Question

I have a Java program that generates Java classes for my application.
Basically it takes in a simple spec for a class and generates a specialized
form of Java bean. I want to integrate this into my Maven pom.xml so
that if the input file is changed, Maven automatically generates the
new .java file before the compile phase of Maven.

I know how to do this trivially in make but I didn’t find anything
in the Maven doc with this functionality.

Answer 1

You didn’t provide much details on your code generation process but you could maybe simply invoke the code generator with the exec-maven-plugin (see the Examples section). The convention is to generate sources in ${project.build.directory}/generated-sources/<tool>. Then add the generated sources with the build-helper-plugin and its add-sources mojo. Bind every thing on the generate-sources phase.

I’ll just show the build-helper stuff below:

<project>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <executions>
          <execution>
            <id>add-mytool-sources</id>
            <phase>generate-sources</phase>
            <goals>
              <goal>add-source</goal>
            </goals>
            <configuration>
              <sources>
                <source>${project.build.directory}/generated-sources/mytool</source>
              </sources>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

You could also write a simple plugin to wrap your generator. In that case, have a look at the Guide to generating sources.

PS: I may have missed something, there is a kind of mismatch between my answer and the title of your question.