Improve RocketMQ integration example (#1757)

- The demo was unable to run and stop because of missing namesrv configuration, and now fixed.

sentinel-demo/sentinel-demo-rocketmq/src/main/java/com/alibaba/csp/sentinel/demo/rocketmq/Constants.java

@@ -19,6 +19,7 @@ public final class Constants {
 
     public static final String TEST_GROUP_NAME = "sentinel-group";
     public static final String TEST_TOPIC_NAME = "SentinelTopicTest";
+    public static final String TEST_NAMESRV_ADDR = "127.0.0.1:9876";
 
     private Constants() {}
 }

sentinel-demo/sentinel-demo-rocketmq/src/main/java/com/alibaba/csp/sentinel/demo/rocketmq/PullConsumerDemo.java

@@ -17,6 +17,7 @@ package com.alibaba.csp.sentinel.demo.rocketmq;
 
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ExecutorService;
@@ -55,10 +56,16 @@ public class PullConsumerDemo {
         initFlowControlRule();
 
         DefaultMQPullConsumer consumer = new DefaultMQPullConsumer(Constants.TEST_GROUP_NAME);
-
+        consumer.setNamesrvAddr(Constants.TEST_NAMESRV_ADDR);
         consumer.start();
 
-        Set<MessageQueue> mqs = consumer.fetchSubscribeMessageQueues(Constants.TEST_TOPIC_NAME);
+        Set<MessageQueue> mqs = new HashSet<>();
+        try {
+            mqs = consumer.fetchSubscribeMessageQueues(Constants.TEST_TOPIC_NAME);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+
         for (MessageQueue mq : mqs) {
             System.out.printf("Consuming messages from the queue: %s%n", mq);
             SINGLE_MQ:

sentinel-demo/sentinel-demo-rocketmq/src/main/java/com/alibaba/csp/sentinel/demo/rocketmq/SyncProducer.java

@@ -24,8 +24,8 @@ public class SyncProducer {
 
     public static void main(String[] args) throws Exception {
         // Instantiate with a producer group name.
-        DefaultMQProducer producer = new
-            DefaultMQProducer(Constants.TEST_GROUP_NAME);
+        DefaultMQProducer producer = new DefaultMQProducer(Constants.TEST_GROUP_NAME);
+        producer.setNamesrvAddr(Constants.TEST_NAMESRV_ADDR);
         // Launch the instance.
         producer.start();
         for (int i = 0; i < 1000; i++) {
@@ -33,9 +33,14 @@ public class SyncProducer {
             Message msg = new Message(Constants.TEST_TOPIC_NAME, "TagA",
                 ("Hello RocketMQ From Sentinel " + i).getBytes(RemotingHelper.DEFAULT_CHARSET)
             );
-            // Call send message to deliver message to one of brokers.
-            SendResult sendResult = producer.send(msg);
-            System.out.printf("%s%n", sendResult);
+
+            try {
+                // Call send message to deliver message to one of brokers.
+                SendResult sendResult = producer.send(msg);
+                System.out.printf("%s%n", sendResult);
+            } catch (Exception e) {
+                e.printStackTrace();
+            }
         }
         // Shut down once the producer instance is not longer in use.
         producer.shutdown();