Spring Boot - How to get the running port

Question

I have a spring boot application (using embedded tomcat 7), and I've set server.port = 0 in my application.properties so I can have a random port. After the server is booted up and running on a port, I need to be able to get the port that that was chosen.

I cannot use @Value("$server.port") because it's zero. This is a seemingly simple piece of information, so why can't I access it from my java code? How can I access it?

Answer 1

Is it also possible to access the management port in a similar way, e.g.:

  @SpringBootTest(classes = {Application.class}, webEnvironment = WebEnvironment.RANDOM_PORT)
  public class MyTest {

    @LocalServerPort
    int randomServerPort;

    @LocalManagementPort
    int randomManagementPort;

Answer 2

Spring's Environment holds this information for you.

@Autowired
Environment environment;

String port = environment.getProperty("local.server.port");

On the surface this looks identical to injecting a field annotated @Value("${local.server.port}") (or @LocalServerPort, which is identical), whereby an autowiring failure is thrown at startup as the value isn't available until the context is fully initialised. The difference here is that this call is implicitly being made in runtime business logic rather than invoked at application startup, and hence the 'lazy-fetch' of the port resolves ok.

Answer 3

Thanks to @Dirk Lachowski for pointing me in the right direction. The solution isn't as elegant as I would have liked, but I got it working. Reading the spring docs, I can listen on the EmbeddedServletContainerInitializedEvent and get the port once the server is up and running. Here's what it looks like -

import org.springframework.boot.context.embedded.EmbeddedServletContainerInitializedEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;




    @Component
    public class MyListener implements ApplicationListener<EmbeddedServletContainerInitializedEvent> {

      @Override
      public void onApplicationEvent(final EmbeddedServletContainerInitializedEvent event) {
          int thePort = event.getEmbeddedServletContainer().getPort();
      }
    }

Answer 4

You can get the port that is being used by an embedded Tomcat instance during tests by injecting the local.server.port value as such:

// Inject which port we were assigned
@Value("${local.server.port}")
int port;

Answer 5

Starting with Spring Boot 1.4.0 you can use this in your test:

import org.springframework.boot.context.embedded.LocalServerPort;

@SpringBootTest(classes = {Application.class}, webEnvironment = WebEnvironment.RANDOM_PORT)
public class MyTest {

  @LocalServerPort
  int randomPort;

  // ...
}

Answer 6

Just so others who have configured their apps like mine benefit from what I went through...

None of the above solutions worked for me because I have a ./config directory just under my project base with 2 files:

application.properties
application-dev.properties

In application.properties I have:

spring.profiles.active = dev  # set my default profile to 'dev'

In application-dev.properties I have:

server_host = localhost
server_port = 8080

This is so when I run my fat jar from the CLI the *.properties files will be read from the ./config dir and all is good.

Well, it turns out that these properties files completely override the webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT setting in @SpringBootTest in my Spock specs. No matter what I tried, even with webEnvironment set to RANDOM_PORT Spring would always startup the embedded Tomcat container on port 8080 (or whatever value I'd set in my ./config/*.properties files).

The ONLY way I was able to overcome this was by adding an explicit properties = "server_port=0" to the @SpringBootTest annotation in my Spock integration specs:

@SpringBootTest (webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT, properties = "server_port=0")

Then, and only then did Spring finally start to spin up Tomcat on a random port. IMHO this is a Spring testing framework bug, but I'm sure they'll have their own opinion on this.

Hope this helped someone.

Answer 7

None of these solutions worked for me. I needed to know the server port while constructing a Swagger configuration bean. Using ServerProperties worked for me:

import javax.annotation.PostConstruct;
import javax.inject.Inject;
import javax.ws.rs.ApplicationPath;

import io.swagger.jaxrs.config.BeanConfig;
import io.swagger.jaxrs.listing.ApiListingResource;
import io.swagger.jaxrs.listing.SwaggerSerializers;

import org.glassfish.jersey.server.ResourceConfig;
import org.springframework.stereotype.Component;

@Component
@ApplicationPath("api")
public class JerseyConfig extends ResourceConfig 
{
    @Inject
    private org.springframework.boot.autoconfigure.web.ServerProperties serverProperties;

    public JerseyConfig() 
    {
        property(org.glassfish.jersey.server.ServerProperties.BV_SEND_ERROR_IN_RESPONSE, true);
    }

    @PostConstruct
    protected void postConstruct()
    {
        // register application endpoints
        registerAndConfigureSwaggerUi();
    }

    private void registerAndConfigureSwaggerUi()
    {
        register(ApiListingResource.class);
        register(SwaggerSerializers.class);

        final BeanConfig config = new BeanConfig();
        // set other properties
        config.setHost("localhost:" + serverProperties.getPort()); // gets server.port from application.properties file         
    }
}

This example uses Spring Boot auto configuration and JAX-RS (not Spring MVC).