Eugene Burtsev's blog

Maven Custom Repository Layout

I’ve developed maven plugin to access repositories with custom structure. And I would share this solution with community.

Some time ago, I worked on java web project, and I used some JavaScript dependencies for it. I’ve throught about dependency management for javascript dependencies like JQuery. Ordinary JS dependencies is not management, so we need download new versions manually. First I found Bower for javascript dependency management, but I afraid of node.js in dependencies for my project. I thought about CDNs which hosts js libraries. (for example jquery on Google CDN: http://ajax.googleapis.com/ajax/libs/jquery/1.8.2/jquery.min.js). I using maven in my projec, so it will be good to use CDNs via maven… Because CDN’s directories stricture is differs from standart maven layout, I decided to write own maven plugin to handle custom repository layout.

When I looked for solution I found that maven allows write plugins which handles custom repository types. But I found too less examples how to do it. I found only one thing: for create custom repository handler we needs to implement RepositoryConnectorFactory interface. I’ve created simple calss to test this approach:

CustomRepositoryConnectorFactory.java
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@Component(role = RepositoryConnectorFactory.class, hint = "custom")
public class CustomRepositoryConnectorFactory implements RepositoryConnectorFactory, Service {

        @Override
        public RepositoryConnector newInstance(RepositorySystemSession session,
                RemoteRepository repository) throws NoRepositoryConnectorException {
                System.out.println("CustomRepositoryConnectorFactory.newInstance()");
                return null;
        }

        @Override
        public int getPriority() {
                return 1;
        }

        @Override
        public void initService(ServiceLocator locator) {

        }
}

But this has not worked. To make it work we also need to generate maven component description in META-INF/plexus/components.xml file. To create this file there is plexus-component-metadata plugin, which parses annotations and creates this magic file.

components.xml
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    <plugin>
            <groupId>org.codehaus.plexus</groupId>
            <artifactId>plexus-component-metadata</artifactId>
            <version>1.5.5</version>
            <executions>
                    <execution>
                            <goals>
                                    <goal>generate-metadata</goal>
                            </goals>
                    </execution>
            </executions>
    </plugin>

After components.xml generated and I installed plugin in my local repository all worked fine.

How to use it. First, add my maven repo in your pom.xml (for a while I host it in my own repo, but in future I want to move it to Maven Central):

pom.xml
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<pluginRepositories>
  <pluginRepository>
      <id>maven-burtsev-net</id>
      <url>http://maven.burtsev.net</url>
  </pluginRepository>
</pluginRepositories>

Enable plugin in build section of pom.xml:

pom.xml
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<build>
  <extensions>
      <extension>
          <groupId>net.burtsev.maven</groupId>
          <artifactId>maven-custom-repository-layout</artifactId>
          <version>1.0</version>
      </extension>
  </extensions>
</build>

Add some repositories, for example:

pom.xml
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<repository>
  <id>google-cdn</id>
  <url>http://ajax.googleapis.com/ajax/libs/$groupId/$version/$artifactId${classifier(prefix:.)}.$extension</url>
  <layout>custom</layout>
</repository>

In repository URL we can use following wildcards which will replaced with appropriate values for each artifact:

  • $groupId
  • $artifactId
  • $version
  • $classifier
  • $extension

For parameter which can be empty there is alternate syntax: ${classifier(prefix:.)}. this syntax is useful for eliminate separators duplicates if value will empty.

After we configured repository we can add some dependencies, for example:

pom.xml
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<dependencies>
  <dependency>
      <groupId>jquery</groupId>
      <artifactId>jquery</artifactId>
      <version>1.8.2</version>
      <classifier>min</classifier>
      <type>js</type>
  </dependency>
</dependencies>

I’ve used maven-dependency-plugin to copy downloaded libraries to webapp folder:

pom.xml
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<plugins>
  <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-dependency-plugin</artifactId>
      <executions>
          <execution>
              <id>copy-dependencies</id>
              <phase>generate-resources</phase>
              <goals>
                  <goal>copy-dependencies</goal>
              </goals>
              <configuration>
                  <outputDirectory>${project.build.directory}/${project.build.finalName}/js</outputDirectory>
                  <includeArtifactIds>jquery</includeArtifactIds>
                  <includeTypes>js</includeTypes>
              </configuration>
          </execution>
      </executions>
  </plugin>
</plugins>

That is it. Now we can manage JS dependencies with maven.

Sources can be found here: https://bitbucket.org/eburtsev/maven-custom-repository-layout Plugin can be downloaded from my maven repository: http://maven.burtsev.net/ Sample project uses this plugin https://bitbucket.org/eburtsev/test-javascript-dependencies

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