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I wrote a basic java server class. When it handles the "shutdown" request, it calls server.stop(0) and the spins in place. Why is this happening?

I copied most of the code from this StackOverflow post. The only significant modification to this code is that I added the server.stop(0).

Other facts: I am running this using java 8 and I am running this through IntelliJ.

package good.question.ask.questions.stackoverflow;

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;

import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;

public class ServerTester2
{
    private HttpServer server = null;
    public static void main(String[] args) throws Exception {
    ServerTester2 serverTester2 = new ServerTester2();
    serverTester2.start();
}
void start()
{
    try {
        server = HttpServer.create(new InetSocketAddress(8000), 0);
    } catch (IOException e) {
        e.printStackTrace();
    }
    server.createContext("/shutdown", new MyHandler());
    server.setExecutor(null); // creates a default executor
    server.start();
}

class MyHandler implements HttpHandler
{
    @Override
    public void handle(HttpExchange t) throws IOException
    {
        String response = "This is the response";
        t.sendResponseHeaders(200, response.length());
        OutputStream os = t.getResponseBody();
        os.write(response.getBytes());
        os.close();
        t.close();
        System.out.println("Stopping Server...");
        stop();
        System.out.println("Server Stopped!");
    }
}

void stop()
{
    server.stop(0);
}
}

Currently, the server returns a response message to the client (I tested that using postman), and then prints "Stopping Server" to the console. After that, the server object seems to be shut down, because when I send it more requests it doesn't respond to them, however, the thread running the server continues to spin.

Minimally, I expected the server to reach this line of code 

System.out.println("Server Stopped!");

but it never does.

More to the point, I expected the server thread to terminate but instead, it just spins.

Why is this happening? (Do I have a deadlock in the code somewhere?) Is there a better way to handle server shutdown (using the httpserver library)?

RealUser
  • 75
  • 8
  • Have you tried doing `t.close()` in your `handle(...)` method? – Joakim Danielson Sep 13 '19 at 12:34
  • yes I have tried that as well (in my first test code) – RealUser Sep 13 '19 at 12:37
  • My guess is then that you can't call stop from that method because the server is waiting for the `handle()` method to finish and the 'handle' method waits for the server to stop... – Joakim Danielson Sep 13 '19 at 12:43
  • @JoakimDanielson, If that's true, then what is the proper way to hand shutdown? Meaning, when the client calls "http://localhost:8000/shutdown" how can my server properly handle that request to ensure it shuts down properly? (If it can't do it in the handler, then where/how can it be done?) – RealUser Sep 13 '19 at 12:49
  • @RealUser: you can always start a new thread that calls `servers.stop()`. The only drawback is that the `shutdown` command won't be able to report success/error in that case. – Joachim Sauer Sep 13 '19 at 12:50
  • I feel like what I am asking to do should be pretty standard (and I just don't know how to look it up). Shouldn't there be some obvious/classic way to enable a client to shut down the server? – RealUser Sep 13 '19 at 12:53
  • @RealUser: no, most servers can't be shut down by the client, mostly because a server tends to serve many clients. Also, the class you use isn't exactly a standard class (it's available in Oracle JDKs and OpenJDK, but not part of the Java standard). – Joachim Sauer Sep 13 '19 at 12:55

0 Answers0