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1 Title: Quick templating with gmaven and GStringTemplateEngine
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2 Date: 2021-06-16
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3 Lang: en
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4
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5 At work I have come across the requirement to generate some files based on the info in a `pom.xml`. Maven's [resource filtering](https://maven.apache.org/plugins/maven-resources-plugin/examples/filter.html) 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.
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6
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7 A bit of googling found all kinds of outdated or unsupported maven plugins but nothing that would fit my use case directly.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.
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8
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9 As it turns out groovy comes with a templating engine built in: `groovy.text.GStringTemplateEngine`. Using it is fairly straightforward from Maven:
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10
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11 :::xml
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12 ....
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13 <plugin>
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14 <groupId>org.codehaus.gmaven</groupId>
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15 <artifactId>groovy-maven-plugin</artifactId>
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16 <version>2.1.1</version>
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17 <executions>
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18 <execution>
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19 <phase>generate-resources</phase>
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20 <goals>
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21 <goal>execute</goal>
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22 </goals>
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23 <configuration>
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24 <source>${project.basedir}/templateGenerator.groovy</source>
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25 </configuration>
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26 </execution>
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27 </executions>
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28 </plugin>
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29
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30 The `templateGenerator.groovy` Script is only a few lines long:
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31
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32 :::java
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33 import java.io.File
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34 import groovy.text.GStringTemplateEngine
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35
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36 def templateFile = "${project.basedir}/template.file" as File
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37 def outputFile = "${project.build.directory}/dependencies.html" as File
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38 outputFile.newWriter("UTF-8").withCloseable { writer ->
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39 def engine = new GStringTemplateEngine()
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40 def replacements = [ dependencies: project.dependencies ]
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41 engine.createTemplate(templateFile).make(replacements).writeTo(writer)
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42 }
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43
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44 The template file can contain any syntax that the [GStringTemplate](https://docs.groovy-lang.org/latest/html/api/groovy/text/GStringTemplateEngine.html) supports.
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45
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46 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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