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In my Spring Boot application I need to wait until the (default Tomcat) web server is fully initialized and ready to take traffic before I send messages to other applications telling them to send HTTP requests to me (specifically a monitoring system that hits my /health).

I've tried putting the logic that sends messages to other applications in a ApplicationListener<ContextRefreshedEvent> but it's still too early. The other applications try to make requests to me and fail. Right now I've put a delay in the onApplicationEvent and that works but it's hacky and racy.

I've also tried adding a ServletContextInitializer but that fired even earlier.

I'm assuming that I'll need to use a Tomcat API but I wanted to see if there was something in the Boot API for this.

sourcedelica
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  • Have you seen: http://stackoverflow.com/a/4747639/283084? Additionally maybe you can hide your app behind an LB and the LB won't take your app into it's pool until a request to `/health` returns HTTP OK (200). – harpun Feb 01 '15 at 19:19

2 Answers2

19

The simplest thing to do is to send the message once SpringApplication.run() has returned. This method won't return until Tomcat (or any other supported embedded container) is fully started and listening on the configured port(s). However, while this is simple, it's not a very neat approach as it mixes the concerns of your main configuration class and some of your application's runtime logic.

Instead, you can use a SpringApplicationRunListener. finished() will not be called until Tomcat is fully started and listening on the configured port.

Create a file named src/main/resources/META-INF/spring.factories listing your run listener. For example:

org.springframework.boot.SpringApplicationRunListener=com.example.MyRunListener

Create your run listener with the required constructor and implement SpringApplicationRunListener. For example:

package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.SpringApplicationRunListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.core.env.ConfigurableEnvironment;

public class MyRunListener implements SpringApplicationRunListener {

    public MyRunListener(SpringApplication application, String[] args) { }

    @Override
    public void starting() { }

    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) { }

    @Override
    public void contextPrepared(ConfigurableApplicationContext context) { }

    @Override
    public void contextLoaded(ConfigurableApplicationContext context) { }

    @Override
    public void started(ConfigurableApplicationContext context) {
        // Send message; Tomcat is running and listening on the configured port(s)
    }

    @Override
    public void running(ConfigurableApplicationContext context) { }

    @Override
    public void failed(ConfigurableApplicationContext context, Throwable exception) { }
Andy Wilkinson
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    Works great. I created another interface that the interested beans can implement and my `SpringApplicationRunListener` pulls them out of the context and calls them, so the logic can stay in the relevant bean(s). – sourcedelica Feb 02 '15 at 20:45
  • This doesn't work for me at all. The finished() method is called almost immediately and certainly well before the application is up and running. – onnoweb Mar 13 '18 at 01:17
  • @onnoweb I can't see how that would happen as the finished method is called at the end of `SpringApplication.run` processing. Perhaps you can ask a question of your own with a [minimal, complete, and verifiable example](/help/mcve) that shows finished being called earlier than expected. – Andy Wilkinson Mar 13 '18 at 12:19
  • I narrowed down my issue: ApplicationReadyEvent gets fired just before Tomcat is up and running. Using a CommandLineRunner instead of listening for ApplicationReadyEvent fixed my issue. – onnoweb Mar 13 '18 at 16:45
  • This interface has been updated; newer implementations should now use the `running` method. – Ian Mc Feb 18 '19 at 21:07
  • Good point, @IanMc. I've edited my answer to align with Spring Boot 2.x. – Andy Wilkinson Feb 19 '19 at 09:35
8

Since Spring Boot 1.3.0 this can also be accomplished by implementing ApplicationListener<ApplicationReadyEvent>

example:

public class MyApplicationListener implements ApplicationListener<ApplicationReadyEvent>, Ordered {

    @Override
    public void onApplicationEvent(ApplicationReadyEvent event) {
        //do stuff now that application is ready
    }

    @Override
    public int getOrder() {
        return Ordered.LOWEST_PRECEDENCE;
    }
}

Also, as mentioned in the accepted answer, you can create a file named src/main/resources/META-INF/spring.factories listing your ApplicationListener. For example:

org.springframework.context.ApplicationListener=com.example.MyApplicationListener

however, in my case, I only needed this listener to run under a specific profile

so I added the following property to application-<profile_name>.properties

context.listener.classes=com.example.MyApplicationListener
mjj1409
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