Auto-generation of UML Class Diagrams in Maven Projects

The yWorks UML Doclet is a handy Javadoc extension that automatically creates good-looking UML diagrams from Java classes and embeds them into the generated API documentation.

Although the tool is not free sofware, it’s Community Edition is available for free of charge under the following conditions:

The Community Edition of the Software is licensed to you free of charge. It comes without support and warranties of any kind. The Community Edition of the Software inserts a web link into your output files that points to the yWorks website. You may not change that link or prevent either display of the link or the intended use as means of navigation to get to the yWorks website in any way.

These terms are quite reasonable and you don’t have to pay a high price for such a great tool.

The functionality offered by the product is also available in Apache Maven projects via the Maven Javadoc Plugin. The following is a minimal POM that demonstrates how to use the doclet in Maven projects:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>my</groupId>
  <artifactId>project</artifactId>
  <packaging>jar</packaging>
  <version>1.0</version>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-site-plugin</artifactId>
        <version>3.0</version>
        <configuration>
          <reportPlugins>
            <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-project-info-reports-plugin</artifactId>
            </plugin>
            <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-javadoc-plugin</artifactId>
              <version>2.8.1</version>
              <configuration>
                <doclet>ydoc.doclets.YStandard</doclet>
                <docletPath>${yDoc.path}/lib/ydoc.jar:${yDoc.path}/lib/styleed.jar:${yDoc.path}/resources</docletPath>
                <additionalparam>-umlautogen</additionalparam>
              </configuration>
            </plugin>
          </reportPlugins>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Can’t wait to try it? Download and unpack the archive of the Community Edition, then run Maven with mvn site -DyDoc.path=PATH where PATH is the path of the directory that contains your yDoc installation. Alternatively, the path can also be given in the properties element of the POM:

<properties>
  <yDoc.path>PATH</yDoc.path>
</properties>

The screenshot below shows the appearance of the enhanced API documentation.

API documentation with auto-generated UML class diagram

Thanks to László Aszalós for recommending this excellent tool.