Once you press ENTER it will evaluate the statement and display the result. Frequently you want to execute multi-line statements and luckily the repl has a solution for that. Simply type in :paste and the repl will accept multiline statements. To exit this mode and evaluate your code, simply type CTRL+D. Example:

$ scala
Welcome to Scala version 2.11.4 (Java HotSpot(TM) Client VM, Java 1.7.0\_75).
Type in expressions to have them evaluated.
Type :help for more information.

scala> :paste
// Entering paste mode (ctrl-D to finish)

class Camera {

//this is a multiline example in the REPL

 val brand:String = "Canon"
 val model:String = "5D mark III"
}

// Exiting paste mode, now interpreting.

defined class Camera

scala> val cam = new Camera
cam: Camera = Camera@bfd117

scala> cam.brand
res0: String = Canon

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A good thing in Grails is that in Grails artifacts like controllers and services we have a log property to add log statements in our code. If we want to have the output of these log statements we must use a special naming convention for the log names. Each logger is prefixed with grails.app followed by the Grails artifact. Valid artifact values are controllers, services, domain, filters, conf and taglib. This is followed by the actual class name. So for example we have a controller SampleController in the package mrhaki.grails then the complete logger name is grails.app.controllers.mrhaki.grails.SampleContoller.

The following sample configuration is for pre-Grails 3:

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