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+++ b/content/Maven/gmaven-string-template-engine.md	Wed Jun 16 16:40:17 2021 +0200
@@ -0,0 +1,46 @@
+Title: Quick templating with gmaven and GStringTemplateEngine
+Date: 2020-06-16
+Lang: en
+
+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.
+
+A bit of googling found all kinds of outdated or unsupported maven plugins but nothing that would fit my use case directly.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:
+
+    :::xml
+    ....
+    <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>${project.basedir}/templateGenerator.groovy</source>
+                </configuration>
+            </execution>
+        </executions>
+    </plugin>
+
+The `templateGenerator.groovy` Script is only a few lines long:
+
+    :::java
+    import java.io.File
+    import groovy.text.GStringTemplateEngine
+
+    def templateFile = "${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](https://docs.groovy-lang.org/latest/html/api/groovy/text/GStringTemplateEngine.html) 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.