Quick templating with gmaven and GStringTemplateEngine

16.06.2021 by Dirk Olmes

At work I have come across the requirement to generate some files based on the info in a pom.xml. Maven’s resource filtering feature would be the first thing that comes to mind but unfortunately it’s not powerful enough for my use case. I had to generate a file based on the dependencies that are referenced in the project.

A bit of googling found all kinds of outdated or unsupported maven plugins but nothing that would fit my use case directly. Finally I gave up and started to hack something together in groovy.

As it turns out groovy comes with a templating engine built in: groovy.text.GStringTemplateEngine. Using it is fairly straightforward from Maven:

....
<plugin>
    <groupId>org.codehaus.gmaven</groupId>
    <artifactId>groovy-maven-plugin</artifactId>
    <version>2.1.1</version>
    <executions>
        <execution>
            <phase>generate-resources</phase>
            <goals>
                <goal>execute</goal>
            </goals>
            <configuration>
                <source>${project.basedir}/templateGenerator.groovy</source>
            </configuration>
        </execution>
    </executions>
</plugin>

The templateGenerator.groovy Script is only a few lines long:

import java.io.File
import groovy.text.GStringTemplateEngine

def templateFile = "${project.basedir}/template.file" as File
def outputFile = "${project.build.directory}/dependencies.html" as File
outputFile.newWriter("UTF-8").withCloseable { writer ->
    def engine = new GStringTemplateEngine()
    def replacements = [ dependencies: project.dependencies ]
    engine.createTemplate(templateFile).make(replacements).writeTo(writer)
}

The template file can contain any syntax that the GStringTemplate supports.

IMHO this approach supports the best of both worlds: with only a little groovy scripting magic you get the maximum flexibility of a templating engine that has access to all the internals of your project.


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