How to receive and reply on Spring - spring

Question

I'm trying to deploy a RPC (request/reply pattern) and I'm using RabbitMQ and Spring in the server side because I need dynamic consumers. I can configurate dynamic consumers with SimpleMessageListenerContainer but i don't know how to reply my message.
Here is my class configuration:
#Configuration
public class dynamicConsumerConfig {
private static Properties prop = new Properties();
public static void setPropValues() throws IOException {
File configFile = new File("src/main/resources/config.properties");
InputStream inStream = new FileInputStream(configFile.getAbsolutePath());
prop.load(inStream);
}
#Bean
public Queue slowQueue() {
return new Queue("slowQueue");
}
#Bean
public Queue fastQueue() {
return new Queue("fastQueue");
}
#Bean
public DirectExchange exchange1() {
return new DirectExchange("pdfqueues");
}
#Bean
public Binding slowBind(DirectExchange exchange, Queue slowQueue) {
return BindingBuilder.bind(slowQueue)
.to(exchange)
.with("slow");
}
#Bean
public Binding fastBind(DirectExchange exchange, Queue fastQueue) {
return BindingBuilder.bind(fastQueue)
.to(exchange)
.with("fast");
}
#Bean
public ConnectionFactory connect() throws IOException {
setPropValues();
CachingConnectionFactory connection = new CachingConnectionFactory();
connection.setHost(prop.getProperty("HOST"));
connection.setUsername(prop.getProperty("USER"));
connection.setPassword(prop.getProperty("PASS"));
connection.setPort(Integer.parseInt(prop.getProperty("PORT")));
return connection;
}
#Bean
public SimpleMessageListenerContainer container1(ConnectionFactory connection) throws IOException {
SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
setPropValues();
container.setConnectionFactory(connection);
container.setQueueNames("slowQueue");
container.setMessageListener(firstListener());
container.setMaxConcurrentConsumers(8);
container.setConcurrentConsumers(1);
container.setConsecutiveActiveTrigger(1);
container.setConsecutiveIdleTrigger(1);
container.setTxSize(1);
container.setPrefetchCount(1);
return container;
}
#Bean
public MessageListener firstListener()
{
return new MessageListener() {
#Override
public void onMessage(Message message) {
PdfBoxService pdfboxservice = new PdfBoxService(prop.getProperty("tmpPath"),prop.getProperty("imagicPath"),prop.getProperty("resources"),
prop.getProperty("tessdata"),prop.getProperty("languages"));
String picture = new String(message.getBody(), StandardCharsets.UTF_8);
List<ImagePair> lip = null;
try {
lip = new ArrayList<ImagePair>();
lip.add(new ImagePair("JPG", picture));
} catch (FileNotFoundException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
ByteArrayOutputStream output= pdfboxservice.ImgToPdf(lip, false, false, false, 1, 1);
} catch (IOException | InterruptedException | TransformerException | BadFieldValueException
| TesseractException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
};
}
In the fuction firstListener() i get the message. In this case is a picture. The picture is converted from JPG to PDF. The PDF is stored in outputvariable.
I need to reply this output in other queue but i don't have tools for do it.
I think that my code is a bad pattern but I don't know how to do a RPC pattern with dynamic consumers using SimpleMessageListenerContainer.

Answer 1

Use a MessageListenerAdapter with a POJO method that returns a result instead of implementing MessageListener yourself.
Starting with version 2.0, a convenient FunctionalInterface has been provided:
#FunctionalInterface
public interface ReplyingMessageListener<T, R> {
R handleMessage(T t);
}
This facilitates convenient configuration of the adapter using Java 8 lamdas:
new MessageListenerAdapter((ReplyingMessageListener<String, String>) data -> {
...
return result;
}));