HOAB

Problem :

A very specific and particular problem.

I want to deploy  a SpringBoot application, in an OSGI environment, in a external Jetty server…

So I found solution do deploy Springboot in OSGI : here or here. Very good by the wat.

And also to deploy Springboot as war for an external Tomcat…

Too easy, my external Jetty server was rejecting Servlet 3.0 application startup… (hard coding for : 

context.setAttribute("org.eclipse.jetty.containerInitializers", initializers);

Yes, it's better, starting a 1,25 days of try and success !

Solution :

My first web application was deployed with Spring Dispatcher Servlet with a BundleActivator

My second web application was deployed with Spring DispatcherServlet AND a SpringBootApplication intialized with the ressource loader of the BundleActivator (as in the OSGI example) : component-scan is working ! 

My third web application was switching to an initialization Servlet 3.0 with an extension of ServletContainerInitializer, thanks to harded jetty configuration, it's not working

My third and a half remove all web.xml content to keep only a context listener as my Jetty was doing nothing : 

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0">

    <!-- ServletContainerInitializer can not be used here -->
    <!-- XXXXXXX is putting in hard : context.setAttribute("org.eclipse.jetty.containerInitializers with only Jasper -->

    <!-- At the end, it's possible to load SpringBoot with this context listener -->
    <listener>
        <listener-class>
            com.hexagon.introscope.extension.MyContextLoaderListener
        </listener-class>
    </listener>

</web-app>

My fourth web application was trying to load the Springboot application file as a YAML file (why so simple !), resolved with a “hack” :

• The ServletContext has a way to store the configuration directory, during the initialization, I saved it somewhere : HpaContextLoaderListener.getConfigDirectory() 

The listener loader : 

package com.xxxxx.extension;

import org.eclipse.jetty.webapp.WebAppContext;
import org.springframework.web.context.WebApplicationContext;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletException;
import java.io.File;
import java.nio.file.Path;

public class MyContextLoaderListener implements ServletContextListener {

    private static File configDirectory;

    public static File getConfigDirectory() {
        return configDirectory;
    }

    public void contextInitialized(ServletContextEvent event) {
        ServletContext servletContext = event.getServletContext();
        MySpringBootHexagonActivator app = new MySpringBootHexagonActivator();

        try {
            configDirectory = servletContext.getAttribute("introscope.em"));
            
            InstantiateHelper.getValueByMethod(servletContext, "setExtendedListenerTypes", new Class[]{boolean.class}, true);

            app.onStartup(event.getServletContext());
        } catch (ServletException e) {
            throw new RuntimeException(e);
        }
    }

    public void contextDestroyed(ServletContextEvent event) {
    }
}

@SpringBootApplication
public class MySpringBootHexagonActivator extends SpringBootServletInitializer {

    protected SpringApplicationBuilder createSpringApplicationBuilder() {
        SpringApplicationBuilder builder = super.createSpringApplicationBuilder();
        Map<String, Object> properties = new HashMap<>();
        Path propertyFile = Path.of(MyContextLoaderListener.getConfigDirectory().getPath(), "application-extension.yml");
        properties.put("spring.config.location", propertyFile.toString());
        builder.properties(properties);
        builder.resourceLoader(HpaHexagonActivator.getResourceResolver());

        return builder;
    }
}

The HpaHexagonActivator.getResourceResolver() is the trick from SpringBoot OSGI example to load classes from Bundle classpath. I store the ressources resolver in a static variable that I can access from everywhere.

A word on that one : 

InstantiateHelper.getValueByMethod(servletContext, "setExtendedListenerTypes", new Class[]{boolean.class}, true);

I'm in OSGI, Jetty controls the listener class, and Springboot is unknown. You can authorized additional listeners but in my case, Jetty is not exported by the other OSGI package, not able to call it simply so… reflection : InstantiateHelper is basically a helper class to call methods by reflection.

At the end : 

1. Springboot starts
2. Springboot scans package offered by BundleActivator ressource locator
3. Springboot can use an external configuration file, in YAML
4. Springboot starts REST & Database
5. It was hard.

Of course, lot of tries between these big steps !

The goal is to extend a 3rd party product without having source code.