NoSuchMethodError HttpServletRequest.getServletCon

I'm trying to set up a WebSocketServlet in Jetty.

I've set up a servlet according to this guide, and implemented the WebSocket according to this one. However, when I run gradle jettyRun and attempt to open a connection (using this) to ws://localhost:8080/myProjectName/echo), I get java.lang.NoSuchMethodError: javax.servlet.http.HttpServletRequest.getServletContext() (full stacktrace)

I see that this method was only introduced in servlet 3.0 - however, since I'm using servlet-api:3.1.0, I believe I should have that method?

I'm reasonably sure that the routing in my WEB-INF/web.xml is correct, since when I try to hit another url (ws://localhost:8080/myProjectName/echo123, for instance), I don't get error output on the terminal.

Files:

build.gradle:

apply plugin: 'java'
apply plugin : 'jetty'

sourceCompatibility = 1.5
version = '1.0'

repositories {
    mavenCentral()
}

dependencies {
    compile 'javax.servlet:javax.servlet-api:3.1.0'
    compile 'org.eclipse.jetty:jetty-server:9.3.2.v20150730'
    compile 'org.eclipse.jetty.websocket:websocket-servlet:9.0.0.M3'
    compile 'org.eclipse.jetty.aggregate:jetty-all:9.1.3.v20140225'
    testCompile group: 'junit', name: 'junit', version: '4.11'
}

src/main/webapp/WEB-INF/web.xml

<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         id="WebApp_ID" version="3.0">

    <servlet>
        <servlet-name>EchoServlet</servlet-name>
        <servlet-class>org.scubbo.myprojectname.EchoServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>EchoServlet</servlet-name>
        <url-pattern>/echo</url-pattern>
    </servlet-mapping>
</web-app>

src/main/java/org/scubbo/myprojectname/EchoServlet.java

package org.scubbo.myprojectname;

import org.eclipse.jetty.websocket.servlet.WebSocketServlet;
import org.eclipse.jetty.websocket.servlet.WebSocketServletFactory;
import org.scubbo.myprojectname.sockets.EchoSocket;

public class EchoServlet extends WebSocketServlet {

    @Override
    public void configure(WebSocketServletFactory factory) {
        factory.getPolicy().setIdleTimeout(10000);
        factory.register(EchoSocket.class);
    }

src/main/java/org/scubbo/myprojectname/sockets/EchoSocket.java

package org.scubbo.myprojectname.sockets;

import org.eclipse.jetty.websocket.api.Session;
import org.eclipse.jetty.websocket.api.annotations.OnWebSocketMessage;
import org.eclipse.jetty.websocket.api.annotations.WebSocket;

@WebSocket
public class EchoSocket {

    @OnWebSocketMessage
    public void onText(Session session, String message) {
        if (session.isOpen()) {
            System.out.printf("Echoing back message [%s]%n", message);
            session.getRemote().sendString(message, null);
        }
    }

}

The original problem you are having is that you had 2 conflicting versions of the servlet api in your classpath (not that uncommon, as there's a half-dozen odd maven coordinates for that artifact, which makes conflict resolution difficult for maven or gradle)

Don't use jetty-all with your project, that artifact isn't meant to be used from a project. See past responses about this.

The problem you are having with WebSocket support should be filed as a separate question on stackoverflow.

Ask a specific question about your websocket issue, and I'll answer there.