[FIXED] Java Testcontainers - Cannot connect to exposed port

Issue

I implemented a POP3 server and client using javax.mail just to try doing integration testing with Docker. So I created two Docker images based on the openjdk:8-jre image and copied my jars to them and started it. Based on my configuration (see below) it is working. They are talking to each other.

But as want to have multiple integration tests it is going to be tedious to build an image for each one and starting them. Also I don't know how to automate the results. But then I stumbled across TestContainers and it seems that this would be big help when implementing those tests.

So I started to port those tests to TestContainers using my POP3 Server image as a GenericContainer and starting my POP3 Client classes in the JUnit test method. I exposed the port 24999 which my POP3 Server is listening to. But when I try to connect to the server I get the following error:

com.sun.mail.util.MailConnectException: Couldn't connect to host, port: localhost, 32782; timeout -1;
  nested exception is:
    java.net.ConnectException: Connection refused
...

There is probably some setting I am missing in TestContainers. Could you please help me.

Here is the code I am using:

public class DockerPop3AutocryptKeyProvidingAndReceivingTest {
    @Test
    public void test() throws InterruptedException {
        GenericContainer container = new GenericContainer<>("immerfroehlich/emailfilter:latest")
                .withExposedPorts(24999);
        
        container.start();
        
        String host = container.getContainerIpAddress();
        String port = container.getFirstMappedPort().toString();

        //The following is simplified, but copied from the working jar used in the Docker Client image/container
        MyPOP3Client client = new MyPOP3Client(host, port);
        client.connect();
        
        container.stop();
    }
}

This is how I create my Docker image:

FROM openjdk:8-jre

ADD build/distributions/MyPOP3Server.tar . #This is where I have packed all the needed files to. It gets unpacked by Docker.
#EXPOSE 24999 #I tried both with and without this expose
WORKDIR /MyPOP3Server/bin
ENTRYPOINT ["sh","MyPOP3Server"] #Executes the shell script which runs java with my jar

This is a simplified version of the code that is running inside the Server Jar:

MyPOP3Server server = new MyPOP3Server();
server.listenToPort(24999);

Please tell me what am I missing. What is wrong here?

Thanks and kind regards.

Solution

Thanks for all of your help. This led me towards the solution. It has been a combination of the missing WaitStrategy and problems with the port mapping.

Here is what I did: 1) In the MyPop3Server.listenToPort(String port) method I added a System.out.println:

public class MyPop3Server {
  public void listenToPort(String port) {
     //simplified: do initialization and listenToPort
     System.out.println("Awaiting Connection...");
  }
}

In my test I added a LogMessageWaitStrategy that listens for "Awaiting Connection"

GenericContainer container = new GenericContainer<>("immerfroehlich/emailfilter:latest")
   .waitingFor(Wait.forLogMessage("Awaiting Connection.*", 1))
   .withExposedPorts(24999);

2) I switched from container.getFirstMappedPort() to

container.getMappedPort(24999);

Here is the whole changed and working test code:

public class DockerPop3AutocryptKeyProvidingAndReceivingTest {
    @Test
    public void test() throws InterruptedException {
        GenericContainer container = new GenericContainer<>("immerfroehlich/emailfilter:latest")
                .waitingFor(Wait.forLogMessage("Awaiting Connection.*", 1))
                .withExposedPorts(24999);

        container.start();

        String host = container.getContainerIpAddress();
        String port = container.getMappedPort(24999).toString();

        //The following is simplified, but copied from the working jar used in the Docker Client image/container
        MyPOP3Client client = new MyPOP3Client(host, port);
        client.connect();

        container.stop();
    }
}

Thank you everyone.

Answered By - NoradX
Answer Checked By - Terry (JavaFixing Volunteer)