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author Dirk Olmes <dirk.olmes@codedo.de>
date Wed, 16 Jun 2021 16:40:17 +0200
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1 Title: Quick templating with gmaven and GStringTemplateEngine
2 Date: 2020-06-16
3 Lang: en
4
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.
6
7 A bit of googling found all kinds of outdated or unsupported maven plugins but nothing that would fit my use case directly.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.
8
9 As it turns out groovy comes with a templating engine built in: `groovy.text.GStringTemplateEngine`. Using it is fairly straightforward from Maven:
10
11 :::xml
12 ....
13 <plugin>
14 <groupId>org.codehaus.gmaven</groupId>
15 <artifactId>groovy-maven-plugin</artifactId>
16 <version>2.1.1</version>
17 <executions>
18 <execution>
19 <phase>generate-resources</phase>
20 <goals>
21 <goal>execute</goal>
22 </goals>
23 <configuration>
24 <source>${project.basedir}/templateGenerator.groovy</source>
25 </configuration>
26 </execution>
27 </executions>
28 </plugin>
29
30 The `templateGenerator.groovy` Script is only a few lines long:
31
32 :::java
33 import java.io.File
34 import groovy.text.GStringTemplateEngine
35
36 def templateFile = "${project.basedir}/template.file" as File
37 def outputFile = "${project.build.directory}/dependencies.html" as File
38 outputFile.newWriter("UTF-8").withCloseable { writer ->
39 def engine = new GStringTemplateEngine()
40 def replacements = [ dependencies: project.dependencies ]
41 engine.createTemplate(templateFile).make(replacements).writeTo(writer)
42 }
43
44 The template file can contain any syntax that the [GStringTemplate](https://docs.groovy-lang.org/latest/html/api/groovy/text/GStringTemplateEngine.html) supports.
45
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.