maven-archetype-plugin/src/site/apt/specification/archetype-metadata.apt

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 Archetype Metadata
 ------
 Raphaël Piéroni
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 2011-09-30
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~~ to you under the Apache License, Version 2.0 (the
~~ "License"); you may not use this file except in compliance
~~ with the License.  You may obtain a copy of the License at
~~
~~     http://www.apache.org/licenses/LICENSE-2.0
~~
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~~ software distributed under the License is distributed on an
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~~ KIND, either express or implied.  See the License for the
~~ specific language governing permissions and limitations
~~ under the License.

~~ NOTE: For help with the syntax of this file, see:
~~ http://maven.apache.org/doxia/references/apt-format.html


How is metadata about an archetype stored?

    The metadata about an archetype is stored in the <<<archetype-metadata.xml>>> file
    located in the directory <<<META-INF/maven>>> of its JAR file, see the
    {{{../../archetype-models/archetype-descriptor/archetype-descriptor.html}reference documentation}}.

    The metadata file stores the additional properties, with corresponding
    default values.

    It also stores the project's generated files in filesets.

    Finally it also stores inner modules of the archetype, which enable the
    creation of multi-module projects using a single archetype.

    A minimal <<<archetype-metadata.xml>>> file looks like:

+---
<?xml version="1.0" encoding="UTF-8"?>
<archetype-descriptor name="basic">
  <fileSets>
    <fileSet filtered="true" packaged="true">
      <directory>src/main/java</directory>
      <includes>
        <include>**/*.java</include>
      </includes>
    </fileSet>
  </fileSets>
</archetype-descriptor>
+---

    This example above shows:

    * the archetype name is <<<basic>>>

    * the archetype defines a single fileset:

      * the fileset will take all the files in <<<archetype-resources/src/main/java>>>
        that match the <<<**/*.java>>> pattern

      * the selected files will be generated using the Velocity engine
        (<<<filtered=true>>>)

      * the files will be generated in the <<<src/main/java>>> directory of the
        generated project in the same directory as in the JAR file, but with
        that directory prepended by the <<<package>>> property.

      []

    []


* Defining additional properties

    The main properties that are used by the Velocity engine during a project's file generation are groupId, artifactId, version and package.

    It is possible to define additional properties that must be valued before the file generation.

    These additional properties can be provided with default values, which enable not to ask the user for there values.

    Additional properties are defined in the <<<archetype-metadata.xml>>> file with:

+---
<archetype-descriptor name="basic">
  <requiredProperties>
    <requiredProperty key="property-with-default">
      <defaultValue>default-value</defaultValue>
    </requiredProperty>
    <requiredProperty key="property-without-default"/>
  </requiredProperties>
...
</archetype-descriptor>
+---

    Here two additional properties are defined: <<<property-with-default>>>
    and <<<property-without-default>>>.

    <<Note:>> The property keys can not contain any dots as they are
    Velocity properties.


* Defining specific filesets

    The filesets contained in the <<<archetype-metadata.xml>>> file defines the way
    the project's files located in the JAR file are used by the Archetype Plugin
    to generate a project.

    Filesets must define the directory where the files will be searched for
    which is also the directory where the project's files will be generated.
    The first is the directory inside the archetype JAR file, the second is the
    directory in the generated project's tree.

    Filesets also defines the inclusion/exclusion of files "<à la>" Ant.
    This provide a powerful way to describe a large set of files to be selected
    for the generation process.

    Filesets can be filtered, which means the selected files will be used
    as Velocity templates. They can be non-filtered, which means the selected
    files will be copied without modification.

    Filesets can be packaged, which means the selected files will be
    generated/copied in a directory structure that is prepended by the package
    property. They can be non-packaged, which means that the selected files
    will be generated/copied without that prepend.

    A fileset is defined in the <<<archetype-metadata.xml>>> with this fragment:

+---
...
  <fileSets>
    <fileSet filtered="true" packaged="true">
      <directory>src/test/java</directory>
      <includes>
        <include>**/*.java</include>
      </includes>
      <excludes>
        <exclude>AllTest.java</exclude>
      </excludes>
    </fileSet>
  </fileSets>
...
+---

    This example shows a fileset that will select all the java files in the
    <<<src/test/java>>> directory of the archetype resources, except the
    <<<AllTest.java>>> file that is located at the root of this directory.

    This fileset is also packaged and filtered.


* Defining multiple modules in the archetype metadata

    Inner modules of an archetype are used to create a multi-module Maven
    project from a single archetype.

    Modules in the <<<archetype-metadata.xml>>> file are defined like this:

+---
<archetype-descriptor name="multi-module">
  <fileSets>
    ...
  </fileSets>
  <modules>
    <module name="SubProject" id="subproject" dir="sub-project">
      <fileSets>
        ...
      </fileSets>
    </module>
  </modules>
</archetype-descriptor>
+---

    In the example above, the archetype <<<multi-module>>> contains a module
    named <<<SubProject>>>. This module is located in the <<<sub-project>>>
    directory of the archetype. It also has the artifactId <<<subproject>>>.

    The attributes <<<name>>>, <<<id>>> and <<<dir>>> of the module are used to determine the
    directory where the generated module's files will appear. They also are used to
    determine the artifactId of the Maven project corresponding to this
    module.


* Putting it all together

    The <<<\<requiredProperties\>>>> element is only allowed as a child of
    <<<\<archetype-descriptor\>>>>.

    Modules are allowed in <<<\<archetype-descriptor\>>>> and in <<<\<modules\>>>> (no limit is
    given).

    <<<\<archetype-descriptor\>>>> and <<<\<modules\>>>> must define at least one <<<\<fileSet\>>>> each to
    be valid.

    It is possible to define default values for required properties by
    defining say the groupId and giving it a default:

+---
...
  <requiredProperties>
    <requiredProperty key="groupId">
      <defaultValue>com.company.department</defaultValue>
    </requiredProperty>
  </requiredProperties>
+---

    Filesets can be defined from the root directory of the module/project by
    having an empty <<<\<directory\>>>> element:

+---
    ...
    <fileSet filtered="true" packaged="true">
      <directory></directory>
      <includes>
        ...
      </includes>
      <excludes>
        ...
      </excludes>
    </fileSet>
+---