how to pass the parameters to Websocket endpoint hander - websocket

Question

When I create jetty websocket, I register my endpoint handler like this:
public class MyWebSocketEndpoint extends WebSocketServlet {
#Override
public void configure(WebSocketServletFactory webSocketServletFactory) {
webSocketServletFactory.register(MyEndpointHandler.class);
}
}
for MyEndpoingHandler class, I can't define a constructor with some parameters, or it will got runtime exception. How can I pass some parameters when create the MyEndpointHandler instance?

Answer 1

Use a WebSocketCreator.
When you call WebSocketServletFactory.register(MyEndpoingHandler.class) all that's happening internally is the equivalent of ...
#Override
public void register(Class<?> websocketPojo)
{
this.setCreator(new SingleEndpointCreator(websocketPojo));
}
Complete example on WebSocketCreator:
package websocket;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicInteger;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.handler.HandlerList;
import org.eclipse.jetty.servlet.DefaultServlet;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.websocket.api.Session;
import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
import org.eclipse.jetty.websocket.api.annotations.WebSocket;
import org.eclipse.jetty.websocket.servlet.ServletUpgradeRequest;
import org.eclipse.jetty.websocket.servlet.ServletUpgradeResponse;
import org.eclipse.jetty.websocket.servlet.WebSocketCreator;
import org.eclipse.jetty.websocket.servlet.WebSocketServlet;
import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
public class DemoWebSocketCreator
{
public static class MyWebSocketServlet extends WebSocketServlet
{
#Override
public void configure(WebSocketServletFactory wsFactory)
{
wsFactory.setCreator(new MyWebSocketCreator());
}
}
public static class MyWebSocketCreator implements WebSocketCreator
{
private AtomicInteger idGen = new AtomicInteger(0);
#Override
public Object createWebSocket(ServletUpgradeRequest servletUpgradeRequest, ServletUpgradeResponse servletUpgradeResponse)
{
String id = "ws" + idGen.incrementAndGet();
return new MyWebSocket(id);
}
}
#WebSocket
public static class MyWebSocket
{
private final String id;
public MyWebSocket(String id)
{
this.id = id;
}
#OnWebSocketMessage
public void onMessage(Session session, String msg)
{
try
{
session.getRemote().sendString("Hello, my id is [" + id + "]: You said: " + msg);
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
public static void main(String[] args) throws Exception
{
Server server = new Server(8080);
ServletContextHandler context = new ServletContextHandler();
context.setContextPath("/");
context.addServlet(MyWebSocketServlet.class, "/ws/");
// always last, and on default pathspec
context.addServlet(DefaultServlet.class, "");
HandlerList handlers = new HandlerList();
handlers.addHandler(context);
handlers.addHandler(new DefaultHandler());
server.setHandler(handlers);
server.start();
server.join();
}
}