Project: Apache RocketMQ (App Definition and Development / Streaming & Messaging)
File: Example_Simple.md

Two functions below are provided in the basic sample: The RocketMQ can be utilized to send messages in three ways: reliable synchronous, reliable asynchronous, and one-way transmission. The first two message types are reliable because there is a response whether they were sent successfully. The RocketMQ can be utilized to consume messages. maven: ``` java <dependency> <groupId>org.apache.rocketmq</groupId> <artifactId>rocketmq-client</artifactId> <version>4.3.0</version> </dependency> ``` gradle: ``` java compile 'org.apache.rocketmq:rocketmq-client:4.3.0' ``` Reliable synchronous transmission is used in extensive scenes, such as important notification messages, SMS notification. ``` java public class SyncProducer { public static void main(String[] args) throws Exception { // Instantiate with a producer group name DefaultMQProducer producer = new DefaultMQProducer("pleaserenameuniquegroupname"); // Specify name server addresses producer.setNamesrvAddr("localhost:9876"); // Launch the producer instance producer.start(); for (int i = 0; i < 100; i++) { // Create a message instance with specifying topic, tag and message body Message msg = new Message("TopicTest" / Topic /, "TagA" / Tag /, ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET) / Message body / ); // Send message to one of brokers SendResult sendResult = producer.send(msg); // Check whether the message has been delivered by the callback of sendResult System.out.printf("%s%n", sendResult); } // Shut down once the producer instance is not longer in use producer.shutdown(); } } ``` Asynchronous transmission is generally used in response time sensitive business scenarios. It means that it is unable for the sender to wait the response of the Broker too long. ``` java public class AsyncProducer { public static void main(String[] args) throws Exception { // Instantiate with a producer group name DefaultMQProducer producer = new DefaultMQProducer("pleaserenameuniquegroupname"); // Specify name server addresses producer.setNamesrvAddr("localhost:9876"); // Launch the producer instance producer.start(); producer.setRetryTimesWhenSendAsyncFailed(0); for (int i = 0; i < 100; i++) { final int index = i; // Create a message instance with specifying topic, tag and message body Message msg = new Message("TopicTest", "TagA", "OrderID188", "Hello world".getBytes(RemotingHelper.DEFAULT_CHARSET)); // SendCallback: receive the callback of the asynchronous return result. producer.send(msg, new SendCallback() { @Override public void onSuccess(SendResult sendResult) { System.out.printf("%-10d OK %s %n", index, sendResult.getMsgId()); } @Override public void onException(Throwable e) { System.out.printf("%-10d Exception %s %n", index, e); e.printStackTrace(); } }); } // Shut down once the producer instance is not longer in use producer.shutdown(); } } ``` One-way transmission is used for cases requiring moderate reliability, such as log collection. ``` java public class OnewayProducer { public static void main(String[] args) throws Exception{ // Instantiate with a producer group name DefaultMQProducer producer = new DefaultMQProducer("pleaserenameuniquegroupname"); // Specify name server addresses producer.setNamesrvAddr("localhost:9876"); // Launch the producer instance producer.start(); for (int i = 0; i < 100; i++) { // Create a message instance with specifying topic, tag and message body Message msg = new Message("TopicTest" / Topic /, "TagA" / Tag /, ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET) / Message body / ); // Send in one-way mode, no return result producer.sendOneway(msg); } // Shut down once the producer instance is not longer in use producer.shutdown(); } } ``` ``` java public class Consumer { public static void main(String[] args) throws InterruptedException, MQClientException { // Instantiate with specified consumer group name DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("pleaserenameuniquegroupname"); // Specify name server addresses consumer.setNamesrvAddr("localhost:9876"); // Subscribe one or more topics and tags for finding those messages need to be consumed consumer.subscribe("TopicTest", "*"); // Register callback to execute on arrival of messages fetched from brokers consumer.registerMessageListener(new MessageListenerConcurrently() { @Override public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) { System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs); // Mark the message that have been consumed successfully return ConsumeConcurrentlyStatus.CONSUME_SUCCESS; } }); // Launch the consumer instance consumer.start(); System.out.printf("Consumer Started.%n"); } } ```