Simple Mavenization of existing Ant build files

Question

If you have an existing ant file, what is the best way to convert the project to Maven. I've checked out things like fAnt, but if I'm going to mess with this stuff, I might as well go full-bore for Maven. I expected something to exist that can just start the pom.xml for me based on the existing build.xml, but I haven't found anything yet. Suggestions?

Answer 1

I don't know any good automated way to do such a migration because things may just be too different so I would do it manually, step by step, and keep the existing ant build in parallel of the future new one until the whole migration is done (from both technical and human points of view).

First, refactor the existing Ant build to align it on Maven conventions:

• Make things modular: if your existing build is a big monolithic build producing several artifacts from a single source tree, break it down into separate modules, one for each artifact.
• Update directory structure: Maven comes with a standard directory layout and, while it is possible to customize this layout (i.e. to configure plugins for another layout), this is not really recommended and is more a source of troubles than benefits. So I'd move existing app sources, configuration files, tests, etc to match Maven's layout (e.g. src/main/java for application sources, etc).

Then, start to create the Maven build:

• Create POMs for each module: Create a POM, declare external libraries as Maven dependencies (maybe add them to a corporate repository, using an enterprise repository is a good practice in an enterprise context anyway), add dependencies between modules.
• Finalize the multi-modules build: Add parent(s) POM(s) and inheritance/aggregating relationships. Test that there is no regression with the created artifacts.

You could do this work in a separate VCS branch if you don't want to change anything until the work is done and create scripts to move things. And when ready, merge the Maven specific stuff and apply the scripts.

Answer 2

You could run the Ant script from Maven with the maven-antrun-plugin. Your pom.xml would look something like this:

<project>
  ...
  <build>
     <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-antrun-plugin</artifactId>
            <dependencies>
                <dependency>
                    <groupId>org.apache.ant</groupId>
                    <artifactId>ant-nodeps</artifactId>
                    <version>${ant-nodeps.version}</version>
                </dependency>
            </dependencies>
            <executions>
                <execution>
                    <id>init</id>
                    <phase>compile</phase>
                    <configuration>
                        <tasks>
                            <!-- Ant code goes here -->
                        </tasks>
                    </configuration>
                    <goals>
                        <goal>run</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </build>
</project>

That way you can start to move your dependencies into Maven, and reference them in the Ant script like so

${com.foo.bar:my-lib:jar}

Then just start slowly moving pieces of your Ant into pure Maven stuff.