Error during WebSocket handshake: Unexpected response code: 404

Madhav Ayyagari Fri, 23 Oct 2015 09:36:15 -0700

Hi all,
I’m trying make Websockets work with embedded Tomcat (8.0.28) started by Main 
class (shown below). When I try to open websocket connection from browser using 
the URLs below, I always get “Error during WebSocket handshake: Unexpected 
response code: 404”.
Is there anything wrong with the way Tomcat is started/setup or classpath used 
in running the application?


Any help is greatly appreciated.
-Madhav

WS URLs getting the error:

http://localhost:8080/entities
http://localhost:8080/ws2/entities

Http URLs that show html page (but are not successful in connecting to 
websocket):
http://localhost:8080/ws2/hello

Main class that starts Tomcat:

package com.mypackage;

public class TomcatWebServer {

  public static void main(String[] args) {
    Tomcat tomcat = new Tomcat();
    tomcat.setPort(8080);

    Context ctx = tomcat.addContext("/ws2", new File(".").getAbsolutePath());

    Set<Class<?>> classes = new HashSet<>();
    classes.add(MyWebSocketEndpoint.class);
    ctx.addServletContainerInitializer(new WsSci(), classes);

    Tomcat.addServlet(ctx, "hello", new HttpServlet() {
      protected void service(HttpServletRequest req, HttpServletResponse resp)
          throws ServletException, IOException {
        Writer w = resp.getWriter();
        w.write("<html><head><script>"
                + "var wsUri=\"ws://localhost:8080/ws2/entities\";"
                + "var ws=new WebSocket(wsUri);"
                + "ws.onopen=function(evt){console.log(\"opened: 
\"+JSON.stringify(evt));};"
                + "ws.onclose=function(evt){console.log(\"closed: 
\"+JSON.stringify(evt));};"
                + "</script></head><body><h1>Hello, World!</h1></body></html>");
        w.flush();
      }
    });
    ctx.addServletMapping("/hello", "hello");

    try {
      tomcat.start();
      tomcat.getServer().await();
    } catch (LifecycleException e) {
      e.printStackTrace();
    }
  }

}


WebSocket implementing Class:

@ServerEndpoint("/entities")
public class MyWebSocketEndpoint {

  private Map<String, Session> clientSessions = new HashMap<>();

  @OnOpen
  public void onOpen(Session session) {
    System.out.println("session opened = " + session.getId());
    clientSessions.put(session.getId(), session);
  }

  @OnMessage
  public void onMessage(String message) {
    System.out.println("message = " + message);
  }

  @OnClose
  public void onClose(Session session) {
    System.out.println("session close = " + session.getId());
    clientSessions.remove(session.getId());
  }

  void broadcast(String message) {
    for (Session session : clientSessions.values()) {
      session.getAsyncRemote().sendText(message);
    }
  }
}


Gradle build file:

apply plugin: 'java'
apply plugin: 'idea'

repositories {
   mavenCentral()
}

configurations {
    provided
}

sourceSets {
    main {
        compileClasspath += configurations.provided
    }

}

idea {
    module {
        scopes.PROVIDED.plus += [configurations.provided]
    }
}

task run() {
    dependsOn build
    doLast {
        javaexec {
            main = 'com.mypackage.TomcatWebServer'
            classpath = sourceSets.main.output + 
sourceSets.main.runtimeClasspath
            println 'classpath for running ' + main + ' is ' + 
classpath.getAsPath()
        }
    }
}

dependencies {
    compile 'log4j:log4j:1.2.17'
    compile 'org.apache.tomcat.embed:tomcat-embed-core:8.0.28'
    compile 'org.apache.tomcat.embed:tomcat-embed-logging-log4j:8.0.28'
    compile 'org.apache.tomcat.embed:tomcat-embed-websocket:8.0.28'
    compile 'org.apache.tomcat:tomcat-websocket-api:8.0.28'
//    provided 'javax.websocket:javax.websocket-api:1.1'
}


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Error during WebSocket handshake: Unexpected response code: 404

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