replace reflection with a factory

Author: fbruton

src/main/java/emissary/grpc/channel/ChannelManager.java

@@ -112,13 +112,7 @@ public static ChannelManager ofSubClass(
 
     public static ChannelManager ofSubClass(
             Class<? extends ChannelManager> clz, String host, int port, Configurator configG, ChannelCredentials credentials) {
-        try {
-            return clz
-                    .getDeclaredConstructor(String.class, int.class, Configurator.class, ChannelCredentials.class)
-                    .newInstance(host, port, configG, credentials);
-        } catch (ReflectiveOperationException e) {
-            throw new IllegalStateException("Unable to instantiate new ChannelManager: " + e.getMessage(), e);
-        }
+        return ChannelManagerRegistry.ofSubClass(clz, host, port, configG, credentials);
     }
 
     /**

src/main/java/emissary/grpc/channel/ChannelManagerFactory.java

@@ -0,0 +1,10 @@
+package emissary.grpc.channel;
+
+import emissary.config.Configurator;
+
+import io.grpc.ChannelCredentials;
+
+@FunctionalInterface
+public interface ChannelManagerFactory {
+    ChannelManager create(String host, int port, Configurator configG, ChannelCredentials credentials);
+}

src/main/java/emissary/grpc/channel/ChannelManagerRegistry.java

@@ -0,0 +1,31 @@
+package emissary.grpc.channel;
+
+import emissary.config.Configurator;
+
+import io.grpc.ChannelCredentials;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class ChannelManagerRegistry {
+    private ChannelManagerRegistry() {
+        /* This utility class should not be instantiated */
+    }
+
+    private static final Map<Class<? extends ChannelManager>, ChannelManagerFactory> REGISTRY = new ConcurrentHashMap<>();
+
+    public static void register(Class<? extends ChannelManager> clz, ChannelManagerFactory factory) {
+        REGISTRY.put(clz, factory);
+    }
+
+    public static ChannelManager ofSubClass(
+            Class<? extends ChannelManager> clz, String host, int port, Configurator configG, ChannelCredentials credentials) {
+
+        ChannelManagerFactory factory = REGISTRY.get(clz);
+        if (factory == null) {
+            throw new IllegalArgumentException("No factory registered for class: " + clz.getName() +
+                    ". Make sure the class is loaded so its static initialization block runs.");
+        }
+        return factory.create(host, port, configG, credentials);
+    }
+}

src/main/java/emissary/grpc/channel/PooledChannelManager.java

@@ -47,6 +47,10 @@ public class PooledChannelManager extends ChannelManager implements PooledObject
     public static final String RETRIEVAL_ORDER = GRPC_CHANNEL_POOL_PREFIX + "RETRIEVAL_ORDER";
     public static final String TEST_BEFORE_BORROW = GRPC_CHANNEL_POOL_PREFIX + "TEST_BEFORE_BORROW";
 
+    static {
+        ChannelManagerRegistry.register(PooledChannelManager.class, PooledChannelManager::new);
+    }
+
     private final ObjectPool<ManagedChannel> channelPool;
 
     /**

src/main/java/emissary/grpc/channel/SingletonChannelManager.java

@@ -12,6 +12,10 @@
 public class SingletonChannelManager extends ChannelManager {
     private final ManagedChannel channel;
 
+    static {
+        ChannelManagerRegistry.register(SingletonChannelManager.class, SingletonChannelManager::new);
+    }
+
     /**
      * Constructs a new gRPC connection factory using the provided host, port, and configuration.
      *