Apache FreeMarker Generator Maven Plugin

Table of contents

• Background
• Install
• Usage
  • FreeMarker Template Files
  • JSON Generator Files
  • Using POM Properties During Generation
  • FreeMarker Configuration
  • Incremental Builds
• Code Coverage

Background

This plugin generates source files from FreeMarker templates with a flexible process that includes the ability to:

• Generate multiple source files from a single template,
• Generate source files during multiple steps in the build process such as testing, and
• Specify distinct locations for the templates and data models for different stages of the build.

Install

pom.xml

Add the following snippet within the <plugins> tag of your pom.xml:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.freemarker.generator</groupId>
            <artifactId>freemarker-generator-maven-plugin</artifactId>
            <version>${project.version}</version>
            <configuration>
                <!-- Required. Specifies the compatibility version for template processing -->
                <freeMarkerVersion>${freemarker.version}</freeMarkerVersion>
            </configuration>
            <executions>
                <!-- 
                    If you want to generate files during other phases, just add more execution
                    tags and specify appropriate phase, sourceDirectory and outputDirectory values.
                -->
                <execution>
                    <id>freemarker-generator</id>
                    <!-- Optional, defaults to generate-sources -->
                    <phase>generate-sources</phase>
                    <goals>
                        <!-- Required, must be generate -->
                        <goal>generate</goal>
                    </goals>
                    <configuration>
                        <!-- Optional, defaults to src/main/freemarker/generator -->
                        <sourceDirectory>src/main/freemarker/generator</sourceDirectory>
                        <!-- Optional, defaults to src/main/freemarker/generator/template -->
                        <templateDirectory>src/main/freemarker/generator/template</templateDirectory>
                        <!-- Optional, defaults to src/main/freemarker/generator/generator -->
                        <generatorDirectory>src/main/freemarker/generator/generator</generatorDirectory>
                        <!-- Optional, defaults to target/generated-sources/freemarker/generator -->
                        <outputDirectory>target/generated-sources/freemarker/generator</outputDirectory>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Usage

FreeMarker Template Files

FreeMarker template files must reside in the templateDirectory. For the default configuration, this is: src/main/freemarker/generator/template.

By convention, file names for FreeMarker template files use the .ftl extension. For details on the FreeMarker template syntax, see: Getting Started and Template Language Reference.

JSON Generator Files

The JSON generator files must reside in the generatorDirectory. For the default configuration, this is: src/main/freemarker/generator/generator.

For each JSON generator file, freemarker-maven-plugin will generate a file under the outputDirectory. The name of the generated file will be based on the name of the JSON data file. For example, the following JSON file:

    <sourceDirectory>/data/my/package/MyClass.java.json

will result in the following file being generated:

    <outputDirectory>/my/package/MyClass.java

This plugin parses the JSON generator file's dataModel field into a Map<String, Object> instance (hereafter, referred to as the data model). If the dataModel field is empty, an empty map will be created.

Here are some additional details you need to know.

• This plugin requires one top-level field in the JSON data file: templateName. This field is used to locate the template file under <sourceDirectory>/template that is used to generate the file. This plugin provides the data model to FreeMarker as the data model to process the template identified by templateName.
• The parser allows for comments.
• This plugin currently assumes that the JSON data file encoded using UTF-8.

Here is an example JSON data file:

{
  // An end-of-line comment.
  # Another end-of-line comment
  "templateName": "my-template.ftl", #Required
  "dataModel": { #Optional
      /* A multi-line
         comment */
      "myString": "a string",
      "myNumber": 1,
      "myListOfStrings": ["s1", "s2"],
      "myListOfNumbers": [1, 2],
      "myMap": {
        "key1": "value1",
        "key2": 2
      }
  }
}

Using POM Properties During Generation

After parsing the JSON file, the plugin will add a pomProperties entry into the data model, which is a map itself, that contains the properties defined in the pom. Thus, your template can reference the pom property my_property using ${pomProperties.my_property}. If you have a period or dash in the property name, use ${pomProperties["my.property"]}.

FreeMarker Configuration

Typically, users of this plugin do not need to mess with the FreeMarker configuration. This plugin explicitly sets two FreeMarker configurations:

1. the default encoding is set to UTF-8
2. the template loader is set to be a FileTemplateLoader that reads from templateDirectory.

If you need to override these configs or set your own, you can put them in a <sourceDirectory>/freemarker.properties file. If that file exists, this plugin will read it into a java Properties instance and pass it to freemarker.core.Configurable.setSettings() to establish the FreeMarker configuration. See this javadoc for configuration details.

Incremental Builds

This plugin supports incremental builds; it only generates sources if the generator file, template file, or pom file have timestamps newer than any existing output file. To force a rebuild if these conditions are not met (for example, if you pass in a model parameter on the command line), first run mvn clean.

Code Coverage

By default, the code coverage report is not generated. It is generated by screwdriver jobs. You can generate code coverage on your dev machine with the following maven command:

mvn clean initialize -Dclover-phase=initialize 

Bring up the coverage report by pointing your browser to target/site/clover/dashboard.html under the root directory of the local repository.