add optional config parameter to specify an optional MQTT topic prefix

io.openems.edge.controller.api.mqtt/src/io/openems/edge/controller/api/mqtt/Config.java

@@ -23,6 +23,9 @@
 	@AttributeDefinition(name = "Edge-ID", description = "Client-ID for authentication at MQTT broker")
 	String clientId() default "edge0";
 
+	@AttributeDefinition(name = "Topic prefix", description = "Optional topic prefix (<topic_prefix>/edge/<edge_id>/...)")
+	String topicPrefix() default "";
+
 	@AttributeDefinition(name = "Username", description = "Username for authentication at MQTT broker")
 	String username();
 

io.openems.edge.controller.api.mqtt/src/io/openems/edge/controller/api/mqtt/ControllerApiMqtt.java

@@ -8,7 +8,6 @@
 
 public interface ControllerApiMqtt extends Controller, OpenemsComponent, EventHandler {
 
-	public static final String TOPIC_PREFIX = "edge/%s/";
 	public static final String TOPIC_CHANNEL_PREFIX = "channel/";
 	public static final String TOPIC_CHANNEL_LAST_UPDATE = "lastUpdate";
 	public static final String TOPIC_EDGE_CONFIG = "edgeConfig/";

io.openems.edge.controller.api.mqtt/src/io/openems/edge/controller/api/mqtt/ControllerApiMqttImpl.java

@@ -74,7 +74,7 @@ private void activate(ComponentContext context, Config config) throws Exception
 		this.config = config;
 
 		// Publish MQTT messages under the topic "edge/edge0/..."
-		this.topicPrefix = String.format(ControllerApiMqtt.TOPIC_PREFIX, config.clientId());
+		this.topicPrefix = createTopicPrefix(config);
 
 		super.activate(context, config.id(), config.alias(), config.enabled());
 		this.mqttConnector.connect(config.uri(), config.clientId(), config.username(), config.password(),
@@ -84,6 +84,31 @@ private void activate(ComponentContext context, Config config) throws Exception
 				});
 	}
 
+	/**
+	 * Creates the topic prefix in either format.
+	 * 
+	 * <ul>
+	 * <li>topic_prefix/edge/edge_id/
+	 * <li>edge/edge_id/
+	 * </ul>
+	 * 
+	 * @param config the {@link Config}
+	 * @return the prefix
+	 */
+	protected static String createTopicPrefix(Config config) {
+		final var b = new StringBuilder();
+		if (config.topicPrefix() != null && !config.topicPrefix().isBlank()) {
+			b //
+					.append(config.topicPrefix()) //
+					.append("/");
+		}
+		b //
+				.append("edge/") //
+				.append(config.clientId()) //
+				.append("/");
+		return b.toString();
+	}
+
 	@Override
 	@Deactivate
 	protected void deactivate() {

io.openems.edge.controller.api.mqtt/test/io/openems/edge/controller/api/mqtt/ControllerApiMqttImplTest.java

@@ -1,5 +1,8 @@
 package io.openems.edge.controller.api.mqtt;
 
+import static io.openems.edge.controller.api.mqtt.ControllerApiMqttImpl.createTopicPrefix;
+import static org.junit.Assert.assertEquals;
+
 import java.time.Instant;
 import java.time.ZoneOffset;
 
@@ -25,6 +28,7 @@ public void test() throws Exception {
 				.activate(MyConfig.create() //
 						.setId(CTRL_ID) //
 						.setClientId("edge0") //
+						.setTopicPrefix("") //
 						.setUsername("guest") //
 						.setPassword("guest") //
 						.setUri("ws://localhost:1883") //
@@ -36,4 +40,19 @@ public void test() throws Exception {
 						.build());
 	}
 
+	@Test
+	public void testCreateTopicPrefix() throws Exception {
+		assertEquals("foo/bar/edge/edge0/", createTopicPrefix(MyConfig.create() //
+				.setClientId("edge0") //
+				.setTopicPrefix("foo/bar") //
+				.build()));
+		assertEquals("edge/edge0/", createTopicPrefix(MyConfig.create() //
+				.setClientId("edge0") //
+				.setTopicPrefix("") //
+				.build()));
+		assertEquals("edge/edge0/", createTopicPrefix(MyConfig.create() //
+				.setClientId("edge0") //
+				.setTopicPrefix(null) //
+				.build()));
+	}
 }

io.openems.edge.controller.api.mqtt/test/io/openems/edge/controller/api/mqtt/MyConfig.java

@@ -12,6 +12,7 @@ protected static class Builder {
 		private PersistencePriority persistencePriority;
 		private boolean debugMode;
 		private String clientId;
+		private String topicPrefix;
 		private String username;
 		private String password;
 		private String certPem;
@@ -36,6 +37,11 @@ public Builder setClientId(String clientId) {
 			return this;
 		}
 
+		public Builder setTopicPrefix(String topicPrefix) {
+			this.topicPrefix = topicPrefix;
+			return this;
+		}
+
 		public Builder setUsername(String username) {
 			this.username = username;
 			return this;
@@ -112,6 +118,11 @@ public String clientId() {
 		return this.builder.clientId;
 	}
 
+	@Override
+	public String topicPrefix() {
+		return this.builder.topicPrefix;
+	}
+
 	@Override
 	public String username() {
 		return this.builder.username;