ARTICLES

Don't export the same package as another bundle

Today I wanted to wire in the new GraphService into OpenNMS and have a graph:list command show a GraphML graph I sent to the /opennms/rest/graphml endpoint. The idea was to leverage the GraphmlRepository to also store a configuration file for a new GraphMLGraphContainerProviderServiceFactory implementing a ManagedServiceFactory. Basically the same as we already do with the GraphMLTopologyFactory

I wired everything together and was also able to install the features. However as soon as I send the graphml document to the rest endpoint via (of course OpenNMS should be started)

cd ~/dev/opennms/smoke-test
# Ensure it is not already existing
curl -v -X DELETE -u admin:admin http://localhost:8980/opennms/rest/graphml/test-graph
# wait a few seconds, then create the graph
curl -v -X POST -u admin:admin -H "Content-Type: application/xml" -d@src/test/resources/topology/graphml/test-topology.xml http://localhost:8980/opennms/rest/graphml/test-graph

In the karaf.log the following exception occurs sigh:

java.lang.NoClassDefFoundError: edu/uci/ics/jung/graph/DirectedSparseGraph
	at org.opennms.features.graph.api.AbstractGraph.<init>(AbstractGraph.java:50) ~[?:?]
	at org.opennms.features.graph.api.generic.GenericGraph.<init>(GenericGraph.java:74) ~[?:?]
	at org.opennms.features.graph.providers.graphml.GraphmlGraphContainerProvider.convert(GraphmlGraphContainerProvider.java:136) ~[?:?]
	at org.opennms.features.graph.providers.graphml.GraphmlGraphContainerProvider.loadGraphContainer(GraphmlGraphContainerProvider.java:117) ~[?:?]
	at org.opennms.features.graph.providers.graphml.GraphmlGraphContainerProvider.<init>(GraphmlGraphContainerProvider.java:87) ~[?:?]
	at org.opennms.features.graph.providers.graphml.GraphMLContainerProviderServiceFactory.updated(GraphMLContainerProviderServiceFactory.java:79) ~[?:?]
	at org.apache.felix.cm.impl.helper.ManagedServiceFactoryTracker.updated(ManagedServiceFactoryTracker.java:159) ~[8:org.apache.felix.configadmin:1.8.16]
	at org.apache.felix.cm.impl.helper.ManagedServiceFactoryTracker.provideConfiguration(ManagedServiceFactoryTracker.java:93) [8:org.apache.felix.configadmin:1.8.16]
	at org.apache.felix.cm.impl.ConfigurationManager$UpdateConfiguration.run(ConfigurationManager.java:1792) [8:org.apache.felix.configadmin:1.8.16]
	at org.apache.felix.cm.impl.UpdateThread.run0(UpdateThread.java:141) [8:org.apache.felix.configadmin:1.8.16]
	at org.apache.felix.cm.impl.UpdateThread.run(UpdateThread.java:109) [8:org.apache.felix.configadmin:1.8.16]
	at java.lang.Thread.run(Thread.java:748) [?:?]

That is weird, so investigating the bundle via headers:<bundle id> showed that the package edu.uci.ics.jung.graph is actually not imported. Okay, fine, that is easy to fix, simply adding a customized Import-Package statement to the related pom, to see if this will fix it.

<Import-Package>*,edu.uci.ics.jung.graph</Import-Package>

bundle:watch and mvn clean install and re-importing the graph, still resulted in a NoClassDefFoundError.

(╯°□°）╯︵ ┻━┻

Let’s try some debug magic. Hitting the breakpoint at GraphmlGraphContainerProvider.java:136 and trying to load the classes from the Evaluate Expression Dialog (IntelliJ)

Class.forName("edu.uci.ics.jung.graph.DirectedSparseGraph"); // NoClassDefFoundError. Okay that was expected.
Class.forName("edu.uci.ics.jung.graph.SparseGraph"); // Works. Hmm... wait, what?

So the last is working, but has the same package, so why is that working, but not the DirectedSparseGraph? Looking where the classes are coming from, it turns out they are from different maven modules, but share the same package. Usually I would simply change the packages, but unfortunately they are 3rd party dependencies, so this does not work. To solve this, we have to get shady and put the dependencies in one big jar using the maven-shade-plugin sigh

The pom for this looks like this (simplified)

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <groupId>org.opennms.features</groupId>
        <artifactId>org.opennms.features.graphs</artifactId>
        <version>24.0.0-SNAPSHOT</version>
    </parent>

    <!-- Feature Definition -->
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.opennms.features.graphs</groupId>
    <artifactId>org.opennms.features.graphs.jung</artifactId>
    <version>${jungVersion}</version>
    <description>shaded osgi bundle containing complete jung implementation</description>
    <packaging>bundle</packaging>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>2.4.3</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <artifactSet>
                            </artifactSet>
                            <createDependencyReducedPom>true</createDependencyReducedPom>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.felix</groupId>
                <artifactId>maven-bundle-plugin</artifactId>
                <extensions>true</extensions>
                <configuration>
                    <instructions>
                        <Export-Package>edu.uci.ics.jung.graph;version="${jungVersion}",edu.uci.ics.jung.graph.util;version="${jungVersion}"</Export-Package>
                    </instructions>
                    <unpackBundle>true</unpackBundle>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <dependencies>
        <dependency>
            <groupId>net.sf.jung</groupId>
            <artifactId>jung-api</artifactId>
            <version>${jungVersion}</version>
        </dependency>
        <dependency>
            <groupId>net.sf.jung</groupId>
            <artifactId>jung-graph-impl</artifactId>
            <version>${jungVersion}</version>
        </dependency>
    </dependencies>
</project>

Rebuilding and running the same commands from above, it finally "worked" \o/ So what did we learn?

One should not simply export the same packages in different modules when it comes to OSGI

┬─┬ ノ( ゜-゜ノ)

Side note

I was always wondering why the Topology Map is embedding the jung dependencies: click. This is probably why.

Disclaimer

By "it finally worked" I mean another Exception was thrown which is probably explained in the next post (-: