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How to rollback in saga pattern when a service fails

I am starting with Saga pattern using Spring cloud and rabbit mq. Following is the problem statement:
I call /service1 (producer) which publishes a message in rabbit mq and that message is consumed by the consumer service.
Now occurs tow cases:
Case 1: Consumer service does its part successfully.
Case 2: Consumer service fails to do its part, thus /service1 has to rollback its changes.
How does /service1 know if consumer is successful or not, so that it can send a success/failure response. Following is the project structure:
Producer:
#RestController
public class ProducerController {
private MessageChannel greet;
public ProducerController(HelloBinding binding) {
greet = binding.greeting();
}
#GetMapping("/greet/{name}")
public void publish(#PathVariable String name) {
String greeting = "Hello, "+name+"!";
Message<String> msg = MessageBuilder.withPayload(greeting)
.build();
this.greet.send(msg);
System.out.println("Message sent to the queue");
AMQP.Basic.Ack;
}
Consumer:
#EnableBinding(HelloBinding.class)
public class HelloListener {
#StreamListener(target=HelloBinding.GREETING)
public void processHelloChannelGreeting(String msg) {
System.out.println("Message received:- "+msg);
}
}
Now how do I tell the producer whether consumer's action is a success or a failure so that producer service sends appropriate response?

The producer can not know what happens after a message has been successfully published to a topic. If you want feedback from the consumer then you need to create a new "response" topic on which the consumer communicates success or failure of processing that message.
You can map the messages by keys.

Notifying the Websocket when no message received in PUBSUB

Below is my Message Listener which listens to Redis PUBSUB. It is working fine. I have to implement a feature in such a way that if no messages are received after threshold/specified time, then I have to send a proper message to websocket(subscription URL same as PUBSUB channel). I don't see any way to that as there will be many clients which subscribes to different channels at different times.
Any help or suggestion would be appreciable.
public class PubSubListener implements MessageListener {
#Autowired
private SimpMessagingTemplate simpMessagingTemplate ;
#Override
public void onMessage(Message message, byte[] pattern) {
logger.info(" MESSAGE RECEIVED FROM PUBSUB ");
simpMessagingTemplate.convertAndSend(new String(pattern), message.toString());
}
}

How to create an asynchronous singleton socket server with spring-integration?

I want to achieve the following using spring-integration: having a singleton open socket that constantly receives and writes data, asyncrhon!
This means I have to open a socket that constantly reads from the single socket, dispatches each message for async processing, and return the responses over the socket also async.
How can I achieve that asynchron pattern?
Especially: how can I use Serializer/Deserializer? As far as I understood, a serializer is only invoked on a new socket connection, so in my case only once at start of the first message?
#Configuration
public class SocketConfig {
#Bean
public TcpConnectionFactoryFactoryBean tcpFactory(MyConverter converter) {
TcpConnectionFactoryFactoryBean fact = new TcpConnectionFactoryFactoryBean();
fact.setType("server");
fact.setPort(PORT);
fact.setUsingNio(true); //should I use true or false?
fact.setSingleUse(false); //keep socket constantly open
fact.setSerializer(converter);
fact.setDeserializer(converter);
return fact;
}
#Bean
public TcpInboundGateway serverGateway(
#Qualifier("tcpFactory") TcpConnectionFactoryFactoryBean factory,
#Qualifier("serverChannel") MessageChannel serverChannel) throws Exception {
TcpInboundGateway g = new TcpInboundGateway();
g.setConnectionFactory(factory.getObject());
g.setRequestChannel(serverChannel);
return g;
}
}
#MessageEndpoint
public class SocketEndpoint {
#ServiceActivator(inputChannel = "serverChannel")
public Object run(Object obj) {
}
}
#Service
public class MyConverter implements Serializer<Object>, Deserializer<Object> {
//read from socket
#Override
public Object deserialize(InputStream inputStream) {
}
//send back to socket
#Override
public void serialize(Object message, OutputStream outputStream) {
}
}

A gateway is used for individual request/response pairs.
If you need to send multiple responses for a single request, you must use collaborating channel adapters as described in the documentation.
Collaborating adapters can also be used (server-side or client-side) for totally asynchronous communication (rather than with request/reply semantics).
On the server side, care must be taken to populate the ip_connectionId header because it is used to correlate the message to a connection. Messages that originate at the inbound adapter will automatically have the header set. If you wish to construct other messages to send, you will need to set the header. The header value can be captured from an incoming message.

Use #SentTo to send a message with Spring Boot and RabbitMq

Is it possible to send a return value of any method to a queue using an annotation, like
#SentTo("my.queue.name")
String send() {
return myString;
}
Do I definitely need a #RabbitListener to use #SendTo? Maybe another way out?
I'm trying to simplify my code.

#SendTo is only currently for replies from a #RabbitListener where the sender didn't set a replyTo header.
You could do what you want with a Spring Integration #Publisher annotation with its channel wired to a rabbitmq outbound channel adapter...
#Publisher(channel = "amqpOutboundChannel")
public String send() {
return myString;
}
#Bean
#ServiceActivator(inputChannel = "amqpOutboundChannel")
public AmqpOutboundEndpoint amqpOutbound(AmqpTemplate amqpTemplate) {
AmqpOutboundEndpoint outbound = new AmqpOutboundEndpoint(amqpTemplate);
outbound.setRoutingKey("my.queue.name"); // default exchange - route to queue 'my.queue.name'
return outbound;
}
The method has to be public and invoked from outside the bean itself.

how to capture subscribe event in my webSocket server with Spring 4

I did a simple web socket communication with spring 4, STOMP and sock.js, following this https://spring.io/guides/gs/messaging-stomp-websocket/
Now I want to upgrade it to simple chat. My problem is that when user subscribes to new chat room, he should get past messages. I don't know how to capture the moment when he subscribed to send him the list of the messages.
I tried using #MessageMapping annotation, but didn't reach any success:
#Controller
public class WebSocketController {
#Autowired
private SimpMessagingTemplate messagingTemplate;
#MessageMapping("/chat/{chatId}")
public void chat(ChatMessage message, #DestinationVariable String chatId) {
messagingTemplate.convertAndSend("/chat/" + chatId, new ChatMessage("message: " + message.getText()));
}
#SubscribeMapping("/chat")
public void chatInit() {
System.out.println("worked");
int chatId = 1; //for example
messagingTemplate.convertAndSend("/chat/" + chatId, new ChatMessage("connected"));
}
}
Then I created that:
#Controller
public class ApplicationEventObserverController implements ApplicationListener<ApplicationEvent> {
#Override
public void onApplicationEvent(ApplicationEvent applicationEvent) {
System.out.println(applicationEvent);
}
}
It works, but captures all possible events, I don't think it is a good practice.
So, my question can be rephrased: how to send initial data when user subscried to sth?

You can return anything directly to a client when it subscribes to a destination using a #SubscribeMapping handler method. The returned object won't go to the broker but will be sent directly to the client:
#SubscribeMapping("/chat")
public Collection<ChatMessage> chatInit() {
...
return messages;
}
On the client side:
socket.subscribe("/app/chat", function(message) {
...
});
Check out the chat example on GitHub, which shows this exact scenario.