NatsClient refactor (#3914)

libraries/src/main/java/com/baeldung/jnats/NatsClient.java

@@ -1,31 +1,35 @@
 package com.baeldung.jnats;
 
-import io.nats.client.*;
-
-import java.io.IOException;
-import java.util.*;
-
+import io.nats.client.AsyncSubscription;
+import io.nats.client.Connection;
+import io.nats.client.Message;
+import io.nats.client.Nats;
+import io.nats.client.Options;
+import io.nats.client.Subscription;
+import io.nats.client.SyncSubscription;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-public class NatsClient {
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
 
-    private String serverURI;
+public final class NatsClient {
 
-    private Connection natsConnection;
+    private final String serverURI;
 
-    private Map<String, Subscription> subscriptions = new HashMap<>();
+    private final Connection natsConnection;
+
+    private final Map<String, Subscription> subscriptions = new HashMap<>();
 
     private final static Logger log = LoggerFactory.getLogger(NatsClient.class);
 
-    public NatsClient() {
+    NatsClient() {
         this.serverURI = "jnats://localhost:4222";
         natsConnection = initConnection(serverURI);
     }
 
-
     public NatsClient(String serverURI) {
-
         if ((serverURI != null) && (!serverURI.isEmpty())) {
             this.serverURI = serverURI;
         } else {
@@ -40,59 +44,33 @@ public class NatsClient {
         natsConnection.close();
     }
 
-
     private Connection initConnection(String uri) {
         try {
-
             Options options = new Options.Builder()
-              .errorCb(new ExceptionHandler() {
-                  @Override
-                  public void onException(NATSException ex) {
-                      log.error("Connection Exception: ", ex);
-                  }
-              })
-              .disconnectedCb(new DisconnectedCallback() {
-                  @Override
-                  public void onDisconnect(ConnectionEvent event) {
-                      log.error("Channel disconnected: {}", event.getConnection());
-                  }
-              })
-              .reconnectedCb(new ReconnectedCallback() {
-                  @Override
-                  public void onReconnect(ConnectionEvent event) {
-                      log.error("Reconnected to server: {}", event.getConnection());
-                  }
-              })
+              .errorCb(ex -> log.error("Connection Exception: ", ex))
+              .disconnectedCb(event -> log.error("Channel disconnected: {}", event.getConnection()))
+              .reconnectedCb(event -> log.error("Reconnected to server: {}", event.getConnection()))
               .build();
 
             return Nats.connect(uri, options);
-
         } catch (IOException ioe) {
             log.error("Error connecting to NATs! ", ioe);
             return null;
         }
     }
 
-
-    public void publishMessage(String topic, String replyTo, String message) {
+    void publishMessage(String topic, String replyTo, String message) {
         try {
-            // Simple Publisher
             natsConnection.publish(topic, replyTo, message.getBytes());
         } catch (IOException ioe) {
             log.error("Error publishing message: {} to {} ", message, topic, ioe);
         }
     }
 
-
     public void subscribeAsync(String topic) {
 
-        // Simple Async Subscriber
-        AsyncSubscription subscription = natsConnection.subscribe(topic, new MessageHandler() {
-            @Override
-            public void onMessage(Message msg) {
-                log.info("Received message on {}", msg.getSubject());
-            }
-        });
+        AsyncSubscription subscription = natsConnection.subscribe(
+          topic, msg -> log.info("Received message on {}", msg.getSubject()));
 
         if (subscription == null) {
             log.error("Error subscribing to {}", topic);
@@ -101,13 +79,11 @@ public class NatsClient {
         }
     }
 
-    public SyncSubscription subscribeSync(String topic) {
-        // Simple Sync Subscriber
+    SyncSubscription subscribeSync(String topic) {
         return natsConnection.subscribe(topic);
     }
 
     public void unsubscribe(String topic) {
-
         try {
             Subscription subscription = subscriptions.get(topic);
 
@@ -116,15 +92,12 @@ public class NatsClient {
             } else {
                 log.error("{} not found. Unable to unsubscribe.", topic);
             }
-
         } catch (IOException ioe) {
             log.error("Error unsubscribing from {} ", topic, ioe);
         }
     }
 
-
-    public Message makeRequest(String topic, String request) {
-
+    Message makeRequest(String topic, String request) {
         try {
             return natsConnection.request(topic, request.getBytes(), 100);
         } catch (IOException | InterruptedException ioe) {
@@ -133,7 +106,7 @@ public class NatsClient {
         }
     }
 
-    public void installReply(String topic, String reply) {
+    void installReply(String topic, String reply) {
         natsConnection.subscribe(topic, message -> {
             try {
                 natsConnection.publish(message.getReplyTo(), reply.getBytes());
@@ -143,8 +116,7 @@ public class NatsClient {
         });
     }
 
-    public SyncSubscription joinQueueGroup(String topic, String queue) {
+    SyncSubscription joinQueueGroup(String topic, String queue) {
         return natsConnection.subscribe(topic, queue);
     }
-
 }