java - Spring Boot TCP Client

Question

I'm looking for an example to connect TCP through sping boot without xml(spring-integration).

I got the following snippet from How to create a Tcp Connection in spring boot to accept connections? URL.

in this example, just main method alone enough to connect tcp. why other beans and the transformer are declared here?

Is it wrong? Instead of using simple Java socket client to accept the response, I would like to integrate with Spring. But no suitable examples available using Java DSL.

Could you please help?

package com.example;

import java.net.Socket;

import javax.net.SocketFactory;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.integration.annotation.ServiceActivator;
import org.springframework.integration.annotation.Transformer;
import org.springframework.integration.channel.DirectChannel;
import org.springframework.integration.ip.tcp.TcpReceivingChannelAdapter;
import org.springframework.integration.ip.tcp.connection.AbstractServerConnectionFactory;
import org.springframework.integration.ip.tcp.connection.TcpNetServerConnectionFactory;
import org.springframework.integration.transformer.ObjectToStringTransformer;
import org.springframework.messaging.MessageChannel;

@SpringBootApplication
public class So39290834Application {

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext context = SpringApplication.run(So39290834Application.class, args);
        Socket socket = SocketFactory.getDefault().createSocket("localhost", 9999);
        socket.getOutputStream().write("foo
".getBytes());
        socket.close();
        Thread.sleep(1000);
        context.close();
    }

    @Bean
    public TcpNetServerConnectionFactory cf() {
        return new TcpNetServerConnectionFactory(9999);
    }

    @Bean
    public TcpReceivingChannelAdapter inbound(AbstractServerConnectionFactory cf) {
        TcpReceivingChannelAdapter adapter = new TcpReceivingChannelAdapter();
        adapter.setConnectionFactory(cf);
        adapter.setOutputChannel(tcpIn());
        return adapter;
    }

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

    @Transformer(inputChannel = "tcpIn", outputChannel = "serviceChannel")
    @Bean
    public ObjectToStringTransformer transformer() {
        return new ObjectToStringTransformer();
    }

    @ServiceActivator(inputChannel = "serviceChannel")
    public void service(String in) {
        System.out.println(in);
    }

}

Answer 1

This application is both the client and the server.

That question was specifically about how to write the server side (accept the connection), using Spring Integration.

The main() method is simply a test that connects to the server side. It uses standard Java sockets APIs; it could also have been written to use Spring Integration components on the client side.

BTW, you don't have to use XML to write a Spring Integration application, you can configure it with annotations, or use the Java DSL. Read the documentation.

EDIT

Client/Server Example using Java DSL

@SpringBootApplication
public class So54057281Application {

    public static void main(String[] args) {
        SpringApplication.run(So54057281Application.class, args);
    }

    @Bean
    public IntegrationFlow server() {
        return IntegrationFlows.from(Tcp.inboundGateway(
                    Tcp.netServer(1234)
                        .serializer(codec()) // default is CRLF
                        .deserializer(codec()))) // default is CRLF
                .transform(Transformers.objectToString()) // byte[] -> String

                .<String, String>transform(p -> p.toUpperCase())
                .get();
    }

    @Bean
    public IntegrationFlow client() {
        return IntegrationFlows.from(MyGateway.class)
                .handle(Tcp.outboundGateway(
                    Tcp.netClient("localhost", 1234)
                        .serializer(codec()) // default is CRLF
                        .deserializer(codec()))) // default is CRLF
                .transform(Transformers.objectToString()) // byte[] -> String
                .get();
    }

    @Bean
    public AbstractByteArraySerializer codec() {
        return TcpCodecs.lf();
    }

    @Bean
    @DependsOn("client")
    ApplicationRunner runner(MyGateway gateway) {
        return args -> {
            System.out.println(gateway.exchange("foo"));
            System.out.println(gateway.exchange("bar"));
        };
    }

    public interface MyGateway {

        String exchange(String out);

    }

}

result

FOO
BAR