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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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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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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Grails 3 is based on Spring Boot. This means we get a lot of the functionality of Spring Boot into our Grails applications. A Spring Boot application has by default a banner that is shown when the application starts. The default Grails application overrides Spring Boot's behavior and disables the display of a banner. To add a banner again to our Grails application we have different options.

First we can add a file banner.txt to our classpath. If Grails finds the file it will display the contents when we start the application. Let's add a simple banner with Grails3 in Ascii art in the file src/main/resources/banner.txt. By placing the file in src/main/resources we can assure it is in the classpath as classpath:/banner.txt:

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Java 8 introduced lambda expressions we can use for example with the new Java Streams API. The Groovy syntax doesn't support the lambda expressions, but we can rely on closure coersion to use Groovy closures as Java lambda expressions in our code.

In the following sample we use the Java Streams API. Instead of lambda expressions for the filter and map methods we use Groovy closures. They are automatically transformed to lambda expressions, so it is very easy to use Java streams from Groovy code.

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So this year I got the opportunity to speak and visit Greach 2015 in Madrid, Spain. I've never been in Spain before, but after visiting I definitely want to go back. Although the trip to Madrid was more cumbersome than planned, because of the strikes in France, I arrived at the speaker's dinner on time. Just go to mention that the Madrid metro is a very pleasant way to go around in Madrid. It was good to see old and new faces and to catch up and just have fun. Friday April 10th was the first day of the conference. The conference is held at the university in the south of Madrid. Jochen Theodorou, one of the Groovy core developers, opened the day with the keynote about Groovy's past, present and future. He gave a very nice overview of how Groovy evolved over the years and Groovy has been around already for a long time. Of course the latest news this year is Pivotal's hands off of Groovy and Grails. Jochen explained he first gets a good vacation and then decides what to do himself. Groovy is now in the process of getting an Apache project so the continuity of the development of the language should be saved. Then the rest of the day two tracks were presented at the same time. And there were difficult choices to make. Fortunately all talks are recorded and they will be added to the Greach Youtube channel.

I went to the talk Groovy and Scala: Friends or Foes by Marco Vermeulen. He showed how we can use Spock with Groovy to test Scala code using a Gradle build. So both worlds can live together and we can intermingle where possible. The application written in Scala was pragmatic and that is something I missed when I looked at Scala for the first time. This talk really got me interested to learn more about Scala. Next up was the talk AST - Groovy Transformers: More than meets the eye! by one of the conference organizers Iván López. He showed a lot of the (local) AST transformation that are already available in Groovy and that we can use everyday in our programs. Each AST transformation was clearly explained and he showed samples on how to use them. After his talk it was my time to present Grails Goodness. In this talk I live coded a selection of the blog posts about Grails I did write. Somehow there is always to little time to show everything I wanted, but still I think I was able to show some nice features of Grails.

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In Groovy we can use the sort and unique methods to sort a collection or remove duplicates from a collection. These methods alter the collection on which they are invoked. This is a side effect we might want to avoid. Therefore the sort and unique methods where changed and we could pass a boolean argument to indicate if the original collection should be changed or that we must have a new collection as the result of the methods, leaving the original collection untouched. Since Groovy 2.4 we have two new methods which by default return a new collection: toSorted and toUnique.

In the following sample we see the new methods in action:

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Since Groovy 2.4.0 we can get the indices from the elements in a collection with the indices method. In addition to this method we can also use the withIndex to combine an Iterable with the indices directly. The output is a List of tuples where the first item is the value of the Iterable and the second the index value. We can pass an optional argument to the withIndex which is the starting point for the index values. Another alternative is the indexed method. The indexed method returns a Map, where the key of the entry is the index value and the entry value is the Iterable value.

In the following example we use the withIndex method. The sample of the alphabet is the same as in the blog post about indices, but rewritten with the withIndex method:

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