java-server websocket失败：WebSocket握手期间出错：意外的响应代码：404

Question

I am learning to create the web socket server in java with tomcat,

but when I run the tomcat9.0 with the sample code,

I always get the below error in the chrome developer tool response.

 **web socket failed: Error during WebSocket handshake: Unexpected response code: 404**

I query the much the reference, I still not resolve the problem,

I am use the tomcat9.0 & jre 1.8.0, and I refer the blog .

I create the server code(project -> new -> Servlet file) is

 package idv.yu;

 import java.io.IOException;
 import javax.websocket.OnClose;
 import javax.websocket.OnError;
 import javax.websocket.OnMessage;
 import javax.websocket.OnOpen;
 import javax.websocket.Session;
 import javax.websocket.server.ServerEndpoint;

 @ServerEndpoint(value = "/endpoint")
 public class MyWebsocket {

    @OnOpen
    public void onOpen(Session session) {
        System.out.println("onOpen::" + session.getId());
    }

    @OnClose
    public void onClose(Session session) {
        System.out.println("onClose::" + session.getId());
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        System.out.println("onMessage::From=" + session.getId() + "      Message=" + message);

        try {
            session.getBasicRemote().sendText("Hello Client " +      session.getId() + "!");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @OnError
    public void onError(Throwable t) {
        System.out.println("onError::" + t.getMessage());
    }
 }

My project tree structure is below:

In my chrome developer tool I set the code

 class WebSocketClient {

     constructor(protocol, hostname, port, endpoint) {

         this.webSocket = null;

    this.protocol = protocol;
    this.hostname = hostname;
    this.port     = port;
    this.endpoint = endpoint;
}

getServerUrl() {
    return this.protocol + "://" + this.hostname + ":" + this.port + this.endpoint;
}

connect() {
    try {
        this.webSocket = new WebSocket(this.getServerUrl());

        // 
        // Implement WebSocket event handlers!
        //
        this.webSocket.onopen = function(event) {
            console.log('onopen::' + JSON.stringify(event, null, 4));
        }

        this.webSocket.onmessage = function(event) {
            var msg = event.data;
            console.log('onmessage::' + JSON.stringify(msg, null, 4));
        }
        this.webSocket.onclose = function(event) {
            console.log('onclose::' + JSON.stringify(event, null, 4));                
             }
             this.webSocket.onerror = function(event) {
                 console.log('onerror::' + JSON.stringify(event, null, 4));
             }

         } catch (exception) {
             console.error(exception);
         }
     }

     getStatus() {
         return this.webSocket.readyState;
     }
     send(message) {

         if (this.webSocket.readyState == WebSocket.OPEN) {
             this.webSocket.send(message);

         } else {
             console.error('webSocket is not open. readyState=' + this.webSocket.readyState);
         }
     }
     disconnect() {
         if (this.webSocket.readyState == WebSocket.OPEN) {
             this.webSocket.close();

         } else {
             console.error('webSocket is not open. readyState=' + this.webSocket.readyState);
         }
     }
 }

the last I set the command below:

 var client = new WebSocketClient('ws', '127.0.0.1', 8080, '/WebsocketDemo/endpoint');
 client.connect();

But I get the error:

Have anyone known how to resolve the problem?

should the "web.xml" had to set any something?

my web.xml is default value, and I had check the project have websocket-api.jar file in the library.

Thank you very much.

-- edit--

my WebContent/Web-INF/web.xml content below:

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"      xmlns="http://xmlns.jcp.org/xml/ns/javaee"      xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID"      version="3.1">
   <display-name>WebsocketDemo</display-name>
   <welcome-file-list>
     <welcome-file>index.html</welcome-file>
     <welcome-file>index.htm</welcome-file>
     <welcome-file>index.jsp</welcome-file>
     <welcome-file>default.html</welcome-file>
     <welcome-file>default.htm</welcome-file>
     <welcome-file>default.jsp</welcome-file>
   </welcome-file-list>
 </web-app>

Answer 1

404 in websocket is not any different from 404 in HTTP, it means the address you are trying to reach can not be found on the server. In your case I think its about /WebsocketDemo part. The /endpoint is available in your endpoint configuration but its missing /WebsocketDemo . Perhaps you should deploy your WAR under /WebsocketDemo in webapps, or remove this part of the address.

Answer 2

I was resolved the problem,

Going to the eclipse → Project → build automatically checked the item,

My project is running correct evertime.

Using the websocket is not to put other jar file, the tomcat8,9 have websocket jar in lib folder.

thank @sepehr GH,@Al1