Spring integration TCP server print incoming messages

Question

I am trying now for a while to get started with Spring Integration, but unfortunately can't get it to work.

I would like to have a server listening on a TCP port and printing out the data sent to it from the client. My client is another command line tool, but because I couldn't get it to work I am using this dummy client to send a message.

So far I looked into two examples and am lost which one to follow actually:

1. Blog post on TCP vending machine connection
2. The official annotation based example TcpClientServerAnnotationDemoTest.java which is the code here used.

@EnableIntegration
@IntegrationComponentScan
@Configuration
public class Config {

    @MessagingGateway(defaultRequestChannel = "toTcp")
    public interface Gateway {
        String viaTcp(String in);
    }


    @Bean
    public TcpInboundGateway tcpInGate(AbstractServerConnectionFactory connectionFactory) {
        TcpInboundGateway inGate = new TcpInboundGateway();
        inGate.setConnectionFactory(connectionFactory);
        inGate.setRequestChannel(fromTcp());
        return inGate;
    }

    @Bean
    public MessageChannel fromTcp() {
        return new DirectChannel();
    }

    @MessageEndpoint
    public static class Echo {

        @Transformer(inputChannel = "fromTcp", outputChannel = "toEcho")
        public String convert(byte[] bytes) {
            return new String(bytes);
        }

        @ServiceActivator(inputChannel = "toEcho")
        public String upCase(String in) {
            return in.toUpperCase();
        }

        @Transformer(inputChannel = "resultToString")
        public String convertResult(byte[] bytes) {
            return new String(bytes);
        }
    }

    @Bean
    public AbstractServerConnectionFactory serverCF() {
        return new TcpNetServerConnectionFactory(8000);
    }
}

and here my dummy client sending a message.

String host = "localhost";
int port = 8000;
InetAddress address = InetAddress.getByName(host);
socket = new Socket(address, port);

//Send the message to the server
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);

String myMessage = "THIS IS MY MESSAGE!";

String sendMessage = myMessage + "\n";
bw.write(sendMessage);
bw.flush();
System.out.println("Message sent to the server : "+ sendMessage);

//Get the return message from the server
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String message = br.readLine();
System.out.println("Message received from the server : " + message);

It does successfully create a TCP connection! But, where can I see the message? I was initially thinking that I could just print whatever passes through the @Transformer or @ServiceActivator but that didn't work.

2019-03-06 15:46:12.023 DEBUG 22941 --- [pool-2-thread-1] .s.i.i.t.c.TcpNetServerConnectionFactory : Accepted connection from 127.0.0.1:41178
2019-03-06 15:46:12.025 DEBUG 22941 --- [pool-2-thread-1] o.s.i.i.tcp.connection.TcpNetConnection  : New connection localhost:41178:8000:fdaf998f-7045-43e6-aa4a-2e4ecf6b1d9d
2019-03-06 15:46:12.025 DEBUG 22941 --- [pool-2-thread-1] .s.i.i.t.c.TcpNetServerConnectionFactory : serverCF: Added new connection: localhost:41178:8000:fdaf998f-7045-43e6-aa4a-2e4ecf6b1d9d
2019-03-06 15:46:12.025 TRACE 22941 --- [pool-2-thread-1] .s.i.i.t.c.TcpNetServerConnectionFactory : serverCF: Connection is open: localhost:41178:8000:fdaf998f-7045-43e6-aa4a-2e4ecf6b1d9d
2019-03-06 15:46:12.025 DEBUG 22941 --- [pool-2-thread-2] o.s.i.i.tcp.connection.TcpNetConnection  : localhost:41178:8000:fdaf998f-7045-43e6-aa4a-2e4ecf6b1d9d Reading...
2019-03-06 15:46:12.025 DEBUG 22941 --- [pool-2-thread-2] o.s.i.i.t.s.ByteArrayCrLfSerializer      : Available to read: 20
2019-03-06 15:46:12.026 TRACE 22941 --- [pool-2-thread-1] o.s.i.i.tcp.connection.TcpNetConnection  : Published: TcpConnectionOpenEvent [source=TcpNetConnection:localhost:41178:8000:fdaf998f-7045-43e6-aa4a-2e4ecf6b1d9d], [factory=serverCF, connectionId=localhost:41178:8000:fdaf998f-7045-43e6-aa4a-2e4ecf6b1d9d] **OPENED**

When I am using the actual client the command line tool, the connection is established as well, but any follow up messages send throw SocketTimeoutException.

I appreciate any help, as well as any suggestion for a tutorial on Spring Integration for TCP using annotations! Thank you!

Answer 1

To print the data from the client there is just enough to have a WireTap on the fromTcp or toEcho channel and tap it into some other channel for printing. Typically the LoggingHandler is enough to have as a subscriber to that wire-tapping channel.

You can see more info in the Reference Manual: https://docs.spring.io/spring-integration/docs/current/reference/html/#channel-interceptors