Automatic UML diagram generation for Maven projects

Documenting your project is an important part of good software development. Creating and maintaining UML diagrams is one of the things to do. Luckily, there is a maven plugin that does this automatically for you...

maven

To add the urm-maven-plugin to your maven project, add the following snippet to the <plugins> section of your pom.xml:

<plugin>
    <groupId>com.iluwatar.urm</groupId>
    <artifactId>urm-maven-plugin</artifactId>
    <version>1.4.8</version>
    <configuration>
        <outputDirectory>${project.basedir}/target</outputDirectory>
        <packages>
            <param>be.cylab.mark.server</param>
        </packages>
        <ignores>
        </ignores>
        <includeMainDirectory>true</includeMainDirectory>
        <includeTestDirectory>false</includeTestDirectory>
        <presenter>graphviz</presenter>
    </configuration>
    <executions>
        <execution>
            <phase>process-classes</phase>
            <goals>
                <goal>map</goal>
            </goals>
        </execution>
    </executions>
</plugin>

In this example:

• We use version 1.4.8 of the plugin. At the time of writing, there is also a version 2.0.0 but that did not appear to work for our project.
• You have to list the packages for which you want to create the diagram (be.cylab.mark.server in our example).
• You can choose to ignore classes from the produced diagram.
• The map goal of the plugin will be executed during the process-classes phase of the build process (right after the compile phase).

Now you can run the plugin using maven, for example:

mvn clean package

The UML graph will be saved in target/${project.name}.urm.dot

graphviz

urm-maven-plugin does not produce an image. It produces a graph description in one of three possible formats: graphviz (like in our example), plantuml or mermaid.

To create an image from this description, we need graphviz installed:

sudo apt install graphviz

clean

There is one caveat: urm-maven-plugin does not escape < and > characters, which will cause errors (Error: bad label format) when we try to convert to a png image.

So we first have to use sed to escape these characters:

sed -i 's/</\</g' target/server.urm.dot
sed -i 's/>/\>/g' target/server.urm.dot
sed -i 's/-\>/->/g' target/server.urm.dot

convert

Now we can use the dot program (part of graphviz) to create a png image:

dot -Tpng target/server.urm.dot -o target/server.urm.png

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