New FactoriesProvider interface

common/src/main/java/com/zegelin/cassandra/exporter/FactoriesProvider.java

@@ -0,0 +1,25 @@
+package com.zegelin.cassandra.exporter;
+
+import com.zegelin.cassandra.exporter.MBeanGroupMetricFamilyCollector.Factory;
+import com.zegelin.cassandra.exporter.cli.HarvesterOptions;
+
+import java.util.List;
+import java.util.ServiceLoader;
+
+/**
+ * Service Provider interface whose implementations will be loaded via {@link ServiceLoader}.
+ *
+ * <p> Allows runtime modules to provide pluggable metrics via classpath registration.
+ *
+ */
+public interface FactoriesProvider
+{
+    /**
+     * Provides a list of {@link Factory} to be registered on the exporter.
+     *
+     * @param metadataFactory
+     * @param options
+     * @return factories
+     */
+    List<Factory> getFactories(final MetadataFactory metadataFactory, final HarvesterOptions options);
+}

common/src/main/java/com/zegelin/cassandra/exporter/Harvester.java

@@ -141,6 +141,10 @@ public boolean equals(final Object o) {
 
     protected Harvester(final MetadataFactory metadataFactory, final HarvesterOptions options) {
         this.collectorFactories = new ArrayList<>(new FactoriesSupplier(metadataFactory, options).get());
+
+        ServiceLoader<FactoriesProvider> providers = ServiceLoader.load(FactoriesProvider.class);
+        providers.forEach(p -> collectorFactories.addAll(p.getFactories(metadataFactory, options)));
+
         this.metadataFactory = metadataFactory;
         this.exclusions = options.exclusions;
         this.enabledGlobalLabels = options.globalLabels;

common/src/main/java/com/zegelin/cassandra/exporter/MBeanGroupMetricFamilyCollector.java

@@ -37,7 +37,8 @@ public MBeanGroupMetricFamilyCollector removeMBean(final ObjectName mBeanName) {
     public abstract Stream<MetricFamily> collect();
 
 
-    protected interface Factory {
+    public interface Factory
+    {
         /**
          * Create a {@link MBeanGroupMetricFamilyCollector} for the given MBean, or null if this collector
          * doesn't support the given MBean.