Singleton variables in Jersey web service

I have a RESTful web service based on JAX-RS and Jersey. I have a bunch of GET and POST Methods and inside of it i need "global" variables.

I have an initialization method with ServletContextListener and it's contextInitialized-Method for write some log files and do other stuff. In this method I want to declare variables wich I can access from anywhere in my application.

here are my code:

    @WebListener
    public class MyServletContextListener implements ServletContextListener {
//these are the variables I need in my other methods
        public String imagePath;
        public int entryCount;
        public int registeredUsers;
        public Connection connection;

        @Override
        public void contextInitialized(ServletContextEvent servletContextEvent) {
            System.out.println("initialization of service stared");
            System.out.println("reading config...");

            Configuration config = ConfigManager.readConfig("../service_config.xml");
            this.imagePath = config.getImagePath();

            System.out.println("try to get databse connection");
            connection = ConnectionHelper.getConnection(config.getDbName(),
                                                        config.getDbPassword(),
                                                        config.getDbUser());

            System.out.println("database connection successful established");
            // here are some db actions...
        }

        @Override
        public void contextDestroyed(ServletContextEvent servletContextEvent) {
            System.out.println("shutdown service");
        }
    }

For example: At init, I read an config file, count some stats from database and read an image path-string for a directory out of my config file.

When a GET method is called, I want to read the String variable of the image path and increase a counter by 1.

@Path("/entries")
public class EntryService {
@GET
    @Path("/images/{imageId}")
    @Produces({"image/png"})
    public Response getEntryImage(@PathParam("imageId") long imageId) {
        String filePath = <* HERE I NEED THE IMAGE PATH FROM INIT *>;
        File file = new File(filePath + imageId + ".png");

        if (file.exists()) {
            Response.ResponseBuilder response = Response.ok((Object) file);
            response.header("Content-Disposition", "attachment; filename=image_from_server.png");

            return response.build();
        } else {
            Response.ResponseBuilder response = Response.status(204);
            return response.build();
        }
    }
}

How do I realize that? (I read something about EJB and Singleton-Annotation but didn't get it work).

If a library or component needs some extra dependencies in my pom.xml file, please tell me how to implement it.