pom.xml

<!-- 웹소켓 -->
<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-websocket</artifactId>
  <version>${org.springframework-version}</version>
</dependency>

servlet-context.xml

1. beans에 xmlns:websocket="http://www.springframework.org/schema/websocket" 추가
2. schemalocation에 http://www.springframework.org/schema/websocket http://www.springframework.org/schema/websocket/spring-websocket-4.3.xsd 추가
   
3. handler 추가, class 속성값은 클래스 파일 경로를 입력해야 한다.
   path 속성값인 /websocket로 소켓 메세지가 전송되면, webSocketHandler 클래스로 보내준다는 의미이다.

<!-- WebSocket -->
<beans:bean id="webSocketHandler" class="com.common.websocket.WebSocketHandler" />
<websocket:handlers>
  <websocket:mapping handler="webSocketHandler" path="/websocket"/>
  <websocket:handshake-interceptors>
    <beans:bean class="org.springframework.web.socket.server.support.HttpSessionHandshakeInterceptor"/>
  </websocket:handshake-interceptors>
</websocket:handlers>

web.xml

servlet 태그 내부에 <async-supported>true</async-supported>를 추가해준다. 다수의 클라이언트들이 동시에 정보를 보내기 위한 설정이다.

<!-- Processes application requests -->
<servlet>
  <servlet-name>appServlet</servlet-name>
  <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
  <init-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath*:/config/context/servlet-context.xml</param-value>
  </init-param>
  <load-on-startup>1</load-on-startup>
  <async-supported>true</async-supported>
</servlet>

WebSocketHandler.java

package com.common.websocket;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import javax.annotation.Resource;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.socket.CloseStatus;
import org.springframework.web.socket.TextMessage;
import org.springframework.web.socket.WebSocketSession;

import com.april.app.biz.frnt.FrontDAO;
import com.common.session.login.std.StandardAuthSuccessHandler;

public class WebSocketHandler {
		private static final Logger log = LoggerFactory.getLogger(StandardAuthSuccessHandler.class);
		
		@Resource(name = "FrontDAO")
		private FrontDAO FrontDAO;
		
		@Autowired
		public void setAlarmDAO(FrontDAO FrontDAO) {
			this.FrontDAO = FrontDAO;
		}

		//전체 세션
		private static List<WebSocketSession> sessions = new ArrayList<WebSocketSession>();
		//개인
		//		private Map<String, WebSocketSession> userSessionsMap = new HashMap<String, WebSocketSession>();
		

		//클라이언트가 서버에 접속 성공시 호출
		public void afterConnectionEstablished(WebSocketSession session) throws Exception {
			sessions.add(session); //리스트에 접속한 session들을 담음
		}
		
		//소켓에 메세지를 보냈을 때 호출
		protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
			for(WebSocketSession single : sessions) {
				// String memId = message.getPayload();
				Map<String, Object> count = FrontDAO.selectStatusCountInfo();
				int newCount = Integer.parseInt(count.toString());
				
				//newCount가 0이 아닐 경우 메세지 전송
				if(newCount != 0) {
					TextMessage sendMsg = new TextMessage(newCount + "개");
					single.sendMessage(sendMsg);
				}
			}
		}

		//연결이 종료됐을 때
		public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
			//전체 세션리스트에서 세션 삭제 
			sessions.remove(session);
		}
}

JSP

window.onload = function(){
    let webSocket = new WebSocket("ws://localhost");
    
    webSocket.onopen = () => {
        webSocket.send();
        wsSend();
    }
    
    webSocket.onmessage = (e) => {
//      console.log("핸들러에서 전송한 메세지",e.data);
        var status = document.querySelector(".status");
        console.log(status, '-> status');
        staus.innerText = e.data;
    }

    var wsSend=()=>{
        setInterval(function() {
            // 3초마다 클라이언트로 메시지 전송
            webSocket.send();
        }, 3000);
    }
}

결과는 실패 bean 주입이 안된다... 어찌할꼬

https://bmangrok.tistory.com/entry/WebSocket-%EC%8A%A4%ED%94%84%EB%A7%81-%EC%B1%84%ED%8C%85-%EA%B5%AC%ED%98%84-1
https://admm.tistory.com/81
https://simplehanlab.github.io/add-websocket
https://velog.io/@rim/%EC%9B%B9%EC%86%8C%EC%BC%93%EC%9C%BC%EB%A1%9C-%EC%8B%A4%EC%8B%9C%EA%B0%84-%EC%95%8C%EB%A6%BC-%EB%A7%8C%EB%93%A4%EA%B8%B01
https://hoon2kc.tistory.com/entry/websocket-%EC%8B%A4%EC%8B%9C%EA%B0%84-%EC%95%8C%EB%A6%BC