Jersey fails when creating uber jar with maven-assembly-plugin

If you look inside the MOXy jar, you will see a folder META-INF/services. In that folder, you will see a file named org.glassfish.jersey.internal.spi.AutoDiscoverable. The content of that file should be a single line

org.glassfish.jersey.moxy.json.internal.MoxyJsonAutoDiscoverable

What this file is for is to allow Jersey to discover the MoxyJsonAutoDiscoverable, which registers MOXy for Jersey. This service loader pattern allows Jersey to discover features and register them, without us having to register them ourselves.

The problem this poses when creating an uber jar is that there may be multiple jars with the same file, as different jars have different features to discover, but the file needs to be that exact name as that is how the service loader pattern works.

So you have a bunch of jars with the same file, but when you create the uber jar, you cannot have multiple files with the same name. It’s just not possible. So only one of the files gets put into the final jar. Which one.. who knows. But that means that if MOXy’s files is not that one file then its feature will not be auto-discovered, and we need to register it ourselves. So the classes are packaged in the uber jar, but the main feature component is just not registered. You could just register it yourself

jerseyServlet.setInitParameter("jersey.config.server.provider.classnames",
                               "org.glassfish.jersey.moxy.json.MoxyJsonFeature");

but what about all the other possible features that are possibly left out because their auto-discoverable file is not included?

For this reason, instead of the assembly plugin, you should use the maven-shade-plugin, which has transformers that allow us to concatenate the contents of service files into one file.

The configuration would look something like

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <version>2.3</version>
    <configuration>
        <createDependencyReducedPom>true</createDependencyReducedPom>
        <filters>
            <filter>
                <artifact>*:*</artifact>
                <excludes>
                    <exclude>META-INF/*.SF</exclude>
                    <exclude>META-INF/*.DSA</exclude>
                    <exclude>META-INF/*.RSA</exclude>
                </excludes>
            </filter>
        </filters>
    </configuration>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>shade</goal>
            </goals>
            <configuration>
                <transformers>
                    <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
                    <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                        <mainClass>com.example.YourApp</mainClass>
                    </transformer>
                </transformers>
            </configuration>
        </execution>
    </executions>
</plugin>

The ServicesResorceTransformaer is what concatenates the files. This particular configuration of the plugin was taking from the Dropwizard getting started. You may want to check that out for further explanation.

More Related Contents:

Leave a Comment Cancel reply