[FIXED] Jetty: Pass object from main method to servlet

Issue

I have two classes Server (with the main method, starting the server) and StartPageServlet with a Servlet.

The most important part of the code is:

public class Server {
    public static void main(String[] args) throws Exception {
        // some code

        // I want to pass "anObject" to every Servlet.
        Object anObject = new Object();

        Server server = new Server(4000);
        ServletContextHandler context = 
            new ServletContextHandler(ServletContextHandler.SESSIONS);
        context.addServlet(StartPageServlet.class, "/");
        // more code
}

And the StartPageServlet:

public class StartPageServlet extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
            throws ServletException, IOException
    {
        // Here I want to access "anObject"
    }

How do I do this?

Solution

Embedded Jetty is so wonderful here.

You have a few common options:

1. Direct instantiation of the servlet, use constructors or setters, then hand it off to Jetty via the ServletHolder (can be any value or object type)
2. Add it to the ServletContext in your main, and then access it via the ServletContext in your application (can be any value or object type).

Examples:

package jetty;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;

public class ObjectPassingExample
{
    public static void main(String args[]) throws Exception
    {
        Server server = new Server(8080);

        ServletContextHandler context = new ServletContextHandler();
        context.setContextPath("/");

        // Option 1: Direct servlet instantiation and ServletHolder
        HelloServlet hello = new HelloServlet("everyone");
        ServletHolder helloHolder = new ServletHolder(hello);
        context.addServlet(helloHolder, "/hello/*");

        // Option 2: Using ServletContext attribute
        context.setAttribute("my.greeting", "you");
        context.addServlet(GreetingServlet.class, "/greetings/*");

        server.setHandler(context);
        server.start();
        server.join();
    }

    public static class HelloServlet extends HttpServlet
    {
        private final String hello;

        public HelloServlet(String greeting)
        {
            this.hello = greeting;
        }

        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
        {
            resp.setContentType("text/plain");
            resp.getWriter().println("Hello " + this.hello);
        }
    }

    public static class GreetingServlet extends HttpServlet
    {
        private String greeting;

        @Override
        public void init() throws ServletException
        {
            this.greeting = (String) getServletContext().getAttribute("my.greeting");
        }

        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
        {
            resp.setContentType("text/plain");
            resp.getWriter().println("Greetings to " + this.greeting);
        }
    }
}

Answered By - Joakim Erdfelt
Answer Checked By - Marilyn (JavaFixing Volunteer)